Radiology and the role of imaging
Computed tomography of the thorax
Abdominal X-ray: useful landmarks
Effective use of the radiology department relies on good communication between radiologists and their clinical colleagues. The overall aim must be to target investigations efficiently in order to provide answers to clinical dilemmas at minimal cost and radiation dose (see Table 13.1). The investigation of neurological problems has been transformed by the advent of CT and MRI. Local availability varies and CT, in particular, can add considerably to the radiation burden. Conversely, if a CT is likely to provide the best answer and minimize overall costs by resulting in an early discharge, then it should be the investigation of choice. It is helpful to consider plain films, contrast studies, US, and then CT/MRI as a hierarchy where plain films are requested as an initial investigation. This hierarchy may be circumvented if a more expensive investigation is likely to produce the definitive result.
The following are important points to consider:
•Will the investigation alter patient management? That is, is the expected outcome clinically relevant? Do you need it?
•Investigating too often or repeating investigations before there has been an adequate lapse of time to allow resolution or to allow treatment to take effect. Similarly, investigations performed too early may be non-contributory. Do I need it now? Especially relevant when investigations may have been performed elsewhere. Make every effort possible to obtain prior studies. Transfer of digital data through electronic links will assist in this process. Has it been done already?
•Would an investigation that does not use ionizing radiation be more appropriate, e.g. USS/MRI?
•Failure to provide accurate clinical information and questions that you are hoping will be answered by the investigation may result in an unsatisfactory outcome or an inappropriate focus in the report. Have I explained the problem?
•Would another technique be more appropriate? The advances in radiology mean that discussion with a radiologist may be helpful in determining the best possible test. Is this the best investigation?
•Over-investigating. Are you taking comfort in too many tests or providing reassurance to the patient in this way?
Table 13.1 Typical effective doses from diagnostic medical exposures
| Procedure | Typical effective dose (mSv) | Equivalent number of CXRs | Equivalent period background radiation |
| Chest (P-A) | 0.015 | 1 | 2.5 days |
| Lumbar spine | 0.6 | 40 | 3 months |
| Abdomen | 0.4 | 30 | 2 months |
| IVU | 2.1 | 140 | 11.5 months |
| Mammography (two views) | 0.5 | 35 | 3 months |
| Barium enema | 2.2 | 150 | 1 year |
| CT head | 1.4 | 90 | 7.5 months |
| CT chest | 6.6 | 440 | 3 years |
| CT abdomen | 5.6 | 370 | 2.5 years |
| CT colonography | 10 | 670 | 4.5 years |
| Bone scan (99mTc) | 3 | 200 | 1.4 years |
| PET scan (body) (F18-FDG) | 18 | 1200 | 8.1 years |
UK average background radiation = 2.2mSv/year.1
Table adapted from Royal College of Radiologists (2012) Guidelines for Doctors. Making the best use of clinical radiology services. Doses for conventional X-ray examinations are based on data compiled by the Health Protection agency (HPA) from a survey of UK hospitals in 2008. The doses for CT examinations and radionuclide studies are compiled from surveys conducted by the HPA and the British Nuclear Medicine Society.
Wilhelm Roentgen discovered X-rays in 1895. X-rays form part of the electromagnetic spectrum, with microwaves and radio waves lying at the low-energy end, visible light in the middle, and X-rays at the high-energy end. They are energetic enough to ionize atoms and break molecular bonds as they penetrate tissues and are therefore called ionizing radiation. Diagnostic X-rays are produced when high-energy electrons strike a high atomic number material. This interaction is produced within an X-ray tube. A high voltage is passed across two tungsten terminals. One terminal (cathode) is heated until it liberates free electrons. When a high voltage is applied across the terminals, the electrons accelerate towards the anode at high speed. On hitting the anode target, X-rays are produced.
The X-ray picture is a result of the interaction of the ionizing radiation with tissues as it passes through the body. Tissues of different densities are displayed as distinct areas, depending on the amount of radiation absorbed. There are four basic densities in conventional radiography: gas (air), fat, soft tissue and fluid, and calcified structures. Air absorbs the least amount of X-rays and therefore appears black on the radiograph, whereas calcified structures and bone absorb the most, resulting in a white density. Soft tissues and fluid have a similar absorptive capacity and therefore appear grey on a radiograph.
X-ray film is exposed by light photons emitted by intensifying screens sensitive to radiation transmitted through the patient. Storage phosphor technology uses photostimulatable phosphor screens to convert X-ray energy directly into digital signals. The ↑ dynamic range and image contrast of digital radiography, compared with conventional film screen combinations, and the facility to manipulate signal intensity after image capture reduce the number of repeat exposures. This ↑ efficiency and minimizes patient radiation dose. Digital images can be made available on a local network for reporting by a radiologist or for review on a ward-based computer. Picture archiving and communication systems (PACS) are efficient at image production and manipulation and in the storage, retrieval, and transmission of data. PACS facilitates remote radiology reporting and alleviates workflow pressures. The vast majority of imaging studies conducted in the UK are stored, manipulated, and shared via a picture archiving and communication system. PACS has been rolled out to all healthcare organizations over the last decade or more as local, regional, or national implementations with different degrees of connectivity to radiology information systems (RIS), either via a local RIS or shared with other organizations (domain-based). Global challenges to PACS systems include management of ↑ volumes of imaging data and the ability to data-share across a spectrum of healthcare communities. Advantages include inventive ways of providing diagnostic imaging coverage, for instance in remote or scantily populated communities.
In order to interpret a plain P-A or lateral CXR, some knowledge of chest anatomy and the major landmarks on the film is required. We have highlighted the major bony and soft tissue structures visible on the plain film in order to make it easier to spot abnormalities. Patient positioning for a P-A CXR (see Figs 13.1–13.3) and lateral CXR (see Figs 13.4–13.6) is illustrated below.
The chest film is the most widely requested, yet most easy to misinterpret, investigation. Using a logical approach will avoid most pitfalls. This should be the initial imaging modality in all patients with suspected thoracic pathology.
•Always obtain prior imaging, if available; temporal changes assist greatly in image interpretation and differential diagnosis.
•Standard projections of the chest are P-A (posteroanterior) vs AP (anteroposterior). See 
Projection below.
•Additional views to aid problem-solving include lordotic, oblique, and decubitus projections (see below).
•Initially assess the technical quality.
P-A vs AP will determine whether assessment of the cardiac size is reliable.
Potential other views include:
•Lateral: improves visualization of the retrocardiac space and thoracic spine; earlier and more sensitive detection of effusions.
•Lateral decubitus: assesses for pleural effusion or pneumothorax in immobile patients (portable US also has a utility in this setting).
•Lordotic: angled beam allows better view of the apices which are typically obscured by the clavicles and anterior ribs.
Erect films enable a more accurate assessment of the mediastinum, since the lungs are more expanded, and allow detection of air–fluid levels, pleural thickening, and comment on the size of the pulmonary vasculature.
Look for the relationship of the medial ends of the clavicles to the spinous process at the same level; a common cause of unilateral transradiancy is rotation.
Ideally, six ribs should be seen anteriorly and ten ribs posteriorly. If more, this suggests hyperinflation (does the patient have asthma or COPD?). If less (e.g. poor inspiratory effort, obesity, or restrictive chest disorders), there will be apparent cardiomegaly, ↑ basal shadowing, and less commonly tracheal deviation.
Quality of image can be assessed by the degree of penetration. The thoracic disc spaces should be just visible through the heart. Absence of respiratory or motion artefact.
Sequentially consider the heart, mediastinum, lungs, diaphragms, soft tissues (breast shadows), and bones. Remember to assess your review areas—the lung apices, behind the heart, under the diaphragm, and the costophrenic angles.
This should lie between the fifth and seventh ribs. If flattened, consider hyperinflation. In 90% of cases, the right is higher than the left by 3–4cm. Effacement of the interface between the lung and diaphragm suggests pleural or pulmonary pathology. Loss of smooth contour suggests localized herniation (eventration). Peaks laterally may be due to subpulmonary effusion.
The upper trachea is central with a slight displacement to the right inferiorly due to the oesophagus. Thickening of the paratracheal line (>5mm) may imply nodal enlargement.
Look at the following parameters:
2.Date and time of study should be included in the report.
4.If there are lines, catheters, drains, endotracheal tube (ETT), etc., comment on the position. If new lines, comment on changes in position or if any removed.
5.Cardiac and mediastinal size and shape.
7.Lung disease. Pattern of disease as well as its evolution over time.
8.Interval changes from one film to the next as well as over time.
The mediastinum should be central. The heart is normally <50% of the thoracic width. Mediastinal enlargement or widening is a non-specific finding. The silhouette sign may help, but a lateral film is helpful for localization. Table 13.2 gives a list of distinguishing features that enable distinction of mediastinal masses from intra-pulmonary masses.
Normal variants mimicking a wide mediastinum are:
•Mediastinal fat (steroids, obesity).
•Vascular tortuosity—elderly patients.
•Low inspiratory supine position.
Table 13.2 Differentiating mediastinal from pulmonary masses
| Mediastinal mass | Pulmonary mass |
| Epicentre lies in mediastinum | Epicentre in lung |
| Obtuse angles with lung | Acute angles |
| No air bronchograms | Air bronchograms possible |
| Smooth and sharp margins | Irregular margins |
| Moves on swallowing | Moves with respiration |
| Bilateral | Unilateral |
The mediastinum is divided into three arbitrary compartments to aid in the differential diagnosis of a mediastinal mass (see Table 13.3). As there are no anatomical planes separating these divisions, disease can spread from one compartment to the next.
Table 13.3 Radiographic localization of a mediastinal mass
| Location of mass | Signs associated with mass in this compartment |
| Anterior mediastinum | |
| Middle mediastinum | |
| Posterior mediastinum | Distortion or displacement of the following: |
Based on the location of the mediastinal abnormality, possible pathologies include:
•Superior mediastinum: thymoma, retrosternal thyroid, and lymphoma.
•Anterior mediastinum (anterior line formed by the anterior trachea and the posterior border of the heart and great vessels): lymphoma (Hodgkin’s disease (HD) and non-Hodgkin’s lymphoma (NHL)), germ cell tumours, thymoma, retrosternal goitres, and Morgagni hernias (low).
•Middle mediastinum (extends behind the anterior mediastinum to a line 1cm posterior to the anterior border of the thoracic vertebral bodies): aortic aneurysm, bronchial carcinoma, foregut duplication cysts (including bronchogenic/oesophageal), and hiatus hernia.
•Posterior mediastinum (posterior to line described above): neurogenic tumours, Bochdalek hernia, dilated oesophagus, or aorta.
Mediastinal air may be due to a number of sources.
•Intraperitoneum and retro-peritoneum.
Signs include: subcutaneous emphysema, pneumopericardium, elevated thymus (sail sign), or air around major structures such as the PmA, bronchial wall.
May be seen in any compartment.
•Pleural and extra-pleural masses generally form obtuse angles with the adjacent pleura.
•Pulmonary or intra-parenchymal masses form acute angles with the pleura.
•The lateral view is more sensitive, as accumulation of fluid occurs first in the posterior recess.
•May cause mediastinal/tracheal shift to the contralateral side or adjacent atelectasis.
•US invaluable (and better than plain film) in evaluation of small effusions and guiding thoracocentesis.
•If blunting of the costophrenic angles is present, it indicates the presence of fluid of at least 200mL (P-A) or 75mL (lateral view) or may be 2° to thickening of the pleura.
•Pleural thickening most commonly a sequela of inflammatory change.
•Asbestos exposure results in a spectrum of pleural abnormality, ranging from benign plaques to fibrosis and malignant mesothelioma (obtain occupational history).
•Pleural effusion can be divided into either a transudate or an exudate.
•Transudate: ultrafiltrate of plasma, low in protein, no inflammatory cells.
•Exudate: rich in protein, cells, and debris.
•On an erect film, the partially collapsed lung is delineated from pleural air as a curvilinear line (visceral pleura) paralleling the chest wall.
•On a supine film, the changes are more subtle; look for the deep (costophrenic) sulcus sign, the double diaphragm sign (the dome and anterior portions of the diaphragm outlined by the lung and pleural air, respectively), hyperlucent thorax, and sharpening of mediastinal structures.
•Subtle pneumothorax will be more readily apparent on an expiratory film or a lateral decubitus film (accumulation of air superiorly).
•If the air is under tension, there may be mediastinal shift (tension pneumothorax). This can result in vascular compromise. On imaging:
•The lung appears over-expanded.
•Mediastinal shift and of the heart to contralateral side.
•Indication: exclude malignancy; obtain a sample for culture.
•USS used to determine skin entry site: 18–22G needle advanced into pleural fluid. Angle over the superior border of the rib to avoid inadvertent neurovascular injury.
•Complications: pneumothorax (when blind, 1–3%).
Usually if respiratory compromise from a large effusion. Similar technique as above, but place a 7–10Fr catheter. Potential risk of expansion pulmonary oedema if evacuate in excess of 2–3L or aspirate both lungs in one sitting. Also potential for pneumothorax—always obtain post-aspiration CXR.
True +ve rate of 90–95%. False +ve results usually related to malplacement of biopsy needle, necrotic tumour. Contraindications (relative) include severe COPD, pulmonary hypertension, coagulopathy, and contralateral pneumonectomy. Tumour seeding is extremely rare (1:20,000).
Complications include pneumothorax (25%, of which 5–10% need a chest tube) and haemoptysis (3%).
Density should be equal; the left is higher than the right by 5–15mm. If more disparity, consider elevation due to fibrosis (e.g. TB, radiotherapy) or depression by lobar or segmental collapse. Hilar enlargement may be vascular (e.g. pulmonary arterial or venous hypertension) or due to lymphadenopathy (e.g. sarcoidosis, lymphoma, or TB). Hilar calcification is seen in silicosis, sarcoidosis, and treated lymphoma.
•Enlarging pneumothorax on subsequent CXR.
•Poor lung function of contralateral lung disease.
Either:
1 Second to fourth anterior intercostal space, mid-clavicular line, or
2 Sixth to eighth intercostal space; mid-axillary line or posterior.
Use 8–12Fr catheters using a trocar technique. After the lung is fully re-expanded for 24h, the catheter is placed on a water seal for 6h and then removed if no residual pneumothorax.
Lung opacities may be subdivided into several basic patterns.
Air space shadowing: ill-defined, non-segmental, and with air bronchograms. No associated volume loss. Large variety of causes:
•Fluid → pulmonary oedema (cardiogenic and non-cardiogenic).
•Haemorrhage → trauma, coagulopathies, pulmonary haemosiderosis.
•Cells → pulmonary alveolar proteinosis, sarcoidosis, bronchoalveolar cell carcinoma, lymphoma, and infection (bacterial, fungal, and viral).
Linear opacities: associated obscuration of vessels and late appearance of CXR signs:
•Extrinsic allergic alveolitis.
•Malignancy (lymphangitis carcinomatosis).
Characterize according to their size and distribution:
•Granulomata (TB, histoplasmosis, hydatid).
•Immunological (Wegener’s, RhA).
•Inhalational (progressive massive fibrosis (PMF), Caplan’s syndrome).
