7. Nose & Cavitas Nasi

Nose: Nasal Skeleton

Fig. 7.1 Skeleton of the nasus externus

Left lateral view. The skeleton of the nose is composed of bone, cartilage, and connective tissue. Its upper portion is bony and frequently involved in midfacial fractures, whereas its lower, distal portion is cartilaginous and therefore more elastic and less susceptible to injury. The proximal lower portion of the nostrils (alae) is composed of connective tissue with small embedded pieces of cartilage. The processus lateralis cartilaginis septi nasi is a winglike lateral expansion of the pars cartilaginea of the septi nasi rather than a separate piece of cartilage.

Fig. 7.2 Nasal cartilage

Inferior view. Viewed from below, each of the cartilagines alares majores is seen to consist of a crus mediale and crus laterale. This view also displays the two nares, which open into the cavitates nasi. The right and left cavitates nasi are separated by the septum nasi, whose inferior cartilaginous portion is just visible in the diagram.

Fig. 7.3 Bones of the lateral wall of the right cavitas nasi

Left lateral view. The lateral wall of the right cavitas nasi is formed by seven bones: the maxilla, os nasale, os ethmoidale, concha nasalis inferior, os palatinum, os lacrimale, and os sphenoidale. Of the conchae nasi, only the inferior is a separate bone; the conchae media and superior are parts of the os ethmoidale.

Fig. 7.4 Bones of the septum nasi

Parasagittal section. The Septum nasi is formed by six bones. The os ethmoidale and vomer are the major components of the septum. The os sphenoidale, os palatinum, maxilla, and os nasale (roof of the septum) contribute only small bony projections to the septum nasi.

Fig. 7.5 Lateral wall of the right cavitas nasi

Medial view. Air enters the cavitas nasalis ossea through the anterior nasal aperture and travels through the three nasal passages: the meatus nasi superior, meatus nasi medius, and meatus nasi inferior, which are the spaces inferolateral to the conchae superior, media, and inferior, respectively. Air leaves the nose through the choanae (posterior nasal apertures), entering the pars nasalis pharyngis.

Fig. 7.6 Septum nasi

Parasagittal section viewed from the left. The left lateral wall of the cavitas nasi has been removed with the adjacent bones. The septum nasi consists of an anterior cartilago septi nasi and a posterior bony part composed of several bones. The processus posterior cartilaginis septi nasi extends deep into the bony septum. Deviations of the septum nasi are common and may involve the cartilaginous part of the septum, the bony part, or both. Cases in which the septal deviation is sufficient to cause obstruction of nasal breathing can be surgically corrected.

Overview of the Cavitas Nasi & Sinus Paranasales

Fig. 7.7 Overview of the nose and sinus paranasales

A Coronal section through cavitas nasi, anterior view. B Transverse section, inferior view.

The cavitates nasi and sinus paranasales are arranged in pairs. The left and right cavitates nasi are separated by the septum nasi and have an approximately triangular shape. Below the base of the triangle is the cavitas oris. Note the relations of the nervus infraorbitalis and maxillary dentition to the sinus maxillaris.

The close proximity of the roots of the maxillary teeth (canine to second molar) to the sinus maxillaris (antrum) is very significant in clinical dentistry. Sinus pathology, for example, acute maxillary sinusitis due to an upper respiratory infection (URTI), can often be confused as dental pain originating from these teeth. Diagnosis is made by exclusion of dental pathology and observation of URTI symptoms, such as nasal discharge and stuffiness. Furthermore, the pain of acute maxillary sinusitis is often worsened by bending the head forward. There would also be tenderness on palpation of the cheeks.

The close proximity is also significant because the roots or the entire tooth can be displaced into the sinus maxillaris during extractions, requiring surgical removal (see Fig. 7.17).

Extracted upper molars may also cause an oro-antral fistula, an abnormal communication between the cavitas oris and the sinus maxillaris. Post-extraction reflux of fluids into the nose or minor nosebleeds should raise the dentist’s index of suspicion of this condition. Diagnosis is confirmed by getting the patient to hold their nose and blow: air bubbles will be seen at the tooth socket. Small oro-antral fistulas close spontaneously; others require suturing of the mucosal flap.

Fig. 7.8 Projection of the sinus paranasales onto the skull

A Anterior view. B Left lateral view.

The sinus paranasales are air-filled cavities that reduce the weight of the skull. They are subject to inflammation that may cause pain over the affected sinus (e.g., frontal headache due to frontal sinusi tis). Knowing the location and sensory supply of the sinuses is helpful in making the correct diagnosis.

Fig. 7.9 Pneumatization of the sinus maxillaris and frontalis

Anterior view. The sinus frontalis and maxillaris develop gradually during the course of cranial growth (pneumatization), unlike the cellulae ethmoidales, which are already pneumatized at birth. As a result, sinusitis in children is most likely to involve the cellulae ethmoidales (with risk of orbital penetration: red, swollen eye).