•Mass or nodule with spiculated or irregular borders.
•Unilateral hilar enlargement or mediastinal widening.
•Cavitating nodule with thick rind of soft tissue.
•Cavitation commonest in squamous cell carcinoma (SCC).
•Malignancy can simulate air space disease (e.g. bronchoalveolar carcinoma, lymphoma).
•Interstitial patterns (lymphangitic spread of disease).
•Hilar and mediastinal adenopathy.
•Metastatic disease (including to ipsilateral or contralateral lung parenchyma).
Corne J, Carroll M, Delaney D.Chest X-ray Made Easy, 2nd edn. Edinburgh: Churchill Livingstone, 2002.
Hansell DM, Lynch DA, McAdams HP, Bankier AA.Imaging of Diseases of the Chest, 5th edn. London: Mosby, 2010.
Lobar collapse may be complete or incomplete. The commonest cause is obstruction of a central bronchus. The 1° signs are opacification due to lack of aeration and displacement of the interlobar fissures. Typical patterns of lobar collapse are illustrated in Fig. 13.7.
•Elevation of the hemidiaphragm (more prominent in lower lobe atelectasis than upper).
•Mediastinal displacement (tracheal displacement with upper lobe and cardiac displacement with lower lobe atelectasis).
•Hilar displacement more prominent with upper lobe atelectasis than lower.
•Crowded vessels in the affected lobe.
•Compensatory hyperinflation of remaining lung.
•In a normal CXR, the interface between the diaphragm and the mediastinum are visible due to a difference in density between the lung and these structures.
•The silhouette sign refers to loss of normal interfaces, implying there is opacification due to consolidation (the commonest cause), atelectasis, or a mass in the adjacent lung.
•Silhouetting helps to localize the site of the pathology, and both pleural and mediastinal disease produce the silhouette sign (see Table 13.4).
Table 13.4 Localization using the silhouette sign
| Interface lost | Location of lung pathology |
| SVC | Right upper lobe |
| Right heart border | Right middle lobe |
| Right hemidiaphragm | Right lower lobe |
| Aortic knob/left superior mediastinum | Left upper lobe |
| Left heart border | Lingula |
| Left hemidiaphragm | Left lower lobe |
Fig. 13.7 (a) Left upper lobe collapse. (b) Left lower lobe collapse. (c) Right upper lobe collapse. (d) Right middle lobe collapse. (e) Right lower lobe collapse.
↑ of the cardiothoracic ratio beyond 50% is considered abnormal if the P-A film is of good quality.
•Cardiomegaly (hypertrophy or dilatation of cardiac chambers).
•Pericardial effusion (globular heart).
•Poor inspiratory effort/↓ lung volumes.
The location of cardiac valves may be relevant when determining the location of calcification. On a lateral projection, draw a line from the xiphisternum to the carina and divide the heart into thirds. The location of the cardiac valves will be as demonstrated in Fig. 13.8.
Fig. 13.8 Schematic diagram showing the relations of the cardiac valves on a lateral film of the chest.
Figure 13.9 shows a P-A view. The right cardiac margin comprises three segments:
The left cardiac margin comprises four segments:
•Aortic arch (AA) (becomes more prominent with age).
•Main PmA at level of the left main stem bronchus.
•Left atrial appendage (may not be visible in normal hearts).
•RV is not usually seen in frontal projection.
•Tip of the ETT should be above the carina and below the thoracic inlet.
•The inflated cuff should not bulge the tracheal wall.
•Neck position can change the impact location of the tip.
•In neutral: the tip should be 4–6cm above the carina.
•Flexed: moves the tip inferiorly by 2cm.
•Extended: moves the tip superiorly by 2cm.
•Complications: malpositioned results in atelectasis or collapse due to bronchial obstruction. Tracheomalacia if over-inflated cuff; tracheal rupture may result in pneumothorax.
•Pearl: in situations where there is low pulmonary compliance (e.g. acute respiratory distress syndrome (ARDS)), a tip position closer to the carina may reduce barotrauma.
•Tip should be in the stomach.
•Tip and side port should lie distal to the oesophagogastric junction and proximal to the gastric pylorus.
•Potential complications include placement in airway or gastric/duodenal erosion.
•Tip should be located in the left or right PmA within 1cm from the hilum. Loops in the RA or RV may cause arrhythmias. There are two types of Swan–Ganz catheters:
1Used to measure wedge pressure.
2With an integrated pacemaker.
•Complications include pulmonary infarct, haemorrhage, PmA pseudo-aneurysm, and infection. If the tip is distal to the proximal interlobar PmA, there is a potential risk of PmA rupture or pseudo-aneurysm.
•Should be located in the RAt.
•Typically anchored in the anterior mediastinum. Multiple wires may be present and usually exit through the anterior chest wall.
•Newer systems have intraventricular electrodes with pin sensors.
•Tip should be located just distal to the origin of the left subclavian artery and be 2–4cm below the aortic knuckle.
•Complications include aortic dissection, low position associated with mesenteric or renal ischaemia, and high position with CVA.
•Tip should end in the lower SVC or the cavoatrial junction below the anterior first rib. Azygos malposition is seen in 1% and is associated with risk of venous perforation or catheter-associated thrombosis.
•Typical position should be in the apex of the RV. Can be located in the atrial appendage for atrial pacing and in the coronary sinus for atrial left ventricular pacing.
•Complications include electrode displacement, perforation, infection, or venous thrombosis.
•Side port should lie within the thoracic cavity.
•Tip of tube should not abut the mediastinum.
CT is very sensitive at:
•Detecting and quantitating calcification in coronary arteries.
•Non-invasively depicting the entire coronary tree.
•Determining the luminal diameter.
Improved hardware has resulted in less blooming artefact which could potentially overestimate the degree of stenosis seen with calcified plaques. It is very sensitive to haemodynamic stenosis (>50% of the luminal diameter). Multiple meta-analyses have shown NPV in high 90s.
For calcium scoring, the examination is performed without IV contrast and there are various algorithms available that provide a measure of the total coronary plaque burden. ECG gating is used to minimize cardiac motion; the type of gating employed has significant impact on patient radiation dose.
Also has potential for non-invasive diagnosis of coronary artery disease. The in-plane image resolution for current MR techniques is about 0.5mm, sufficient for assessment of large coronary vessels as well as in venous grafts following coronary artery bypass grafting, but inadequate for detecting disease in smaller side branches.
Provides a high-resolution dynamic study using predominantly steady-state free precession (SSFP) and/or gradient echo cine sequences.
SSFP is a ‘white blood sequence’ that provides excellent contrast between the myocardium and the blood pool. It is suited to cardiac imaging due to its high temporal resolution and excellent contrast.
Cine MRI provides quantitative assessment of cardiac morphology and function. Real-time images can be used for subjective analysis when gating is poor. Tissue characterization is usually performed with double or triple inversion fast spin echo sequences. These ‘black blood’ sequences null signal from flowing blood.
First-pass contrast-enhanced perfusion MRI is performed pre- and post-vasodilator stress to assess myocardial perfusion. Delayed contrast-enhanced MRI is used to assess myocardial viability, inflammation, and fibrosis.
Miller SW, Abbara S, Boxt LB.Cardiac Imaging: The Requisites, 3rd edn. Mosby, 2009.
Raff GL, Abidov A, Achenbach S, et al. SCCT guidelines for the interpretation and reporting of coronary computed tomographic angiography. J Cardiovasc Comput Tomogr 2009; 3: 122–36.
•Evaluation of an abnormal finding on plain film.
•Staging of 1° or metastatic malignancies.
•Evaluation of suspected mediastinal or hilar mass.
•Detection of thromboembolic disease by CTPA (see Figs 13.10 and 13.11).
•Detection and assessment of aortic dissection.
•Distinguishing empyema from lung abscess.
•CT-guided percutaneous needle biopsy of focal lung lesion or mediastinal abnormality.
High-resolution computed tomography (HRCT) comprises thin section images that are reconstructed using a special algorithm.
•Evaluation of a diffuse lung disease (see Fig. 13.12).
•Characterization of a solitary pulmonary nodule.
•Lung disease in a patient with abnormal pulmonary function tests but apparently normal CXR (see Table 13.5).
Table 13.5 HRCT patterns of interstitial lung disease
BOOP, bronchiolitis obliterans organizing pneumonia; COP, cryptogenic organizing pneumonia; CWP, coalworker’s pneumoconiosis; DIP, desquamative interstitial pneumonia; IPF, idiopathic pulmonary fibrosis; LIP, lymphocytic interstitial pneumonitis; PCP, pneumocystis pneumonia.
Fig. 13.11 Sagittal reformatted image confirms the extent of the thrombus and its relationship to the lumen.
Interpretation of the AXR, like the CXR, requires experience. In order to make things slightly easier, we have provided a rough guide to the various bony, soft tissue, and gas shadows seen on a ‘typical’ AXR (see Fig. 13.13). Figure 13.14 provides a normal AXR for correlation with the diagram. Figure 13.15 shows diffuse sclerotic metastases.
Fig. 13.15 Diffuse sclerotic metastases in a patient with a prostatic carcinoma. Note the presence of bilateral ureteric stents.
The standard plain film is a supine AXR. Erect views have largely been superseded and in the acute setting have been replaced by the erect chest to show free subphrenic air. Furthermore, chest diseases, such as MI or pneumonia, may simulate an acute abdomen. If there is doubt regarding the presence of a pneumoperitoneum, consider a lateral decubitus film (displays as little as 1mL of air).
Suspected obstruction, perforation, renal colic, and toxic megacolon and bowel ischaemia.
None, but where abdominal pain is non-specific and not attributable to the conditions listed above, an AXR is unlikely to be helpful.
A normal patient will have variable amounts of gas in the stomach, small bowel, and colon. You can identify the stomach as it lies above the transverse colon, has an air–fluid level in the erect view, and has rugae in its lumen. Large bowel calibre is variable; 5.5cm is considered the upper limit for the transverse colon in toxic megacolon and 9cm for the caecum in obstruction. Short fluid levels are normal. Fluid levels are abnormal when seen in dilated bowel or if numerous. If the bowel is dilated, distinguish between small and large bowel by the features listed in Table 13.6. Thickening of the bowel wall may be seen in a variety of aetiologies, most notably ischaemia, but also in IBD.
Table 13.6 Distinguishing features between small and large bowel
| Small bowel | Large bowel | |
| Haustrae | Absent | Present |
| Valvulae conniventes | Present in jejunum | Absent |
| Number of loops | Many | Few |
| Distribution of loops | Central | Peripheral |
| Diameter of loops | 30–50mm | >50mm |
| Solid faeces | Absent | May be present |
| Maximum diameter | 3cm | 6cm (9cm in caecum) |
| Maximum fold thickness | 3mm | 5mm |
Causes of bowel dilatation include mechanical obstruction, paralytic ileus, or a localized peritonitis (meteorism), e.g. adjacent to pancreatitis or appendicitis (see Table 13.7).
Table 13.7 Distinguishing mechanical obstruction from a paralytic ileus
| Feature | Ileus | Obstruction |
| Bowel calibre | Normal or dilated | Dilated |
| Air–fluid levels | Same level in a single loop | Differential levels (stepladder) |
| Other distinguishing features | Air seen throughout the GIT (diffuse ileus) or in localized ileus may be confined to a short segment | Distension seen to level of transition. Beyond this level, no air in bowel |
•Gas in the peritoneal cavity: look for air under the hemidiaphragm, outlining the falciform ligament or both sides of the bowel wall (Rigler’s sign). If there is any doubt, consider a lateral decubitus film. Causes include perforation (ulcer, neoplasm), post-operative, following peritoneal dialysis, or tracking down from the mediastinum.
•Air in the biliary tree: following sphincterotomy, gallstone ileus, or following anastomosis of the CBD to the bowel. This has a linear morphology and is seen centrally within the liver.
•Portal vein gas: pre-morbid sign in the context of bowel infarction, but less sinister in neonates with necrotizing enterocolitis (NEC) or following umbilical catheterization. In contrast to air in the bile ducts, its location is peripheral.
•Intramural gas: linear streaks of air in the bowel wall again usually a sinister finding implying ischaemia, but may be seen due to benign causes such as in patients with COPD where its configuration is more rounded and cystic (pneumatosis cystoides).
•Air in the retroperitoneum: delineates the renal shadows and psoas muscle; common causes are trauma, iatrogenic (e.g. after colonoscopic perforation), and after perforation of a duodenal ulcer.
•Gas in an abscess: look for displacement of adjacent bowel and an air–fluid level. Other causes include air in the urinary tract and within necrotic tumours. In this scenario, the gas is mottled and does not display features consistent with bowel.
•Look for any soft tissue masses or ascites: the latter is detectable on plain films if gross. There will be displacement of the ascending and descending colon from the side walls, with loops of small bowel seen centrally.
•Look for abdominal or pelvic calcification: firstly, localize the site. This may require another view. The vast majority are clinically insignificant, i.e. vascular calcification, pelvic phleboliths, and calcified mesenteric nodes. In the abdomen, there may be pancreatic calcification (chronic pancreatitis) or hepatic calcification (old granulomata, abscesses, or less commonly hepatomas and metastases from mucinous 1°s). Gallstones are less commonly calcified and may contain central lucency (e.g. Mercedes Benz sign), whilst renal and ureteric calculi commonly calcify. Renal tumours and cysts rarely calcify, and more widespread renal calcifications may be seen in nephrocalcinosis due to a wide variety of causes. In the pelvis, ovarian calcifications (less common with malignant masses and seen more often in association with benign pathologies such as dermoids) is uncommon, whilst uterine calcifications due to fibroids commonly occur. Bladder wall calcifications may be seen with bladder tumours, TB, and schistosomiasis. Prostatic calculi and calcifications are common and of no significance. Vas deferens calcifications is seen in patients with diabetes.
•Soft tissues: look at renal outlines (normally smooth and parallel to the psoas; should be between 2–3 vertebral bodies). Absence of psoas margins may indicate retroperitoneal disease and haemorrhage.
•Bones of the pelvis and lumbar spine: look for OA, metabolic bone disease (hyperparathyroidism, sickle-cell anaemia), the rugger jersey spine of osteomalacia, and Paget’s disease ( Spinal imaging, pp. 836–837; Pelvis, p. 838). Bony metastases may be lytic or sclerotic.
Barium suspension is made up of small particles of barium sulfate in a solution. Due to its high atomic number, it is highly visible on X-rays. The constituents of individual suspensions vary, depending on the part of the GIT being examined. The particles are coated to improve flow and aid mucosal adhesion. When made up, it comprises a chalky (sometimes unpalatable!) suspension. Advantages include low cost, easy availability, and good assessment of the mucosal surface.
•Perforation: if leakage occurs into the peritoneal cavity, it can produce pain and hypovolaemic shock (50% mortality). Long-term sequelae include peritoneal adhesions.
•Aspiration: in small amounts, unlikely to have any clinical significance, but if pre-existing respiratory impairment or aspiration of larger amounts (i.e. more than a few mouthfuls), the patient will need physiotherapy.
•Obscuration: CT examination in the presence of a recent barium examination will result in a poorly diagnostic study, as high-density barium results in streak artefacts.
•Barium impaction: rarely may exacerbate obstruction if barium collects and is concentrated above a point of obstruction.
These are more expensive and provide inferior coating and contrast. They include iodinated agents such as Gastrografin®.
•Suspected perforation, especially into the peritoneal cavity.
•To opacify bowel during CT examinations.
Risks include pulmonary oedema if aspirated and hypovolaemia, especially in children. Both are a result of hyperosmolar effects. If aspiration is likely, use water-soluble non-ionic contrast, which causes less shift of body fluid compartments. Non-ionic contrast should be used in all infants (especially neonates) and preoperative patients requiring water-soluble contrast.
(See Table 13.8.)
For studies other than when barium is being utilized, the contrast media are non-ionic iodinated agents that are given PO, endoluminally, or IV. Non-ionic contrast agents are higher in cost than their ionic counterparts (rarely used currently) but have a lower incidence of adverse reactions (by a factor of 9 for severe reactions). They are typically excreted by glomerular filtration. Half-life is dependent on the dose given, distribution, and renal function. Contrast reactions can be idiosyncratic or anaphylactoid or non-idiosyncratic.
High-risk patients are those with prior contrast reactions, a history of allergy or atopy, sickle-cell disease, phaeochromocytoma, and multiple myeloma (to name a few). Contrast-induced nephropathy is commoner if creatinine is elevated at time of administration or if the patient has a pre-existing renal impairment, e.g. DM.
Pre-medication can be administered to patients with prior contrast reactions. Protocols vary but typically include a corticosteroid and an antihistamine. Consider the use of alternate modalities if risk is high, e.g. USS or MRI, instead of CT with contrast.
Extravasation of contrast is typically treated symptomatically with ice pack and elevation. Plastic surgery consult should be obtained if concern regarding compartment syndrome in patients who have in excess of 100mL in extremity or severe pain/discoloration or altered perfusion.
Gadolinium is an MR-based contrast agent that is paramagnetic. It is also excreted by glomerular filtration.
Its safety profile is favourable in that it does not have any of the nephrotoxicity associated with the iodinated contrast media and is more commonly associated with minor reactions such as headaches. Since 2006, there is an established association between the use of gadolinium-containing contrast agents and NSF. NSF involves fibrosis of the skin, joints, eyes, and other viscera. Subsequent to this finding, the use of gadolinium is contraindicated in patients with an eGFR of under 60 and particularly if below 30.
Table 13.8 Pharmacological agents used in barium studies
Plain films do not usually demonstrate the oesophagus, unless it is very distended, e.g. achalasia. They may be useful in identifying an opaque foreign body within the lumen. The barium swallow is the usual contrast examination to visualize the oesophagus (see Fig. 13.16). Rapid-sequence films are taken with a fluoroscopy unit, whilst the patient swallows barium (usually in an erect position). Films are taken in an AP and oblique projection (to throw the oesophagus clear of the spine), with the oesophagus distended with barium (to demonstrate its outline) and empty to show the mucosal folds.
The oesophagus commences at C5/6. There are normal indentations on its outline by the cricoid cartilage, aortic arch, left main bronchus, and left heart.
These include the assessment of dysphagia, pain, reflux disease, tracheo-oesophageal fistulae (in children), and post-operative assessment where there has been gastric or oesophageal surgery.
No absolute contraindications exist, but in all barium studies, the quality of the study relies heavily on patient co-operation, and therefore immobile patients who are unable to weight-bear may only be suitable for limited studies. The post-operative oesophagus is usually assessed with Gastromiro® or a non-ionic contrast.
•Diverticulae: these include pharyngeal pouches (a midline diverticulum), traction diverticulae (due to adhesions), or pseudodiverticulae; dilated mucous glands seen in reflux or infective oesophagitis.
•Luminal narrowing: strictures may be benign (e.g. oesophagitis—shown in Fig. 13.17, scleroderma, pemphigus, corrosives, or infection) or malignant.
•Webs: mucosal structures, which may be seen anywhere in the oesophagus; seen with skin lesions, e.g. epidermolysis or pemphigus, GVHD, and Plummer–Vinson syndrome.
•Mega-oesophagus: can be with associated obstruction, as in malignant strictures, or without as in achalasia, diabetic neuropathy, or Chagas’ disease (see Fig. 13.18a–c).
•Ulceration/oesophagitis: may be due to GORD, infection, corrosives, or iatrogenic. Findings include lack of distensibility, fold thickening, and mucosal irregularity.
•Oesophageal tears: spontaneous, neoplastic, post-traumatic, iatrogenic, and following prolonged emesis. Look for pneumomediastinum, left pleural effusion, and features of mediastinitis.
•Filling defects: foreign bodies, varices (proximal due to SVC obstruction), distal (in association with portal hypertension), neoplasms that may be benign (as in leiomyoma) or malignant. Most commonly SCC (95%).
•Fold thickening: may be due to oesophagitis, varices, or infiltration by lymphoma.
•Air–fluid level: commonest in hiatal hernias, but also seen with a pharyngeal pouch.
Fig. 13.16 Lateral oblique projection during a barium swallow series shows a feline oesophagus. This can be a normal variant but is often associated with GORD.
About 200mL of a high-density (85% w/v barium sulfate), low-viscosity barium is used for a double contrast study, which gives good coating without obscuration of mucosal detail. An effervescent agent is given to provide adequate luminal distension. The gastric mucosa is characterized by rugae (parallel to the long axis, 3–5mm thick) and area gastricae (nodular elevations, 2–3mm wide). The patient is fasted for about 6h to avoid food residue, which may cause diagnostic uncertainty. The techniques for coating the stomach and projections are variable. A smooth muscle relaxant may be given as part of the routine, particularly to assess the pylorus and duodenum.
Dyspepsia, weight loss, abdominal masses, iron deficiency anaemia of uncertain cause, partial outlet obstruction, and previous GI haemorrhage.
Complete large bowel obstruction.
•Filling defects: these may be intrinsic or extrinsic. Carcinoma remains the commonest cause of a filling defect in an adult (irregular, shouldered with overhanging edges). If there is antral involvement, there may be associated outlet obstruction. Diffuse mucosal thickening and failure to distend is seen with linitis plastica. Other causes include gastric lymphoma, polyps (histology difficult to predict), and bezoars. Smooth filling defects are seen in conjunction with leiomyomas, lipomas, and metastases. Extrinsic indentation by pancreatic tumours or an enlarged spleen may cause an apparent filling defect.
•Fold thickening (>5mm): seen in association with hypersecretion states such as Zollinger–Ellison syndrome, gastritis, and Crohn’s disease. It may also be 2° to infiltration by carcinomas, lymphomas, or eosinophilia.
•Outlet obstruction: may be diagnosed by failure of the stomach to empty <50% of the barium ingested at 4h. This may be seen in carcinomas, but also in scarring caused by chronic duodenal ulceration.
•Hiatal hernia: herniation of the stomach into the chest occurs via the oesophageal hiatus in the diaphragm. There are two types—in a sliding hernia (commoner), there is incompetence of the sphincter at the cardia, often associated with reflux. Other sequelae include oesophagitis, ulceration, or stricture. In a rolling hernia, the fundus herniates through the diaphragm, but the gastro-oesophageal junction remains competent and lies below the diaphragm.
•Gastritis and ulceration: gastritis is characterized by small, shallow barium pools with surrounding lucent rings due to oedema. There are features that may be used to distinguish benign from malignant ulcers on barium studies. Ulcers are seen either as a crater or as a projection from the luminal surface (see Fig. 13.19). Benign ulcers are commonly seen on the lesser curve with smooth radiating folds, which reach the edge of the ulcer crater. Malignant lesions may have an associated mass and have a shallow crater and an irregular contour. With the ease of availability of endoscopy, the use of barium meals in diagnosing ulceration has declined. Endoscopy has the advantage of being able to diagnose gastritis more accurately, assess ulcer healing, make a histological diagnosis, and more accurately assess the post-operative stomach. However, early assessment of the post-operative stomach is radiologically performed to exclude complications such as anastomotic leaks. A water-soluble contrast agent is preferred in the early post-operative phase.
Small bowel studies are performed for indications such as occult bleeding, recurrent obstructive symptoms, and malabsorption, and to confirm and define the extent of small bowel disease in Crohn’s.
•Small bowel follow-through: the patient drinks 200–300mL of barium (with metoclopramide to speed transit time). The single contrast column is followed by films at regular intervals until the barium reaches the colon. Transit time is variable, but the entire process may take 1–6h, depending on the adequacy of bowel preparation. Films are taken at intervals of ~20min initially, in the prone position, which aids separation of the loops. When the barium reaches the caecum, spot views of the terminal ileum are taken.
•Small bowel enema (enteroclysis): this technique provides better demonstration of mucosal detail, as there is rapid infusion of a continuous column of barium directly into the jejunum. Methylcellulose is administered following the barium to provide double contrast. This is achieved via a weighted nasogastric tube which is positioned at, or distal to, the duodenojejunal (DJ) flexure. Disadvantages include poor patient tolerance (related to intubation) and a relatively high screening dose.
Both techniques require the patient to be on a low-residue diet beforehand.
The indications are the same for both techniques and include pain, diarrhoea, bleeding, partial obstruction, malabsorption, overgrowth syndromes, assessment of Crohn’s disease activity and extent, and suspected masses. The small bowel enema may be preferred for assessment of recurrent Crohn’s disease or complex post-operative problems, but the small bowel follow-through is otherwise routinely used.
Complete obstruction and suspected perforation.
The small intestine measures ~5m and extends from the DJ flexure to the ileocaecal valve. The proximal two-fifths is the jejunum; the distal three-fifths is the ileum. Normal calibre is 3.5cm for the jejunum and 2.5cm for the ileum (up to 1cm more on enteroclysis). The valvulae conniventes are circular in configuration, and ~2mm thick in the jejunum and 1mm thick in the ileum (see Fig. 13.20).
•Dilatation is indicative of malabsorption, small bowel obstruction (SBO), or paralytic ileus. There may be accompanying effacement of the mucosal pattern. When seen with fold thickening, it may be due to Crohn’s, ischaemia, or radiotherapy. Mucosal thickening may be due to infiltration by lymphoma or eosinophilia, adhesions, ischaemia, or radiotherapy.
•Strictures are seen in Crohn’s disease and lymphoma. There is usually dilatation of the bowel proximally. Crohn’s disease causes skip lesions, ulceration, strictures of variable length, and a high incidence of terminal ileal involvement. There may be associated ulceration, fold thickening, and fistulation (see Fig. 13.21).
•Malabsorption: radiological investigation may reveal an underlying structural abnormality. The findings in malabsorption include dilatation, fold thickening, and flocculation of barium.
This is a hybrid technique that combines fluoroscopic intubation and small bowel infusion with an abdominal CT. This can be performed with +ve enteral contrast or neutral enteral contrast.
The advantage of this technique is that both intra- and extraluminal/extra-enteric information is obtained, rendering it superior to many of the per-oral small bowel studies. Disadvantages include the minimally invasive nature and the radiation associated with a CT examination. CT enteroclysis is complementary to capsule endoscopy in the elective investigation of small bowel disease and should be particularly considered in Crohn’s disease, small bowel obstruction, and unexplained GI bleeding. There has been a paradigm shift to CT enterography for the assessment of small bowel disease. This is most relevant in the IBD population who are on disease-modifying drugs.
Fig. 13.20 A 30min film in a small bowel follow-through series showing a normal mucosal fold pattern.
Fig. 13.21 Small bowel enema showing at least two strictures (arrows) in this patient with Crohn’s disease. Compare the mucosal detail with the small bowel follow-through.
This is the 1° modality for assessment of the biliary tree and for exclusion of pancreatic pathology. With the current scanner resolution, the sensitivity for stone disease is in the range of >95% for stones exceeding 2mm in diameter. For choledocholithiasis (stones in the CBD), the sensitivity falls to around 50%, and MRCP or ERCP is more helpful.
This is rarely performed but may be useful in patients with biliary symptoms post-cholecystectomy or with a non-functional gall bladder. It is contraindicated in the presence of severe hepatorenal disease, as the side effects related to the contrast media are considerable. CT cholangiography uses a similar contrast agent but offers the advantage of cross-sectional assessment of the bile ducts. It is often used when MRCP has not helped delineate the anatomy in donors prior to liver transplantation or when MR is contraindicated or simply not available.
The biliary and pancreatic ducts are directly filled with contrast, following endoscopic cannulation and during X-ray screening. This has both a diagnostic and therapeutic role. It is particularly of value in the demonstration of ampullary lesions and to delineate the level of biliary tree obstruction in patients with obstructive jaundice. It allows sphincterotomy to be performed to facilitate the passage of stones lodged in the CBD.
The biliary tree is directly injected with contrast, following percutaneous puncture of the liver. This is both diagnostic in defining a level of obstruction and therapeutic in biliary duct obstruction, as it may be used as a precursor to a biliary drainage procedure or prior to insertion of a stent. Contraindications include bleeding diatheses and ascites.
•Per-operative cholangiogram: in which the CBD is filled with contrast during cholecystectomy to exclude the presence of CBD stones.
•T-tube cholangiogram: after operative exploration, a T-tube is left in the CBD for a post-operative contrast study to exclude the presence of retained stones.
•MRCP: this is a non-invasive technique where heavily T2-weighted (T2W) images are obtained without contrast administration. The bile acts as an intrinsic contrast agent, and stones are visualized as filling defects. The entire biliary and pancreatic ductal system can be visualized (see Fig. 13.22). Common indications for this technique include unsuccessful ERCP, a contraindication to ERCP, as well as evaluation of the post-surgical biliary tree.
•Allows better visualization of the ducts proximal to the level of obstruction.
•When combined with conventional sequences, allows detection of extraductal disease.
•↓ spatial resolution for peripheral intra-hepatic ducts and for pancreatic ductal side branches (e.g. as in pancreatitis).
•Subtle ductal lesions may be difficult to appreciate, as ducts are imaged in the non-distended physiological state.
•Inability to perform therapeutic endoscopic or percutaneous intervention of obstructing bile duct lesions.
•MRCP is comparable with ERCP in the detection of obstruction, with a sensitivity and specificity of 91 and 100%, respectively.
•Causes of filling defects are usually stones, air, tumours, blood, or sludge.
Contrast-enhanced MRCP can also be performed with fat-saturated T1-weighted (T1W) imaging after injection of gadolinium contrast agents that have biliary excretion. These cause TI hyperintensity with bile but require a 20–45min delay prior to imaging to allow for biliary excretion.
Fig. 13.22 Heavily T2-weighted slab image showing an irregular beaded pancreatic duct in this patient with chronic pancreatitis. There is a small pseudocyst in the tail (arrowhead).
US is the modality of choice for initial screening, whether assessing the parenchyma for diffuse disease or trying to evaluate and/or characterize focal liver lesions. Although US is sensitive in depicting focal lesions, it is not specific and there can be overlap in the imaging characteristics of benign and malignant lesions. CT, and particularly MRI, are more tissue-specific in characterizing liver lesions. The liver is supplied predominantly by the portal venous system (80%). On CT, the differing phases of enhancement are utilized to assess a lesion.