Fig. 7.10 Bony structure of the sinus paranasales

Anterior view. The central structure of the sinus paranasales is the os ethmoidale (red). Its lamina cribrosa forms a portion of the anterior skull base. The sinus frontalis and maxillaris are grouped around the os ethmoidale. The meati nasi inferior, medius, and superior of the cavitas nasi are bounded by the accordingly named conchae. The bony ostium of the sinus maxillaris opens into the meatus nasi medius, lateral to the concha nasi media. Below the concha nasi media and above the sinus maxillaris ostium is the bulla ethmoidalis, which contains the cellulae ethmoidales mediae. At its anterior margin is a bony hook, the processus uncinatus, which bounds the sinus maxillaris ostium anteriorly. The concha nasi media is a useful landmark in surgical procedures on the sinus maxillaris and anterior os ethmoidale. The lateral wall separating the os ethmoidale from the orbita is the paper-thin lamina orbitalis (= lamina papyracea). Inflammatory processes and tumors may penetrate this thin plate in either direction. Note: The maxilla forms the floor of the orbita and roof of the sinus maxillaris. In addition, roots of the maxillary dentition may project into the sinus maxillaris.

Fig. 7.11 Cavitas nasi and sinus paranasales

Transverse section viewed from above. The mucosal surface anatomy has been left intact to show how narrow the nasal passages are. Even relatively mild swelling of the mucosa may obstruct the cavitas nasi, impeding aeration of the sinus paranasales.

The glandula pituitaria, located behind the sinus sphenoidalis in the fossa hypophysialis, is accessible via transnasal surgical procedures.

Cavitas Nasi

Fig. 7.12 Right cavitas nasi

A Sagittal section, medial view, with conchae removed to reveal the openings of the ductus nasolacrimalis and the sinus paranasales. B Drainage of the ductus nasolacrimalis and the sinus paranasales (see Table 7.1); arrows indicate flow of mucosal secretions into the cavitas nasi.

Table 7.1 Drainage of the ductus nasolacrimalis and the sinus paranasales

Duct/Sinuses	Via	Drains to
Ductus nasolacrimalis (red)	Canalis nasolacrimalis	Meatus nasi inferior
Sinus frontalis (yellow)	Ductus frontonasalis	Meatus nasi medius
Sinus maxillaris (orange)	Direct	Meatus nasi medius
Cellulae ethmoidales anteriores and mediae (green)
Cellulae ethmoidales posteriores (green)	Direct	Meatus nasi superior
Sinus sphenoidalis (blue)	Direct	Recessus sphenoethmoidalis

Fig. 7.13 Osteomeatal unit (complex)

Coronal section. Arrows indicate flow of mucosal secretions. The osteomeatal unit (complex) is that part of the meatus nasi medius into which the sinus frontalis and maxillaris drain along with the cellulae ethmoidales anteriores and mediae. When the mucosa (ciliated respiratory epithelium) in the cellulae ethmoidales (green) becomes swollen due to inflammation (sinusitis), it blocks the flow of secretions from the sinus frontalis (yellow) and sinus maxillaris (orange) in the osteomeatal unit (red). Because of this blockage, microorganisms also become trapped in the other sinuses, where they may incite an inflammation. Thus, whereas the anatomical focus of the disease lies in the cellulae ethmoidales, inflammatory symptoms are also manifested in the sinus frontalis and maxillaris. In patients with chronic sinusitis, the narrow sites can be surgically widened to establish an effective drainage route.

Fig. 7.14 Ciliary beating and fluid flow in the right sinus maxillaris and frontalis

Schematic coronal sections of the right sinus maxillaris (A) and sinus frontalis (B), anterior view.

Beating of the cilia produces a flow of fluid in the sinus paranasales that is always directed toward the sinus ostium. This clears the sinus of particles and microorganisms that are trapped in the mucous layer. If the ostium is obstructed due to swelling of the mucosa, inflammation may develop in the affected sinus (sinusitis). This occurs most commonly in the osteomeatal complex of the meatus nasi medius.

Fig. 7.15 Normal drainage of secretions from the sinus paranasalis

Left lateral view. The beating cilia propel the mucous blanket over the cilia and through the choana into the pars nasalis pharyngis, where it is swallowed.

Fig. 7.16 Endoscopy of the sinus maxillaris

Anterior view. The sinus maxillaris is not accessible to direct inspection and must therefore be examined with an endoscope. To enter the sinus maxillaris, the examiner pierces the thin bony wall below the inferior concha with a trocar and advances the endoscope through the opening. The scope can then be angled and rotated to inspect all of the mucosal surfaces. Attachment of a suction device also facilitates the drainage of secretions. Drainage of the sinus maxillaris can also be achieved via the Caldwell-Luc procedure (see Fig. 7.17).