Arterial phase images (20–30s after injection) ↑ the conspicuity of lesions that are hypervascular such as hepatocellular carcinoma or focal nodular hyperplasia. Portal venous phase images are acquired at 50–70s and provide maximum enhancement of background hepatic parenchyma. Lesions that are relatively hypovascular on this phase stand out such as metastases.
Delayed imaging (equilibrium phase) minutes after contrast administration allows lesions that demonstrate relative washout of contrast (i.e. appear hypo-attenuating) relative to background liver, such as hepatocellular carcinomas, to stand out. Lesions that are relatively fibrotic (e.g. in tissue content or scars) conversely exhibit ↑ enhancement on delayed images.
MRI displays the same patterns of contrast enhancement but has superior lesion-to-liver contrast and imparts no ionizing radiation. Multiple dynamic post-contrast sequences can thus be obtained. Tissue characterization allows for detection of intralesional lipid (as in adenomas), and advanced techniques such as diffusion-weighted imaging (DWI) improve sensitivity for lesion detection.
Further characterization of lesions can be obtained by hepatocellular-specific MRI contrast agents which allow definitive assessment of lesions with hepatocytes such as focal nodular hyperplasia (FNH), precluding the need for biopsy.
This is used for evaluation of the large bowel. Increasingly, many institutions are replacing this technique with CT colonography (CTC; Virtual colonoscopy, p. 807) or conventional CT, depending on the clinical indication. Barium is run into the colon under gravity via a tube inserted into the rectum. The column of barium is followed by air (room air or CO2) to achieve double contrast. The CO2 is better tolerated and more readily absorbed. Hyoscine butylbromide (a smooth muscle relaxant) may be given to minimize spasm and optimize mucosal relief. Bowel preparation prior to the examination (low-residue diet and aperients) is vital to ensure that there is no faecal material, which may mask mucosal abnormalities or be mistaken for small polyps. Remember the examination is uncomfortable and requires reasonably good patient co-operation and mobility.
► Do not request this in frail or elderly patients, unless there is a good clinical indication.
A rectal examination or sigmoidoscopy is essential to avoid abnormalities being missed.
If evaluation of the colonic mucosa is not the 1° aim, then a single contrast technique will suffice. This is applicable in children where the patient is unco-operative and where gross pathology is being excluded, and in the evaluation of obstruction/volvulus or in the reduction of an intussusception.
Change in bowel habit, iron deficiency anaemia, abdominal pain, palpable mass of suspected colonic origin, and weight loss of unknown cause.
Suspected perforation, recent rectal biopsy, toxic megacolon, or pseudo-membranous colitis.
•Solitary filling defect: polyps are classified according to histology. The commonest are hyperplastic (no malignant potential; adenomatous polyps are premalignant with the risk of malignancy ↑ with size (<5mm = 0%, >2cm = 20–40%). Also found are adenocarcinoma (↑ risk in ulcerative colitis, polyposis syndromes, villous adenoma) and less commonly metastases and lymphoma.
•Multiple filling defects: polyps (polyposis syndromes or post-inflammatory pseudopolyps), pneumatosis coli, metastases, and lymphoma.
•Ulceration: IBD, ischaemia, infection, radiation, and neoplasia.
•Colonic narrowing: neoplasms (apple core lesion), metastases, lymphoma, diverticular disease, IBD, ischaemia, and radiation.
•Dilatation: mechanical, e.g. proximal to neoplasm, volvulus or non-mechanical, post-operative ileus, metabolic, and toxic megacolon.
•Diminished haustration: cathartic colon, IBD, and scleroderma.
•↑haustration (thumbprinting): ischaemia, haemorrhage, neoplasm, and IBD.
•Widening of the pre-sacral space (>1.5cm at S2): normal in up to 40%, but also seen in association with IBD, neoplasms, infection, and sacral/pelvic lipomatosis.
Remains a complementary technique and has the advantage of being both therapeutic and diagnostic (e.g. biopsy, polypectomy, etc.). In elderly patients, CT with prior bowel preparation and air insufflation is less invasive and less arduous.
Helical CT images of distended colon taken during a breath-hold are used to obtain 2D or 3D images of the colon. Images are acquired in the supine and prone positions to assess lesional mobility (and thus distinguish stool from polyps). No IV contrast is administered for routine screening studies, and the examination is often performed utilizing a low-dose technique. Recent studies using 1° 3D interpretation, as well as national studies, such as the ACRIN II trial, have shown sensitivities in the range of 94% for polyps of at least 1cm in diameter and around 88% for lesions measuring at least 6mm. Current refinements in this technique include the use of computer-assisted detection (CAD) to improve performance, as well as the use of prepless techniques (i.e. the patient does not have to undergo prior bowel cleansing).
(See Figs 13.23 and 13.24.)
Fig. 13.23 Standard supine projection from a double contrast barium enema (DCBE) showing a normal large bowel.
Pickhardt PJ, Choi JR, Hwang I, et al. Computed tomographic virtual colonoscopy to screen for colorectal neoplasia in asymptomatic adults. N Engl J Med 2003; 349: 2191–200.
•Look for any urinary tract calcification: 90% of stones are radio-opaque. Other causes include hyperparathyroidism, medullary sponge kidney, and RTA.
•Renal outline: between T12 and L3 and 10–15cm. Left bigger and higher than the right.
•Assess bones of spine and sacrum: for bony metastases or spina bifida (may be relevant in enuresis).
This provides a good overview of the urinary tract and, in particular, the pelvicalyceal anatomy. Fluid restriction and laxatives are no longer necessary and, in particular, the former is to be avoided in diabetics, renal failure, and myeloma. Following the preliminary plain film, 300mg/kg of contrast media is injected IV. The film sequence is varied according to the clinical scenario. An immediate film shows the nephrogram phase and displays the renal outlines. An increasingly dense delayed nephrogram is seen in acute obstruction, acute hypotension, ATN, and renal vein thrombosis. A faint persistent nephrogram is seen with acute glomerulonephritis and it may be delayed in RAS. Later films show the pelvicalyceal systems (pyelogram), ureters, and bladder.
(See Fig. 13.25.)
•Loss of renal outline: congenital absence, ectopic kidney, tumour, abscess, or post-nephrectomy (look for absent twelfth rib).
•Small kidney (unilateral): ischaemia (RAS), radiation, or congenital hypoplasia.
•Small kidney (bilateral): atheroma, papillary necrosis, or glomerulonephritis.
•Large kidney (unilateral): duplex, acute pyelonephritis, tumour, or hydronephrosis.
•Large kidney (bilateral): polycystic kidneys and infiltrative disease such as myeloma, amyloid, and lymphoma. Acute inflammation such as glomerulonephritis, ATN, and collagen vascular disease.
•Pelvicalyceal filling defect: smoothly marginated (clot, papilloma), irregular margins (tumour, e.g. renal cell or transitional carcinoma), intraluminal (sloughed papilla, calculus, or clot), extrinsic (vascular impression or cyst), irregular renal outline (scarring, e.g. in ischaemia, TB, pyelonephritis, or reflux nephropathy).
•Dilated ureter: >8mm in entire length. May be due to obstruction (functional as in 1° megaureter) or mechanical stenosis as in ureteric or urethral stricture and in reflux disease.
•Ureteric stricture: wide differential; determine the length. Differentials include tumour (transitional cell carcinoma, metastatic), inflammatory (TB, schistosomiasis), congenital, trauma (radiation or iatrogenic).
•Deviated ureters: normal course of ureters in close proximity to transverse processes of vertebral bodies.
•Lateral deviation: seen with retroperitoneal nodes, tumours, and aortic aneurysm.
•Medial deviation: posterior bladder diverticulum, retroperitoneal fibrosis (can be idiopathic or related to various aetologies, including malignancy.
CT is the preferred method for assessment of many pathologies within the genitourinary (GnU) tract, including trauma, complex infections, renal and adrenal masses, neoplastic disease, retroperitoneal processes, renovascular hypertension, and in renal colic.
In many institutions, IVU has been replaced by its CT counterpart (CT urography (CTU)). MDCT has had an impact on slice thickness and speed of scanning, such that the urinary tract mucosa can be assessed in exquisite detail. Depending on institutional protocol, the examination is performed as a 2- or 3-part study. Typically, it includes a non-contrast phase (to assess for stones, acute blood) and then an excretory/delayed phase to assess the collecting systems and ureters. It has a high sensitivity (95%) in detecting upper urinary tract uroepithelial malignancies. Common indications for usage include:
•Haematuria (with −ve cystoscopy and USS having excluded parenchymal causes).
•Unexplained hydronephrosis on USS.
•Evaluation of the upper tract in patients with known lower urinary tract transitional cell carcinoma or following trauma or iatrogenic ureteric injury.
May be used as an alternative or complementary examination with IVU and may be used to:
•Demonstrate or exclude hydronephrosis, especially in ARF.
•Evaluate renal tumours, cysts, and abscesses.
•Follow up transplant kidneys and chronic renal disease.
•Assess renal blood flow using Doppler.
•Perform serial scanning in children with recurrent UTIs.
•Assess bladder morphology and volume, and the prostate.
•Provide guidance for interventional techniques, e.g. renal biopsy and nephrostomy placement.
CT is more accurate for staging renal tumours, assessing retroperitoneal pathology, staging bladder and prostatic tumours, and assessing renal vascular pathology (such as RAS). In many centres, unenhanced CT is replacing IVU as a gold standard for assessment of renal stone disease. It is more accurate at depicting stone burden than IVU and precisely demonstrating the level and cause of obstruction in the acute setting. Evaluation of ureteric pathology in the context of haematuria is also being performed with contrast-enhanced CT.
MRI is valuable in staging vascular involvement by renal carcinomas. Dedicated pelvic coils and endoluminal coils show excellent results in staging pelvic and gynaecological malignancies.
Following catheterization of the bladder, contrast is introduced till bladder capacity is reached. This is the technique of choice for defining the urethral anatomy and gauging the presence/degree of vesicoureteric reflux in children. It is also used if there are recurrent UTIs or suspected lower urinary tract obstruction.
Contrast is injected directly into the urethra in ♂ in the assessment of urethral trauma, strictures, and congenital anomalies such as hypospadias.
The ureters are catheterized (usually following cystoscopy in theatre) and contrast injected under X-ray screening. Of value in urothelial tumours and to define the site of obstruction, e.g. non-opaque calculi. Useful if IV techniques have failed to demonstrate the intra-renal collecting system or ureters due to impaired renal function or a high-grade obstruction.
A femoral approach with selective catheterization of renal vessels. Main uses include haematuria (look for AVMs), hypertension (RAS), in transplant donors (to define anatomy), and in renal cell carcinoma (where embolization is being contemplated).
Interventional radiology, pp. 844–847.
Breast cancer is a common problem (1 in 12 women). The average ♀ has a 1 in 8 chance of being diagnosed with breast cancer during her lifetime. Mammography is the first-line tool for detection of breast cancer; however, sensitivity of screening mammogram is variable and is influenced by variables such as density of breast tissue. Sensitivity is between 68 and 90% and is higher if the patient is symptomatic (93%).
Screening mammography detects 2–8 cancers per 1000 women screened. Since 1990, mortality from breast cancer has steadily declined, and this has been attributed to advances in adjuvant therapy as well as to mammographic screening.
Breast tissue has a narrow spectrum of inherent densities, and in order to display these optimally, a low-kilovoltage (kV) beam is used. It enhances the differential absorption of fatty, glandular, and calcific tissues. Dedicated mammographic units provide low-energy X-ray beams with short exposure times. The breast is compressed to minimize motion and geometric unsharpness. High resolution is paramount in order to detect microcalcification (as small as 0.1mm). The breast is a radiosensitive organ, so doses need to be kept to a minimum.
These are the mediolateral oblique (MLO) and craniocaudal (CC) views (see Fig. 13.26). The CC view is trans-axial. The MLO image plane is ~45–60° from the axial plane and parallels the pectoralis major. Adequacy of the lateral oblique view may be gauged by the pectoralis major muscle, which should be visible to the level of the nipple, inclusion of the axillary tail, and inclusion of the inframammary fold. The CC view detects posteromedial tumours that may be missed on the MLO view and is better at breast compression. Additional projections, such as true lateral, cleavage, exaggerated CC, spot compression, and magnification views, may be used to clarify abnormalities. These techniques provide better detail and disperse any overlapping tissue to avoid obscuration of lesions.
The breast parenchyma is made up of glandular tissue in a fibrofatty stroma. Cooper’s ligaments form a connective tissue network. The amount of glandular tissue ↓ with age; as it is dense on mammography, the suitability of the technique for detecting pathology ↑ with age.
•Adequacy of study; are additional views required?
•Adequate penetration of fibroglandular tissue.
•Skin, nipple, trabecular changes.
•Asymmetry (may be a normal variant).
Comparison with prior imaging is imperative, as changes can be subtle and progressive.
•There should be adequate tissue demonstrated on both CC and MLO views. The posterior nipple line is a line drawn from the posterior nipple to the pectoralis muscle. On each view, the posterior nipple line should be within 1cm of each other.
•Image should be free from blur and artefacts.
•Nipple should be in profile on at least one view.
•Blurring can cause benign calcification to look amorphous, and subtle calcification may be missed.
Fig. 13.26 CC mammographic view of the breast. The arrows depict a stellate mass consistent with a carcinoma.
•A mass with ill-defined or spiculate borders (see Fig. 13.27).
•Clustered, linear, or irregular calcification (which may occur in the absence of a mass).
•2° signs include distortion of adjacent stroma, skin thickening, and nipple retraction.
Ninety-four per cent of breast carcinomas is ductal in origin.
The breast imaging and reporting data system (BIRADS) is a standardized way of reporting mammography and includes a lexicon, a structured report, and clear categories for follow-up and reassessment of imaging findings.
This largely forms a modality for assessment, not diagnosis or detection, and is a valuable adjunct and problem-solving tool. It can be used to evaluate non-palpable masses and palpable masses not seen on mammography, to determine the internal architecture (solid vs cystic), to assess asymmetric density, to assess breast implants, and as a 1° imaging modality in young women (<35 years), as well as pregnant and lactating women. It is also used as a tool to guide intervention, i.e. drainage of cysts and biopsy of suspicious lesions.
MRI remains a problem-solving tool in breast imaging. Widespread implementation of MRI (for instance, for screening) is hampered by its low specificity (37–97%). It can ↑ the number of benign biopsies that are performed. This clearly has resource implications, as well as generating unnecessary patient anxiety. Both MRI and US may be used to evaluate implants and their integrity, but MRI is the only modality that is sensitive in the evaluation of intracapsular implant rupture. Contrast-enhanced MRI of the breast is also a sensitive method for detection of malignancy, with reported sensitivities in the region of 93%. It is especially useful to detect recurrent breast carcinoma and where conventional techniques are unable to help in the distinction from more benign lesions. Breast MRI is also being advocated for screening young patients with a family history/genetic risk of breast carcinoma.