Fig. 7.17 Caldwell-Luc Procedure

In the Caldwell-Luc procedure, a window (fenestration) is created in the anterior wall of the sinus maxillaris. It is used to remove teeth or tooth roots that have been displaced during extractions (see Fig 7.7); to remove cysts, polyps, tumors, and other foreign bodies; to close oro-antral fistulas; to reduce facial fractures; and to drain the sinus (rare now due to endoscopy). It can also be used to gain access to the cellulae ethmoidales, the sinus sphenoidalis, and the fossa pterygomaxillaris (which lies behind the sinus maxillaris).

Mucosa of the Cavitas Nasi

Fig. 7.18 Mucosa of the cavitas nasi

A Mucosa of the septum nasi, parasagittal section viewed from the left side. B Mucosa of the right lateral nasal wall, viewed from the left side. C Posterior view through the choanae into the cavitas nasi.

Although the medial wall of the cavitas nasi is smooth, its lateral wall is raised into folds by the three conchae (conchae superior, media, and inferior), which increase the surface area of the cavitas nasi, enabling it to warm and humidify the inspired air more efficiently. They also create turbulence, mixing olfactory stimulants (see p. 118 for nervus olfactorius). The choanae (posterior nasal apertures) (C) are the posterior openings by which the cavitas nasi communicates with the pars nasalis pharyngis. Note the close proximity of the choanae to the tuba auditiva and tonsilla pharyngea in A.

Fig. 7.19 Functional states of the nasal mucosa

Coronal section, anterior view. The function of the nasal mucosa is to warm and humidify the inspired air and mix olfactory stimulants. This is accomplished by an increase of blood flow through the mucosa, placing it in a congested (swollen) state. The mucous membranes are not simultaneously congested on both sides, but undergo a normal cycle of congestion and decongestion that lasts approximately six hours (the right side is decongested in the drawing). Examination of the cavitas nasi can be facilitated by first administering a decongestant to shrink the mucosa.

Fig. 7.20 Histology of the nasal mucosa

The surface of the pseudostratified respiratory epithelium of the nasal mucosa consists of kinocilia-bearing cells and goblet cells, which secrete their mucus into a watery film on the epithelial surface. Serous and sero mucous glands are embedded in the connective tissue and also release secretions into the superficial fluid film. The directional fluid flow produced by the cilia is an important component of the non-specific immune response. If coordinated beating of the cilia is impaired, the patient will suffer chronic recurring infections of the respiratory tract.

Fig. 7.21 Anterior and posterior rhinoscopy

A Anterior rhinoscopy is a procedure for inspection of the cavitas nasi. Two different positions (I, II) are used to ensure that all of the anterior cavitas nasi is examined.

B In posterior rhinoscopy, the choanae and tonsilla pharyngea are accessible to clinical examination. The rhinoscope can be angled and rotated to demonstrate the structures shown in the composite image. Today the rhinoscope is frequently replaced by an endoscope.

Nose & Sinus Paranasales: Histology & Clinical Anatomy

Fig. 7.22 Neurovasculature of the septum nasi

Parasagittal section, left lateral view. The septum nasi is supplied antero superiorly by CN V₁ and posteroinferiorly by CN V₂. It receives blood primarily from branches of the arteriae ophthalmica and maxillaris, with contribution from the arteria facialis (rami septi nasi of the arteria labialis superior).

Fig. 7.23 Neurovasculature of the lateral nasal wall

Left medial view of right lateral nasal wall. The ganglion pterygopalatinum (located in the fossa pterygopalatina but exposed here) is an important relay in the parasympathetic nervous system. The CN V₂ nerve fibers pass through it to the small glandulae nasales of the conchae nasi, along with glandulae palatinae. The anterosuperior portion of the lateral nasal wall is supplied by branches of the arteria ophthalmica and CN V₁. Note: Nervi olfactorii (CN I) pass through thelamina cribrosa to the olfactory mucosa at the level of the concha nasi superior.

Fig. 7.24 Arteries of the septum nasi

Left lateral view of left side of septum. The vessels of the septum nasi arise from branches of the arteriae carotides externa and interna. The anterior part of the septum contains a highly vascularized area called Kiesselbach’s area, which is supplied by vessels from both major arteries. This area is the most common site of significant nosebleed due to anastomoses.

Fig. 7.25 Nerves of the septum nasi

Left lateral view of right lateral nasal wall. The septum nasi receives its general sensory innervation from branches of the nervus trigeminus (CN V). The anterosuperior part of the septum is supplied by branches of the nervus ophthalmicus division (CN V₁) and the rest by branches of the nervus maxillaris division (CN V₂). Bundles of olfactory nerve fibers (CN I) arise from receptors in the olfactory mucosa on the superior part of the septum, pass through the lamina cribrosa, and enter the bulbus olfactorius. (see p. 118 for discussion of nervus olfactorius [CN I]).

Fig. 7.26 