Breast MRI is increasingly being used for staging breast carcinomas, to look for synchronous 1° lesions, and to evaluate the breast in patients found to have malignant nodes in the axilla. It can also be used to evaluate tumour response to neo-adjuvant chemotherapy. In problematic mammographic patients, it can be useful in distinguishing dense breast tissue or fibrosis from malignancy. In the post-operative setting, it can be used in patients with +ve surgical margins or to assess post-operative scar vs disease recurrence. The selection of pulse sequences and IV contrast administration is based on the clinical indication.
The patient lies prone on the scanner, and a specialized coil surrounds the breast. The entire scan varies in duration from 20min to 1h. Most protocols for exclusion of malignancy rely on a dynamic enhanced sequence. Cancers typically enhance more rapidly than benign lesions.
Fig. 13.27 Subtraction sagittal MR image of the breast following gadolinium, showing an enhancing spiculated mass consistent with malignancy.
US is a high-frequency mechanical vibration produced by piezoelectric materials, which have the property of changing thickness when a voltage is applied across them. It is an important cross-sectional modality and has widespread applications in the abdomen, neck, pelvis, and extremities. At diagnostic levels, there are no known damaging sequelae to tissues, and therefore it is safe for use in obstetrics, providing invaluable imaging of the developing fetus.
Probe selection is dependent on the area being imaged. Highe-frequency probes provide greater resolution but have limited depth of penetration and may therefore be suitable for assessment of superficial structures (e.g. extremity US, thyroid, testicular US). Doppler USS is based on the principle that sound reflected by a moving target has a different frequency to the incident sound wave. The frequency shift is proportional to the velocity of the flowing material. Doppler therefore not only enables detection but also quantification of velocity.
USS is cheap, readily available, and non-invasive, and has high patient acceptability. It has a wide range of applications as listed below. There are also no radiation implications. Again, advances in technology have resulted in vast improvements in the resolution of this modality, such that subtle pathology is more readily identifiable. The portability of USS also lends itself to use in the setting of emergency and critically ill patients, as well as providing guidance for intra-operative procedures.
None, but remember that USS is operator- and patient-dependent and should be used as a problem-orientated modality, not as a total body survey. It cannot be used to image air-containing structures or bone. The resolution of the USS image is inversely related to the depth of penetration. Therefore, image quality in obese patients is suboptimal.
•Head and neck: may be used for evaluation of the salivary glands, thyroid, lymph nodes, and palpable or clinically suspected masses. Doppler is used to assess the carotid vessels and quantify the degree of stenosis/occlusion.
•Chest (excluding breast): the use here is limited to palpable chest wall lesions, assessment of pleural abnormalities, biopsy, and drainage of pleural effusions, and is occasionally of use in directing a biopsy of peripheral lung or mediastinal masses.
•Abdomen and pelvis: this is the main use of USS. Useful for assessment of solid organs, e.g. kidneys, spleen, gall bladder (see Figs 13.28 and 13.29), liver (see Fig. 13.30), pancreas, uterus/adnexae, and bladder. A full bladder is used as an acoustic window in the pelvis. Retroperitoneal masses and lymph nodes may be visible, depending on patient habitus. USS is useful for directing biopsy of solid organs/masses and for drainage of ascites, abscesses, and collections.
•Limbs: musculoskeletal USS has been revolutionized by advances in high-frequency probes, which enable characterization of soft tissue masses, tendon-related pathology, rotator cuff lesions, masses, effusions, and collections. The dynamic nature of the examination allows the diagnosis of functional pathological conditions and is also used to guide aspiration and lavage. Assessment of superficial lumps and masses can be performed as a first line before triaging to other modalities such as MRI. It is also used for vascular assessment and the diagnosis of DVT.
•Intracavitary transducers: these place the transducer as close as possible to the area of interest. They include transvaginal, transrectal, urethral, oesophageal, and intravascular probes. They are usually high-frequency transducers that produce detailed high-resolution images. Transvaginal USS is more invasive than transabdominal scanning but is used in the routine assessment of gynaecological disorders. It can also be used for infertility monitoring, egg retrieval, and the exclusion of suspected ectopic pregnancy. Transrectal scanning is used for screening, assessment, and biopsy of suspected prostatic pathology, as well as rectal pathology including staging rectal cancers. Endo-anal probes may be used to assess morphology and characterize tears of the anal sphincter.
•Contrast agents: US contrast agents are available as an additional tool in diagnosis, although currently used primarily in academic centres. These are micro-bubbles, which are stable over a period of time, and may be used to improve anatomical detail, assess tubal patency (hysterosalpingography), assess tumour vascularity, and characterize focal masses (e.g. within the liver), and for contrast enhancement.
Fig. 13.28 Trans-axial view of the gall bladder on US demonstrating a soft tissue mass in the lumen, suspicious for carcinoma. There is cholelithiasis, a common coexistent entity. The arrow shows an abnormal interface with the liver parenchyma, suggestive of local infiltration.
Fig. 13.29 Colour Doppler image in the same patient showing abnormal vascularity in the wall of the gall bladder ( Colour plate 5.)
US is the 1° imaging modality in obstetric imaging, with MRI being used for problem-solving. USS is performed via both the transabdominal and transvaginal approach. Imaging is never performed in isolation and should always be performed in conjunction with clinical information, such as the patient’s menstrual status (including date of last menstrual period), presence/absence of pain and vaginal bleeding, as well as knowledge of biochemical parameters including serum β-hCG when available.
•Confirm an intrauterine pregnancy (IUP).
•Confirm the presence of a gestational sac and date the pregnancy.
•Determine the fetal number and placentation.
•If there is bleeding, assess the viability of pregnancy (possible aetiologies in this scenario include a normal IUP, impending abortion (missed, incomplete, or impending), ectopic pregnancy, or a subchorionic bleed).
•8- to 12-week gestational age dating US (most accurate form of pregnancy dating).
•Measurement of crown–rump length (margin of error ± 5 days).
•Change the estimated date of confinement (EDC) to US date if >5 days discrepancy from EDC based on last menstrual period.
•11- to 14-week gestational age nuchal translucency US (assess fluid behind the fetal neck); early screen for trisomy 21.
•Determine the fetal number and viability.
•Locate and assess placental morphology.
•Estimate the volume of placental fluid.
•Assess gestational age and evaluate growth (margin of error ± 10 days).
•Assess the cervix and look at adnexae.
•Fetal presentation (cephalic, breech).
•Biophysical profile and serial growth.
Typically performed at 15–16 weeks with US guidance. Indications include advanced maternal age, abnormal biochemical markers (triple screen or AFP), and a history of genetic/chromosomal disorders. CVS typically performed earlier (10–12 weeks) and also under imaging guidance using the transabdominal or transcervical approach.
•Gestational sac: the product of implantation and is usually visible within the uterus at 2–3mm.
•Normal mean sac diameter (MSD, mm) + 30 = days of pregnancy.
•Normal landmarks (transvaginal scan) (see Table 13.9).
•MSD >8mm: yolk sac should be visible.
•MSD >16mm: heartbeat should be present (crown–rump length >5mm).
•Other criteria worrisome for abnormal pregnancy:
•Crown–rump length of <7mm and no heartbeat.
•Mean sac length of 16–24mm and no embryo.
•Absence of embryo ≥6 week after last menstrual period.
•Small gestational sac also has a high risk of subsequent pregnancy loss (>90%). MSD (mm) to crown–rump length (mm) <5mm indicates loss of pregnancy
•Empty sac: one without a yolk sac or embryo. May represent a very early IUP (if MSD <8mm) or an embryonic pregnancy (if MSD >8mm), or a pseudo-gestational sac as seen in ectopic pregnancy.
Table 13.9 Transvaginal scan landmarks (accuracy ± 0.5 week)
| Age | β-hCG | Gestational sac | Yolk sac | Heartbeat | Embryo (fetal pole) |
| 5 weeks | 500–1000 | + | − | − | − |
| 5.5 weeks | >3600 | + | + | − | − |
| 6 weeks | >5400 | + | + | + | − |
| >6 weeks | + | + | + | + |
A full review of obstetric imaging is beyond the scope of this chapter.
USS remains the modality of choice for initial assessment of pelvic pathology in ♀ and can be used to assess uterine morphology and endometrial thickness, to exclude focal uterine pathology such as leiomyomas (fibroids), and for initial assessment of adnexal pathology.
Normal endometrium is echogenic with a surrounding hypo-echoic halo. Thickness is variable, depending on the stage of the menstrual cycle and the patient’s menstrual status (e.g. pre- or post-menopausal). Typical values range from <4mm in the menstrual phase, 4–8mm in the proliferative phase (up to day 14 of the cycle) to 7–14mm in the secretory phase.
The post-menopausal uterus is typically atrophic and may be modified by the administration of exogenous hormones (hormone replacement therapy (HRT)), which will also influence endometrial thickness. Normal thickness <5mm if no HRT usage.
•Indications: for assessment of infertility, to define uterine anatomy, and to evaluate tubal patency as a precursor for in vitro fertilization or for evaluation of congenital anomalies.
•Procedure performed at days 6–12 of menstrual cycle. Foley catheter inserted into the cervical canal, and contrast hand-injected to define the above. Complications include pain and infection. Contraindications are active infection, pregnancy, or recent uterine surgery.
Include locating and confirming the presence of leiomyomas (often pre- and post-uterine fibroid embolization (UFE); Interventional radiology, pp. 844–847), confirming the presence of adenomyosis, endometriosis, in the assessment of congenital uterine anomalies, as well for the assessment of complex pelvic or adnexal masses.
T2W imaging of the uterus defines the zonal anatomy and is invaluable in staging neoplasms. MRI is the modality of choice for tissue characterization and in this setting will demonstrate small quantities of blood products (as in endometriosis plaque), as well as showing tissue content such as intra-lesional fat (dermoids).
This technique differs from conventional radiography in that it is able to visualize a vast spectrum of absorption values, and therefore tissue densities. Furthermore, being a tomographic technique, the resultant image is essentially 2D and overcomes the problem of confusing overlap of 3D structures on plain film. The image is a grey-scale representation of the density of tissues (attenuation), as depicted by X-rays. Each image is made up of a matrix of squares (pixels), which collectively represent the attenuation values of tissues within that volume (voxel). With conventional CT, separate exposures are made for each slice. Current scanners can acquire data in a continuous helical or spiral fashion, shortening the acquisition time and reducing artefacts caused by patient movement. This improves the overall throughput and ↑ the likelihood of a diagnostic scan, particularly in unco-operative patients. The volumetric data that are acquired may be manipulated by image processing and displayed in a variety of techniques, including 3D reformats and ‘virtual’ endoscopy.
The attenuation values are expressed on an arbitrary scale (Hounsfield units), with water being 0, air being −1000 units, and bone +1000 units. The range of densities displayed on a particular image can be manipulated by altering the window width and level. This also allows discrimination of tissues that differ in density by as little as 1%.
Prior to scanning the abdomen or pelvis, dilute oral contrast is given to opacify the bowel. IV contrast is given to aid the problem-solving process and differentiate vascular-enhancing lesions from surrounding tissue.
Multislice CT scanners are third-generation scanners with helical capabilities and low-voltage slip rings, which acquire anywhere between 64 and 320 slices (and counting!) per X-ray tube rotation.
Dose management has become more of a concern with the ↑ utility of CT across a spectrum of pathologies. The dose is dependent on a number of patient- and scan-related variables, including patient habitus, the volume (area) scanned, the number(s) of acquisitions, as well as the desired resolution and image quality.
To address this problem, there have been innovations in reconstruction to minimize the dose without impacting on noise and including instances where data are incomplete. These include adaptive statistical iterative reconstruction. There is minimal, if little, impact on spatial or contrast resolution.
There are a wide variety as detailed below. CT is often the most diagnostic cross-sectional examination and more definitive than USS in many instances.
Due to the relatively high radiation dose, CT should be avoided in pregnancy. Artefact from indwelling, high-density foreign material, e.g. hip prosthesis, dental amalgam, and barium, may limit the diagnostic quality of the examination. Claustrophobia is less of a problem, compared to MRI.
•CNS/spine: CT remains the tool for 1° diagnosis, pre-surgical assessment, treatment monitoring, and detection of relapse in many CNS disease conditions. MRI is superior in the posterior fossa and parasellar region and for assessment in MS, epilepsy, and tumours. Where MRI is not available, it is useful for assessment of degenerative spinal and disc disease. It is superior to MRI in the assessment of head injury. In the context of trauma, MRI is only utilized when CT is −ve despite strong clinical suspicion. CT is also used as the 1° modality in the evaluation of acute stroke and in the emergency settling prior to LP of patients suspected of CNS infection such as meningitis.
•Orthopaedics/trauma: uses include diagnosis and staging of bony and soft tissue neoplasms and assessment of vertebral, pelvic, and complex extremity trauma (e.g. tibial plateau fractures). It is also used in the detection of loose bodies, in the assessment of acetabular dysplasia, and in providing an answer in joint instability (especially in shoulders, wrists, and elbows where it may be performed as an adjunct to/in conjunction with conventional arthrography).
•Oncology/radiotherapy: staging of solid tumours, treatment planning, and the detection of relapse. CT is of particular value in obtaining whole body scans in oncology due to the speed and ease of use with the advent of multislice CT. CT is used for radiotherapy treatment planning to allow more precise targeting of treatment.
•Chest: indications include the staging of bronchogenic carcinomas, characterization of solitary nodules, diffuse infiltrative lung disease, widened mediastinum/mediastinal masses, and pleural abnormalities. With multislice CT, pulmonary angiography has advanced the diagnosis of Pes, particularly when V/Q scanning is indeterminate or equivocal. Helical CT is equivalent to formal angiography in the detection of emboli within proximal arteries of < fifth/sixth generation. Sensitivity (80–100%, specificity 78–100%).
•Abdomen: applications include the diagnosis of abdominal pathology, which may be of traumatic, neoplastic, inflammatory, or infective origin (see Figs 13.31–13.34). CT is particularly useful for masses, pancreatic and hepatic disease, detection of the site and nature of obstructive jaundice, and the assessment of abdominal trauma. It is also used in the pre-surgical assessment of abdominal aneurysms (see Fig. 13.35) and as an aid to interventional techniques ( Interventional radiology, pp. 844–847).
Fig. 13.31 Direct coronal reformat through the liver showing findings consistent with 1° sclerosing cholangitis. Note the markedly thickened bile duct wall (arrows).
Fig. 13.32 Free intraperitoneal air 2° to perforation of a gastric ulcer. Note the thickened antrum of the stomach.
Fig. 13.33 Virtual barium enema image reconstructed from CT colonoscopy. The arrow shows the location of the polyps.
Fig. 13.34 Reformatted maximum intensity projection MIP image of an abdominal CT showing small bowel obstruction due to the presence of a caecal carcinoma (arrows).
Fig. 13.35 Reformat of a CT angiogram to assess the extent of RAS in this patient who has bilateral common iliac stents.
This is a non-invasive technique, which displays the internal structure, whilst avoiding the use of ionizing radiation. The nuclei of certain elements align with the magnetic force when placed in a strong magnetic field. These are usually hydrogen nuclei in water and lipid (at clinical field strengths), which resonate to produce a signal when a radiofrequency pulse is applied. When the radiofrequency pulse is switched off, the protons return to their pre-excitation axis, giving off the energy they absorbed. The energy can be measured with a detector and used by a computer to display anatomical information. The T1 and T2 signal characteristics of common tissue types are seen opposite (see Table 13.10). Further discussion of the physics is beyond the scope of this chapter. Inherent tissue T1 and T2 characteristics depend on the longitudinal relaxation (T1) and transverse relaxation (T2) times of the protons in that tissue. Pathologic processes alter the relaxation times of the tissue and will produces signal abnormalities.
MR image weighting (e.g. T1W or T2W images) depends on the repetition time (TR) and echo time (TE) used to obtain images.
•Contrast is due to inherent T1 relaxation.
•Provides good anatomical information.
•Fat is displayed as high signal (white).
•Distinction between cystic (black) and solid structures is possible.
•Good evaluation of marrow signal.
•The sequence of choice when evaluating enhancement, as gadolinium administration makes structures of even higher signal intensity on T1W images (see Tables 13.10 and 13.11).
Table 13.10 Examples of sequences used in clinical practice
•Technique of choice for evaluating pathology.
•Fluid is of high signal and therefore optimally displays oedema.
•Improved soft tissue contrast allows evaluation of zonal anatomy of organs such as the uterus and prostate.
Table 13.11 MR signal intensity of common tissues
| Tissue or body fluid | T1 signal | T2 signal |
| Air | Nil | Nil |
| Bone or calculi | Nil | Nil |
| Fat | High (bright) | Medium to high |
| Proteinaceous fluid (e.g. abscess or complex cyst) | Medium | High |
| Muscle | Low | Low to medium |
| CSF, urine, bile, or oedema | Low | High |
| Blood (depends on age), hyperacute (oxyHb), chronic (haemosiderin) | Low/low | High/low |
MRI principles are used to exploit the properties of flowing blood. Images generated display structures containing flowing blood, with suppression of all other structures. These principles can be further modified, so that only vessels with flow in a specific direction (i.e. arteries vs veins are) visualized. MRA is currently being used in the evaluation of suspected cerebrovascular disease, renovascular disease, and peripheral vascular disease.
MRI techniques have evolved, such that diffusion imaging utilizes the diffusion of water protons in the diagnosis of evolving ischaemia. This technique shows how movement of water molecules is impeded by cytotoxic oedema of ischaemic cells. These are manifested by signal changes that show early evidence of cerebral ischaemia prior to structural changes becoming apparent.
Diffusion MRI comprises two separate components—DWI and apparent diffusion coefficient (ADC) which are interpreted together to evaluate the diffusion characteristics of tissue. DWI has had a profound impact in the assessment of cerebral infarcts and is ~95% sensitive and specific for infarcts within minutes of onset of symptoms. The ADC map shows pure diffusion information without any T2 weighting. Reduction in diffusion is therefore of low signal (hypointense) on the ADC map. The b-value is an important concept for impacting sensitivity for the detection of diffusion abnormalities. The higher the b-value, the more contrast the image provides for detection of reduced diffusion. DWI is also increasingly used in the oncological setting both at the time of staging but also for evaluation of treatment response.
Similarly, early ischaemia of the myocardium is detectable on MRI. This has great therapeutic potential, as early treatment may prevent the establishment of ischaemia and result in overall improvement of ventricular function and survival. MRA is also being used to depict coronary vessel disease non-invasively.
An advanced technique where the brain is repeatedly imaged as a bolus of gadolinium (contrast) is injected. Gadolinium causes a magnetic field disturbance which results in a transient reduction in image intensity. As these are echo-planar T2*images, they can be acquired quickly and are invaluable in imaging of strokes and tumours. The signal changes associated with gadolinium can be plotted over time for a selected brain volume. The time signal plots can be manipulated to obtain parameters related to cerebral perfusion.
The indications are legion and continue to grow. There are a wide variety of indications, summarized below ( Applications, pp. 830–832). MR is especially useful in imaging the brain, spine, peripheral limbs, and joints, neck, and pelvis. Again, improvements in scanner hardware and software have had huge impact on clinical practice. The prior limitations of long scan times have been overcome by robust sequences that can be performed in a breath-hold. This means that respiratory and peristaltic artefacts are no longer an issue when imaging in the chest and abdomen.
These largely apply to patients with magnetically susceptible devices or materials whose movement or loss of function can have deleterious consequences. These include cardiac pacemakers, metallic fragments, and prosthetic heart valves. Relative contraindications include pregnancy (especially the first trimester) and claustrophobia. MRI magnets are relatively confined and even those who are not normally claustrophobic may be provoked.
•The spine: MR imaging is superior to other techniques in displaying anatomy and is the technique of choice in assessing disc disease and the post-operative back, in evaluating neural compression (benign or malignant), in imaging acute myelitis and infection (such as discitis or osteomyelitis), and in excluding marrow infiltration. Contrast is helpful in assessing the post-operative back to distinguish scar from residual herniation, as well as for confirming extruded fragments. It also helps confirm the presence of neuritis 2° to a disc herniation.
•CNS: imaging of the CNS is used to evaluate mass lesions, hydrocephalus, white matter disease, leptomeningeal pathology, cerebrovascular disease (see Figs 13.36, 13.37, 13.38,), degenerative disorders, and visual and endocrine disorders such as pituitary dysfunction. In trauma/acute haemorrhage, CT is the preferred technique ( Neuroradiology, pp. 856–859).
•Paediatric: the uses here include assessment of perinatal trauma/anoxic injury, congenital anomalies, and developmental delay. Within the spine, it is invaluable in the assessment of spinal dysraphism and progressive scoliosis.
•Musculoskeletal: along with CNS disease, this is a major component of the MRI workload. It has revolutionized musculoskeletal imaging and is used to characterize meniscal pathology, ligamentous injury, and degeneration and sequelae of trauma in the knee, shoulder, wrist, and ankle. Further uses include imaging mass lesions, assessing the extent of infection, and diagnosing early avascular necrosis (AVN).
•Chest/cardiac: within the thorax, MRI is useful for assessment of apical lesions such as Pancoast’s tumours (see Fig. 13.39), chest wall and brachial plexus lesions, and mediastinal masses. Cardiac applications are legion and fast-evolving; they include imaging of the great vessels to exclude congenital/acquired aortic disease (including dissection) and the diagnosis of PE.
•Abdominal/pelvic MRI: within the abdomen, MR is often a problem-solving tool and can be used to more confidently characterize focal liver and pancreatic lesions, as well as assess diffuse liver disease. It is also of use in evaluating indeterminate adrenal masses. Within the pelvis, uses include imaging of congenital anomalies, as well as staging tumours such as cervical (see Figs 13.40 and 13.41), prostate, and rectal tumours. There have been rapid advances in techniques for imaging bowel-related pathology.
•Interventional MRI: open MRI units image patients in large-bore or C-shaped units, rather than the closed narrow tunnel used in conventional units. They can therefore be used for claustrophobic patients and to provide imaging guidance for interventional procedures. Disadvantages include a low magnetic field strength (0.1–0.3T vs 1.5T) and a limited anatomical and spatial resolution due to their basic construct.
Recently, short-bore magnets have been developed that combine the accuracy of a tunnel scanner and the comfort of an open MRI scan. Although they are not completely open, they are much less constrictive because of the short-bore magnet (shorter tunnels) but can produce a high field.
Fig. 13.37 Coronal reformatted MRI image showing a tight stenosis of the distal vertebral artery on the right.
Fig. 13.38 AP coronal MRA showing mild irregularity of the carotid siphon on the left. The images are examined in multiple projections to exclude anomalies such as stenosis or small aneurysms.
Fig. 13.39 Sagittal T2W MRI image in patient with a superior sulcus (Pancoast’s) tumour showing invasion into the chest wall.
Fig. 13.40 Axial T2W sequence showing bilateral parametrial infiltration in this patient with a cervical mass.
Fig. 13.41 Sagittal and axial T2W images showing a large cervical carcinoma. MRI is the modality of choice for local staging.
•Obtain two films at right angles to one another (most commonly an AP and a lateral to rule out a fracture).
•Image proximal and distal joints.
•Bone scanning is more sensitive, but less specific, than plain films to rule out a fracture. (Not useful in the acute setting.)
•CT is invaluable for complex injuries (e.g. spine, calcaneus, and sacrum).
•MRI is used to assess ligaments, tendons, joint capsules, menisci, and cartilage.
•Site of fracture: assess if proximal/distal and intra- vs extra-articular.
•Type of fracture: simple (transverse, oblique, spiral) vs comminuted.
•Degree of displacement: usually described with reference to the distal fragment.
•Soft tissue involvement: exclude foreign bodies, presence of gas. Open (compound) vs closed.
•Trauma: obtain a cross-table lateral first (this has the highest yield), and then perform the remainder of the cervical spine series (AP and open mouth peg views), if patient mobility allows and a high index of suspicion. All seven cervical vertebral bodies should be visualized (a large number of cervicothoracic injuries are missed because of inadequate views). If not seen, request a specialized lateral view (swimmer’s) or a CT. Then sequentially evaluate:
•Alignment: assess the following lines shown in Fig. 13.42. They should be parallel with no step-offs.
•Bones: inspect C1 and C2. The anterior arch of C1 should be 3mm from the dens in adults (5mm in children). The vertebral bodies should be intact, and they should be uniform in size and shape. Check disc spaces for any inordinate narrowing or widening which may be post-traumatic.
•Soft tissues: look for abnormal widening or a localized bulge; 50% of patients with a bony injury will have soft tissue thickening. The soft tissues should be no more than one-third of a vertebral body until C4, and a vertebral body width thereafter.
•The peg views: do not mistake a superimposed arch of C1 or the incisors as a fracture. Important points to remember are:
•The lateral margins of C1 and C2 should align.
•The spaces on either side of the peg should be equal (see Fig. 13.42).
In the routine setting, cervical spine films are taken to exclude spondylosis (disc space narrowing and osteophytes) and atlantoaxial subluxation, which results in long tract signs and cord compression (RhA, ankylosing spondylitis, Down’s syndrome). (See Fig. 13.43 for image showing a large osteophyte.)
Fig. 13.42 Schematic diagram depicting the lines that need to be assessed when looking at a lateral film of the cervical spine.
Degenerative disease is common with disc space narrowing, end-plate sclerosis, and osteophyte formation. Wedge compression fractures are common in the osteoporotic spine and need to be distinguished from the more sinister causes (absence of paraspinal mass, posterior elements spared). Multiple collapsed vertebrae are found in osteoporosis, neoplastic disease, trauma, and histiocytosis X. Bone density may help narrow the differential, which includes ↑ (sclerotic metastases, lymphoma) and ↓ (acute infection, osteoporosis).
Spondylolisthesis is the subluxation of one vertebral body on another and may be degenerative or due to bilateral pars defects (spondylosis). This is a fracture/defect of the posterior elements of the vertebrae. In an oblique view, the posterior elements form a Scottie dog (with the pars making up the collar). This may be a purely incidental finding; however, if severe, it can result in neuroforaminal stenosis. Plain films are insensitive in the evaluation of disc disease. MRI is the investigation of choice for disc disease and its neurological complications.
Fractures typically occur at the thoracolumbar junction (90% at T11–L4). CT typically indicated other than in stable compression fractures, isolated spinous or transverse process fractures, and spondylolysis.
Plain film findings include paraspinal haematoma and widened interpedicular distance. An unstable injury may be accompanied by disruption of the posterior elements and widened interlaminar space, and is seen in the context of all fracture dislocations or if there is a compression fracture of >50%.
Pelvic fractures are complex, and there are many classification systems around. The pelvis should be regarded as being made up of three bony rings. The sacroiliac joints and the pubic symphysis are part of the main bony ring. A fracture of one ring is frequently associated with a second ring fracture (see Fig. 13.44).
•Sacroiliac joints should be equal in width.
•The superior surfaces of the pubic rami should align. The joint width should be no more than 5mm.
•The sacral foramina should form a smooth arc.
•Acetabular fractures are subtle—look for symmetry.
Stable fractures (single break of the pelvic ring or peripheral fractures) commoner. These include avulsion injuries (e.g. anterior superior iliac spine (ASIS), pubis, and ischial tuberosity), as well as sacral fractures and those of the ischiopubic rami.
Unstable fractures (pelvic ring interrupted in two places)—less common. All require CT for clarification of the extent of injury, as a plain film may underestimate the extent of posterior ring disruption (includes Malgaigne and bucket handle fractures).
•Bone texture: the pelvis is a common site for metastatic involvement, especially with urological malignancies, e.g. prostate (sclerotic metastases) and myeloma (multiple lytic lesions). Paget’s disease of the pelvis may mimic sclerotic metastases but tends to be confined to one hemipelvis and may expand or thicken bone.
•Sacroiliitis: sacroiliac joint involvement is common in seronegative arthropathies and is usually symmetrical in conditions such as IBD, ankylosing spondylitis, and hyperparathyroidism. More asymmetrical change is seen in Reiter’s disease and RhA. It is characterized by initial erosion and widening of the joint, resulting in chronic sclerosis, which has a preferential involvement of the lower one-third of the joint (iliac > sacral side).
•AVN of the femoral heads: an important finding but is often advanced when plain film findings are seen. Radiographically occult AVN may be detected on MRI or a bone scan. On plain X-ray, it is characterized by sclerosis, flattening, and fragmentation of the femoral head. Subchondral crescents are pathognomonic. AVN can also be a sequel of trauma, but bilateral AVN is seen in conjunction with steroid therapy, sickle-cell disease, and as part of Perthe’s disease.
Fig. 13.44 The pelvis is made up of bony rings: the main pelvic ring and two smaller rings made up of the pubic and ischial bones.
Angiography is catheterization of a vessel followed by subsequent opacification with a water-soluble iodine-containing contrast medium. Catheterization is usually performed using the Seldinger technique.
•What: is the type of study—angiogram, digital subtraction angiogram (DSA), venogram?
•Where is the catheter and which vessel? Is it a large vessel or a selective/super-selective angiogram?
•When: what phase is it (early/late arterial, parenchymal, or venous)?
•Vessels: is there contrast in unexpected vessels (extravasation or neovascularity)? Is the vascular contour normal (look for irregularity, stenosis, dissection, or encasement)?
•Intervention (previously placed stents, filters, coils, clips, or drains).
Catheters are sized in French (Fr) where 1 Fr = 0.33mm. Sheath vs catheter. A sheath has a defined luminal diameter; however, the overall diameter will generally be larger.
High-flow (flush) catheters have multiple side holes and are used for large vessel angiography.
Selective catheters have a single hole at the end. The distal portion has numerous shapes tailored to a specific or general purpose.
•Demonstration of arterial anatomy prior to surgery where this is likely to influence surgical management.
•To elucidate the nature of arterial disease, e.g. occlusions, stenoses, thrombi, aneurysms, and vascular malformations in coronary, carotid, and cerebrovascular disease. Also in the setting of endovascular procedures (aneurysm repair, thrombolysis, stenting, and angioplasty).
•To identify the source of bleeding in the GIT or following trauma.
•To demonstrate tumour circulation (often prior to embolization).
•Due to advances in technique, non-invasive assessment of vessels by techniques such as colour Doppler US, CT angiography, and MRA is often used as first line.
Puncture site haematoma, infection, pseudo-aneurysm, AV fistula, dissection, thrombosis, embolic occlusion of a distal vessel.
Volumes used are variable, depending on the area being imaged. The contrast agents are iodinated, non-ionic, and of low osmolarity, resulting in reduced toxicity. Nevertheless, potential side effects include anaphylaxis, hypotension, urticaria, and bronchospasm. Patients particularly at risk include those with a history of a previous reaction, iodine allergy, and atopy. Nephrotoxicity is a potential risk and may be exacerbated by dehydration. Contrast reactions are seen in 1/1000 patients. Risk of anaphylaxis is 1/400,000. Pre-medication with corticosteroids may reduce the incidence of reactions if contrast administration is essential, but this is not universally accepted.
These include pulmonary angiography (gold standard for detection of PEs), which is highly invasive, and therefore reserved for when thrombolysis or embolectomy are being considered. Cerebral angiography is useful in the diagnosis of aneurysms, AVMs, tumour vascularity, and both intra- and extracranial vascular disease. Renal angiography is selectively performed to diagnose RAS and prior to embolization of tumours.
•DSA: a technique whereby there is subtraction of the contrast-containing shadows from the initial plain films (mask), resulting in an image containing opacified structures only. The resulting images may be digitized and manipulated. The overall advantage is smaller doses of contrast and smaller catheters may be used.
•Angioplasty: percutaneous transluminal angioplasty (PTA) is a method used to fracture the vascular intima and stretch the media of a vessel by a balloon. Atherosclerotic plaques are very firm and are fractured by PTA. Healing occurs by intimal hyperplasia. Indications include claudication or rest pain. A common alternate to surgical bypass, with 5-year patency similar to that of surgery.
•Intravascular stents: typically, metallic stents used when there has been unsuccessful PTA or in cases of recurrent stenosis, venous obstruction/thrombosis or as transjugular intra-hepatic portosystemic shunt (TIPS) shunts ( Interventional radiology, Transjugular intrahepatic portosystemic shunt, p. 846). They can either be balloon-expandable or self-expandable. Aortic stent grafts used to treat aortic aneurysms or dissections are typically a combination of a metallic stent with synthetic graft material. Stents can also be used in revascularization procedures when there is long segment stenosis, total occlusion, or ineffective PTA.
•Used to selectively occlude vessels by introducing a variety of materials via a catheter. Permanent materials used include metallic coil, balloons, and cyanoacrylate glue. Temporary embolic materials include gel foam and autologous blood clots. This technique is used at active bleeding sites and to reduce tumour vascularity preoperatively in resectable tumours. It can also be used to treat AVMs, for symptomatic uterine fibroid embolization ( Figs 13.49 and 13.50, p. 848), and in varicocele embolization for infertility. Proximal occlusion of a vessel is equivalent to surgical ligation and does not compromise collateral flow.
•Distal embolization usually infarcts tissue and is followed by necrosis.
•Complications include post-embolization syndrome (fever, pain, elevated WBC), infection of embolized area, and reflux of embolic material (non-target embolization).
•Vascular catheterization: is also used to selectively infuse vessels, as with thrombolytic treatment or rarely with cytotoxics. Vascular stenting is of ↑ use in coronary and peripheral vascular disease. IVC filters (see Fig. 13.45) are metallic umbrellas used to mechanically trap emboli and prevent venous thromboembolic disease. They are percutaneously placed via the femoral, jugular, or antecubital vein. In the treatment of patients with recurrent PEs despite anticoagulation or where anticoagulation is contraindicated. IVC filters can be temporary (retrievable) or permanent. They are placed infrarenally to avoid renal vein thrombosis.
•Is the infusion of a fibrinolytic agent (urokinase, streptokinase, TNK, tissue plasminogen activator (tPA)) via a catheter inserted directly into a thrombus. This can restore blood flow in a vessel obstructed with a thrombus or embolus.
•Indications include treatment of an ischaemic limb, early treatment of MI or stroke to reduce end-organ damage, and treatment of venous thrombosis (DVT) of the leg or PE.
•Contraindications include active bleeding, recent intracranial event (CVA, tumour, or recent surgery), non-viable limb, and infected thrombus.
Central venous access: there are a variety of devices available—peripherally inserted central catheters (PICCs), external tunnelled catheter (Hickman), subcutaneous port (Portacath™). Indications include chemotherapy, total parenteral nutrition (TPN), long-term antibiotics, administration of fluids and blood products, and blood sampling. Potential complications are venous thrombosis, infection, and pneumothorax.
Interventional radiology is a sub-speciality where a variety of imaging modalities are used to guide percutaneous procedures. This may obviate alternative surgical procedures and consequently result in lower morbidity. Interventional procedures are usually carried out under LAn or using conscious sedation ( Interventional radiology, Conscious sedation, p. 846), and on an outpatient basis, thereby considerably reducing bed occupancy. There is a huge range of procedures that are currently performed. The following is a limited list of some of them (see also Table 13.12).
Biopsy needle placement may be done under fluoroscopy, CT, MRI, and US. This provides a non-operative confirmation of tissue diagnosis and, in the case of a suspected malignancy, it is possible to accurately plan treatment. For histology, a 14–18G needle is used. With a fine-aspiration needle (20–22G), material may be obtained for cytology. Using imaging guidance, there is avoidance of damage to vital structures such as blood vessels, solid organs, and bowel loops. With chest biopsy, there is a 30% risk of pneumothorax. Other potential complications include false −ve samples (due to sampling error or tissue necrosis). Bleeding is more likely to occur in patients with underlying coagulopathies (vigorous pre-biopsy screening important for safety) and in patients with ascites.
With image guidance, surgical intervention may be avoided by accurate placement of a drainage catheter. Calibre varies from 8 to 14F, depending on the nature of the underlying fluid. Regular irrigation of the catheter may be necessary to ensure successful drainage. Successful resolution may be impeded in the more complex and multiloculated collections. There are a variety of routes of access other than the conventional percutaneous, including transvaginal, transrectal, and transgluteal. Potential complications include injury to overlying structures and sepsis.
Can be via double J stents, which are placed into an obstructed collecting system, with the distal catheter tip lying in the bladder. More short-term drainage is achieved via a percutaneous nephrostomy. Here, the obstructed kidney is punctured under fluoroscopic or US guidance, and a catheter placed in the renal calyx (preferably the lower pole). This is the technique of choice in the acutely obstructed or infected kidney. Nephrostomy insertion is also performed in the setting of ureteric injury either with or without accompanying peritonitis. Potential risks include septic shock, haematuria (due to pseudo-aneurysm or AV fistula), or injury to regional structures.
Surgical outcome in patients with malignant bile duct obstruction is often poor. This may be due to carcinoma of the pancreas or cholangiocarcinoma. Biliary stenting alleviates obstruction and improves quality of life. Stenting may be performed at ERCP or percutaneously via antegrade puncture through the liver (PTC to delineate the anatomy, being performed first). Other than alleviating biliary obstruction, PTC can provide biliary diversion in the case of ductal injury (post-traumatic or post-surgical). Often there is unilateral obstruction which requires only treatment of the affected side. Hilar obstruction, however, due to a hilar (Klatskin) tumour requires two biliary drains.
Percutaneous drainage of the gall bladder (cholecystostomy) is indicated for the treatment of acute calculous or acalculous cholecystitis in patients who are not surgical candidates or as a temporizing measure prior to definitive surgery.
Other GI interventions include stenting/balloon dilatation of oesophageal strictures, stenting of obstructive colonic neoplasms (see Fig. 13.46), and percutaneous gastrostomy or gastrojejunostomy insertion. Oesophageal, head and neck, and neurologic disease may necessitate percutaneous gastrostomy. In some instances, it may be used for long-term bowel decompression, for instance in a prolonged ileus.
A procedure whereby a connection is made between the hepatic and portal veins to reduce portal pressure in patients with portal hypertension. The mortality is considerably lower than in acute shunt surgery, particularly in the context of an acute variceal bleed, which has failed to respond to sclerotherapy.
Form of sedation whereby the patient is given sedation and analgesic medication but remains conscious and easily arousable. At all times, the following are monitored—BP, pulse oximetry, ECG, and heart rate. Typical drugs used include a short-acting benzodiazepine (e.g. midazolam) and a narcotic analgesic (e.g. fentanyl), administered in small aliquots.
Table 13.12 Established and newer interventional applications
| Established techniques | Newer interventional applications |
| Arterial and venous sampling | AVM embolization |
| Biliary drainage, stenting, angioplasty, biopsy, and stone extraction | Chemoembolization |
| Diagnostic angiography | Cryoablation of liver tumours |
| Embolization | |
| Oesophageal dilatation | Endovascular repair of abdominal aortic aneurysms with stent grafts |
| Fallopian tube recanalization | Radiofrequency ablation of tumours |
| Feeding tube placement | Uterine artery embolization for symptomatic fibroids |
| IVC filter placement | Varicocele embolization |
| Nephrostomy placement | Vertebroplasty |
| Pain management (e.g. coeliac ganglion block, selective and non-selective nerve block) | |
| Percutaneous biopsy, cholecystostomy, and drainage of fluid collections | |
| 1° gastrostomy, gastrojejunostomy, or jejunostomy tube placement | |
| Thrombolysis | |
| TIPS insertion | |
| Ureteral stent placement | |
| Vascular angioplasty and stent placement | |
| Venous access and foreign body retrieval |
With stent grafts, this is a new image-guided, catheter-based approach that provides a valuable alternative to standard open surgical repair. Radiological imaging plays an essential role in pre-procedure evaluation, the procedure itself, and patient follow-up. The ultimate goal remains the same—complete exclusion of the aneurysm sac to prevent rupture. Advantages include lower blood loss, shorter ITU stay, and rapid recovery. Complications include graft thrombosis, kinking, pseudo-aneursym caused by graft infection, and endoleak. Bifurcation grafts are used mainly for abdominal aortic aneurysm (AAA) repair and aorto-iliac occlusive disease. Tube grafts are used mainly for AAA repair.
Not all patients with tumours are eligible for surgical intervention because of unfavourable location of the tumour, adverse clinical conditions, or advanced disease. In addition, the cost, morbidity, and mortality associated with surgical resection have led to the search for other forms of therapy. Newer, minimally invasive treatments include intra-arterial chemoembolization, injection of ethanol, and radiofrequency ablation. Among the thermal ablative procedures, radiofrequency ablation has evolved into an established technique for non-invasive management of tumours in patients where underlying medical co-morbidities or tumour burden preclude definitive surgery or as a bridge to further therapy. For this procedure, US, CT scanning (see Figs 13.47 and 13.48), or MRI is used by the radiologist to guide percutaneous placement of long, thin (usually <18G), insulated needles into the tumour. The distal end (1–3cm) of each needle is not insulated and emits radiowaves. Electrodes are attached to a generator, and the electrical energy is converted to heat that kills cells through coagulation necrosis. The radiologist can vary the amount of current used, thereby tightly controlling the treatment radius. The entire treatment session usually lasts 1h and can be performed in the outpatient setting. The procedure is typically performed with conscious sedation and LAn. Radiofrequency ablation has been used to treat a variety of tumours, but the commonest utility is for hepatocellular carcinoma, liver metastases, and renal tumours.
Fig. 13.47 Contrast-enhanced CT showing several high-attenuation metastases overlying the dome of the liver.
Fig. 13.49 Pre-uterine artery embolization (UFE). Selective catheterization shows the supply to a large left-sided fibroid.
Fig. 13.50 Post-embolization with polyvinyl alcohol (PVA) showing no flow in the previously demonstrated fibroid.
•In long bones, divide the shaft into thirds.
•Use anatomical landmarks for description.
•Simple fracture: no fragments. Describe the orientation of the fracture plane, e.g. transverse, spiral, and oblique.
•Comminuted fracture: >2 fragments: T-, V-, and Y-shaped patterns, butterfly fragments.
Defined in relation to distal fragments.
Other important descriptors include:
•Displacement (e.g. medial, lateral, anterior, posterior).
•Angulation (direction of fracture apex, e.g. valgus or varus).
•Rotation (internal vs external).
•Distraction (refers to degree of separation of fragments).
•Impaction: fracture fragments are compressed, resulting in shortened bone.
Adjacent joints: are they normal? Is there dislocation, subluxation, or any intra-articular extension of the fracture line?
•Soft tissue involvement (foreign body, gas, calcification).
•Type of fracture (stress vs pathological).
•Stress fractures are of two types:
•Insufficiency-related (if abnormal underlying architecture, as in osteoporosis).
•Fatigue: when abnormal stress is placed on normal bone (as in march injuries).
•Pathological fracture occurs when fracture occurs in the setting of underlying bone disease or discrete lesion.
•Intra-medullary rods: usually hollow, closed nails. Rotation and shortening of bone fragments is avoided by distal interlocking screws.
•Kirschner wires (K-wires): these are used to temporarily fixate or treat fractures, particularly with small fragments or paediatric metaphyseal fractures. These are drilled into cancellous bone and can be used to maintain rotational stability if >1 is used. The ends are typically folded over to avoid any soft tissue or other injury.
•Circlage wires can be used to contain bone fragments.
•Other hardware includes staples, plates, nails, and screws.
•Polyethylene is a radiolucent substance used for joints with concave articular surfaces (e.g. the hip). Typically backed with metal as a support. Ultra-high molecular weight versions are also available.
•Silastic is also radiolucent and is used for hand and foot arthroplasty implants.
•Methylmethacrylate is used as a cement or can be directly injected into the medullary space. Radio-opaque.
Constrained prostheses are intrinsically stable and are therefore more likely to suffer loosening. Unconstrained prostheses rely on extra-articular structures to provide stability and are therefore less likely to dislocate.
A discussion of the types of prostheses is beyond the scope of this chapter. Potential complications of prostheses include, but are not limited to, the following.
•Polyethylene wear, dislocation, heterotopic bone formation, and infection can be seen. Small particle disease is seen as areas of osteolysis around the prosthesis due to macrophage-mediated reaction to particle debris. Cement leakage can cause necrosis and vascular and neurological injury, depending on location.
•Acute loosening occurs in the setting of infection. More chronic loosening is seen due to mechanical factors.
Critical role in evaluating disease extent, staging, and treatment planning. Lack of mobile protons, and an acellular matrix render cortical bone, ligament, tendon, and fibrous signal of low signal intensity on all sequences. Tissues like muscle, fat, osteoid, and chondroid matrix have differing signal intensities, which can be used to differentiate tumours. Marrow involvement can be excluded by T1W and STIR sequences ( Magnetic resonance imaging, pp. 828–832). The bone involved should be imaged in its entirety to exclude skip lesions. IV contrast is mandatory to assess lesional margin and tumour vascularity.
MRI is the mainstay in assessment of joint pathology and, in particular, is excellent in depiction of ligaments, cartilage, and joint effusions. It is therefore the modality of choice for infection, neoplasm, trauma, and arthritis. STIR shows marrow oedema, fluid collections, and bursal inflammation. Dual-echo steady state (DESS) is a sequence used for specific evaluation of articular cartilage. MRI is also the gold standard for marrow imaging. It is able to differentiate red from yellow marrow. T1W and STIR sequences are used for evaluating marrow pathology. Marrow oedema, as well as early involvement of the marrow by pathologies such as infection, neoplasia, and subtle trauma, is seen on STIR sequences when not easily evident on plain radiographs.
There are specific patterns that may be seen in the hand as an indicator of the underlying disorder. Some patterns are pathognomonic, whereas others are more non-specific.
•Generalized osteopenia: osteoporosis, multiple myeloma, and RhA.
•Coarsening of the trabecular pattern: common in haemoglobinopathies, especially thalassaemia and Gaucher’s disease.
•HPOA associations include carcinoma of the bronchus, IBD, and coeliac disease.
•Thyroid acropachy, commonest on the radial side of the thumbs.
•Juvenile chronic arthritis seen in about 25%.
•Carpal abnormalities: include short metacarpals (Turner’s syndrome, pseudo- and pseudopseudohypoparathyroidism), carpal fusion (inflammatory arthritis, RhA and juvenile chronic arthritis, post-trauma), and look for syndactyly and polydactyly.
•Soft tissue changes: e.g. ↑ in soft tissue thickness/size seen in acromegaly, localized ↑ seen in gouty tophi, nodes as in OA, soft tissue calcification seen in CREST (calcinosis, Raynaud’s syndrome, oesophageal motility dysfunction, sclerodactyly, and telangiectasia), and scleroderma.
•Joint disease: the hand X-ray above all may help in sorting out the type of arthropathy and aid rheumatological management (see Fig. 13.51). The ABCS approach is invaluable (see Table 13.13).
Table 13.13 An ABCS approach to interpretation of the hand radiograph
Two views are essential for ensuring no subtle injuries are missed. On a P-A view, the spaces between the carpal bones and the carpometacarpal articulations should be roughly equal (1–2mm). If a dislocation is present, then there is obliteration/overlap. Common injuries include Bennett’s fracture and the first metacarpal base injury extending into the joint surface with dislocation at the carpometacarpal joint. Scaphoid fractures are the commonest (75–90%) of carpal injuries. Because of the blood supply, there is a potential risk of osteonecrosis of the proximal pole.
May be performed in isolation or in conjunction with subsequent cross-sectional imaging (CT or MRI) for the following indications:
•Ligamentous and tendinous tears.
Plain films are obtained prior to the procedure. All joint fluid that is aspirated is routinely sent for culture. The contrast flows away from the needle if the tip is intra-articular.
Single contrast studies are performed to exclude non-calcified loose bodies. Double contrast studies are performed in the setting of cartilaginous injury such as a labral tear.
•Contraindications: allergy to contrast media, concomitant infection.
•Complications: pain, infection, allergic reaction (to contrast), and vasovagal reaction.
When performing MR, the examination is performed with dilute gadolinium.
•Single or multi-focal? Multiple lesions can be seen in benign disease such as enchondromas, fibrous dysplasia, as well as malignant aetiologies such as myeloma, metastases, and lymphoma.
•What is the degree of aggressiveness (type of destruction, as well as reparative pattern)? Cortical penetration implies aggressive behavior, as does an ill-defined or wide zone of transition (area between the lesion and normal bone). Moth-eaten and permeative patterns are also in keeping with aggressive disease.
•Location (within bone). Central and cortical lesions are usually benign. 1° tumours occur at sites of rapid growth, for instance the distal femur. Metastases occur at sites of high vascularity such as the spine or iliac bone.
•Tissue characterization by matrix. Matrix refers to the intercellular substance produced by tumour cells (is done in conjunction with a cross-sectional modality such as CT). Osseous matrix is seen with osteogenic tumours, and chondrogenic tumours have a cartilaginous matrix.
•Age is a very helpful way of narrowing the differential. Over 40 years, metastases are much commoner than 1° bone tumours.
•Is there a periosteal reaction? More aggressive lesions are associated with typical patterns such as sunburst, Codman’s triangle, or an onion peel configuration
•Soft tissue mass: more typically seen with malignant lesions.
Fig. 13.51 Asymmetric oligoarthritis with dominant involvement of the DIP joints. The pencil-in-cup appearance is typical.
•CT is the initial study for evaluation of neuropathology due to its speed, availability, and lower cost.
•Excellent for evaluation of bony abnormality.
•Done both with and without IV contrast, depending on the clinical indication. The use of contrast delineates vascular structures and anomalies.
•Visualization of the posterior fossa is inferior to MRI.
•MRI is useful in assessing diffuse axonal injury and the sequelae of head injury.
•Soft tissues (look for thickening which may suggest haematoma or oedema): assess the ear and orbital contents.
•Bone (use bone window): check the calvarium, mandible, and C spine for fractures and lytic lesions. Assess sinuses and mastoid air cells for opacity that may suggest the presence of fluid, pus, blood, mass, or fracture. If there has been facial trauma, the integrity of facial bones/orbit best assessed on coronal view.
•Dura and subdural space: assess symmetry of thickness (early clue to presence of blood). Look for crescentic or lentiform density.
•Cortical parenchyma: poor differentiation between grey and white matter suggestive of infarction, tumour, oedema, infection, or contusion. Hyperdense areas may suggest enhancing lesions, intracerebral haematoma, or calcification. If central grey matter nuclei (globus pallidus, internal capsule) are not visible, suspect infarct, tumour, or infection.
•Ventricular system: assess the position for midline shift or compression. High density suggests ventricular or subdural bleed. Enlargement is suggestive of hydrocephalus. High density in the cisterns may suggest blood, pus, or tumour.
•Symmetry: asymmetry of the parenchyma suggests midline shift.
Rule out skull fracture, extradural haematoma (lentiform shape), subdural haematoma (crescentic shape), SAH (see Fig. 13.52), SOLs (see Fig. 13.53), hydrocephalus, and cerebral oedema. Look for target lesions (when contrast given): metastases, abscesses, and fungal infections.
Evaluation of vascular lesions, including atherosclerotic disease, aneurysms, vascular malformations, and arterial dissection. Supplements information obtained on CT/MRI regarding tumour vascularity.
Conventional DSA is the gold standard for the assessment of neck and intracranial vessels; however, it is an invasive technique requiring an arterial (femoral) puncture. There is also potential for vessel injury at the time of catheter manipulation (e.g. dissection, occlusion, or vasospasm). Used for guidance of interventional procedures such as embolization.
Imaging may be −ve in the first 6h. Thereafter, look for:
•Oedema (loss of grey–white differentiation, sulcal effacement, and mass effect). Cytotoxic oedema develops within 6h and is seen on MRI.
•Within 24h, there will be a low-density wedge-shaped area corresponding to the vascular territory and extending to the cortical surface. Vasogenic oedema within 12–24h seen on CT.
•If ischaemic stroke, may see a hyperdense (bright) artery representing an intravascular thrombus or embolus.
•Acute haemorrhage seen if there is haemorrhagic transformation (white = acute blood). Density on NECT is 80–100HU relative to normal brain (40–50HU). There may be surrounding oedema. Will not be hyperdense if low Hct (<8g/dL). Subacute haemorrhage (3–14 days) may be hyper-, hypo-, or isointense to brain. Chronic haemorrhage (>2 weeks) is hypodense.
•Hypertensive haemorrhage typically seen in the pons in 80%.
•Prognosis depends on size, brainstem location, and intraventricular extension.
•Advances in MR sequences have revolutionized stroke imaging. Diffusion sequences (DWI) and perfusion-weighted imaging (PWI) demonstrate acute infarction, even in the context of a −ve CT.
•T2W and fluid attenuation inversion recovery (FLAIR) images show oedema with high signal.
•DWI shows high signal suggestive of cytotoxic oedema.
•Gradient echo identifies acute haemorrhage, whereas fast FLAIR can show acute subarachnoid blood. Time-of-flight angiography can non-invasively assess underlying vessels. If the infarct is thought to be venous (e.g. peripheral or haemorrhagic), then phase contrast MRV can exclude sinus thrombosis.
In the case of strokes in the posterior circulation, thin sectional axial images can exclude thrombosis or dissection within the vertebral arteries.
CT is important in the early stages of stroke evaluation to facilitate thrombolytic therapy. Highly accurate in identification of proximal occlusions in the circle of Willis and therefore aids triage to facilitate thrombolysis. Non-contrast CT is initially performed, as haemorrhage is an absolute contraindication to thrombolytic therapy.
MRI is the modality of choice and is highly sensitive (>90%), but with low specificity (71–74%). There can therefore be overlap with other entities, such as ischaemia, and confluent disease may simulate neoplastic mass lesions. T2W MRI shows ovoid high signal lesions in a periventricular distribution. Conventional T2 may underestimate the plaque size and overall plaque burden; advanced MRI techniques, such as DTI and MR spectroscopy, can have greater utility. FLAIR sequences show lesions in a periventricular distribution by suppressing (CSF) signal. Active lesions show enhancement following gadolinium. The spinal cord should also be screened to exclude involvement by MS.
Assessing the degree of myelination is an important part of excluding structural pathology in paediatric neurological disorders. MRI is the modality of choice in brain tumours, congenital anomalies, and hypoxic–ischaemic disorders (hypoxic–ischaemic encephalopathy (HIE)). DWI is useful in acute HIE, whilst spectroscopy is critical in metabolic disorders.
Fig. 13.52 Non-contrast CT head showing extensive SAH in a patient with underlying cerebral aneurysm (not shown).
Fig. 13.53 Axial T2W MRI showing multiple high signal lesions in the deep white matter of the right frontal lobe in a patient with lung carcinoma. The anterior lesion is cystic. These are consistent with metastases. Note the surrounding oedema.
The main indication is for penetrating acute trauma, although SXRs are of limited use in the era of widespread CT availability. Occasionally, the SXR is obtained as part of a skeletal survey in the evaluation of metabolic bone disease and endocrine disorders, and in the assessment of metastatic disease. It is still used in the assessment of sinus disease and in the evaluation of the post-operative skull or for confirmation of hardware placement (see Fig. 13.54).
None, but if there is suspicion of underlying intracranial injury, plain films are unnecessary ( Fractures and associated findings, p. 861).
The bones of the skull vault have an inner and outer table of compact bone, with spongy diploe between the two. Sutures are visible, even after fusion, and should not be mistaken for fractures. Blood vessels may cause impressions, as can small lucencies in the inner table near the vertex caused by normal arachnoid granulations which can be mistaken for small lytic lesions.
SXRs are basic and widely available, and yet potentially yield the least information in the context of trauma. The presence or absence of a skull fracture does not correlate with the presence or extent of any intracranial injury. Up to 50% of films may be technically unsatisfactory due to factors such as poor patient co-operation. With the advent of CT, this is the technique of choice for evaluation in acute injury and neurological deficit. It allows a firm diagnosis to be made and excludes other alternate diagnoses.
Basic radiographs include a lateral projection (obtained with a horizontal beam) and a further tangential projection, depending on the site of injury.
•A linear fracture: well-defined margins, no branching, and no sclerosis (cf. vascular markings or sutures that have an undulating course and sclerotic margins).
•A depressed fracture: ↑ density due to overlapping bone; those that are depressed by >5mm may lacerate the dura or cause parenchymal injury, and therefore need elevation.
•A fluid level/pneumocephalus: implies an associated basal skull fracture or a dural tear.
Note: pineal displacement is an inconstant finding and is not a reliable method of assessing the presence of intracranial injury.
Look for intracranial calcification; then examine the pituitary fossa, review the bony density, and look for focal areas of lysis and sclerosis.
•Intracranial calcification: the majority is normal and of no clinical significance. However, it may be of pathological significance—causes include 1° tumours, such as meningiomas, craniopharyngiomas, AVMs, and tuberous sclerosis, and infections such as toxoplasmosis.
•Raised ICP: in practice, plain film changes are only seen if the condition is long-standing. These include sutural widening (diastasis) and erosion of the lamina dura of the pituitary fossa.
•Enlargement of the pituitary fossa (normal dimensions: height 6–11mm, length 9–16mm): expansion will result in a double floor, loss of the lamina dura, and elevation/destruction of the clinoid processes. The vast majority of the lesions will be pituitary adenomas; other causes include meningiomas and aneurysms.
•Bone lysis: may be diffuse as in metastasis or myeloma. Large areas of bone destruction are seen in histiocytosis X and in the active phase of Paget’s disease (osteoporosis circumscripta).
•Bone sclerosis: may be localized as in meningiomas, depressed skull fractures, or generalized as in Paget’s sclerotic metastases, myeloma, and fluorosis.
•Sutural widening: may be due to raised ICP, infiltration by malignancy (neuroblastoma or lymphoma), or defective ossification as in rickets.
For abbreviations, see Table 13.14. For a list of adverse reactions to contrast agents, see Table 13.15.
Table 13.14 Abbreviations used in radiology
| AP | Anteroposterior |
| AXR | Abdominal X-ray |
| CT | Computed tomography |
| CXR | Chest X-ray |
| IVU | Intravenous urogram |
| MRI | Magnetic resonance imaging |
| P-A | Posteroanterior |
| USS | Ultrasound scan |
| V/Q | Ventilation perfusion scan |
Table 13.15 Management of adverse reactions to intravascular contrast agents
Data sourced from Standards for intravascular contrast administration to adult patients. 3rd edition RCR October 2014.
The order of appearance is more important than the absolute age of appearance, which varies widely. Remember ‘CRITOE’ (see Table 13.16).
Table 13.16 Order of appearance of ossification centres of the elbow
| Approximate average age (years) | |
| Capitellum | 1 |
| Radial head | 3–6 |
| Internal (medial) epicondyle | 4 |
| Trochlea | 8 |
| Olecranon | 9 |
| External (lateral) epicondyle | 10 |
•Loss of fracture line: 2–3 weeks.
•Remodelling of bone: 12 months.
•Types of paediatric fractures: torus (buckle) fractures—buckled cortex only.
•Greenstick fracture: incomplete transverse fracture with intact periosteum on concave side (ruptured on side of convexity).
•Type I: epiphyseal slip separates it from the physis (5–6%). S = slip of physis.
•Type II: fracture line extends into the metaphysis (50–75%). A = above physis.
•Type III: the epiphysis is vertically split, i.e. the equivalent of an intra-articular fracture (8%). L = lower than physis.
•Type IV: fracture involves the metaphysis, epiphysis, and physis (8–12%). T = through physis.
•Type V: crush injury with vascular compromise, i.e. poor prognosis for growth (1%). R = rammed physis.
For issues regarding radiation safety: 
https://www.gov.uk/government/collections/national-radiological-protection-board-nrpb-report-series
For information relating to radiological issues, guidelines in clinical management, training, and publications: http://www.rcr.ac.uk
Incorporates guidelines for use of contrast media and practice guidelines, as well as information on technical standards (e.g. teleradiology): http://www.acr.org
Also includes an image library with peer-reviewed published images: http://goldminer.arrs.org/
Educational website offering radiology cases, differential diagnoses, etc.: Learningradiology.com
CT imaging/protocols: http://www.ctisus.com
1 Royal College of Radiologists. Making the best use of clinical radiology services, Version 7.0.2. London: Royal College of Radiologists, 2012.
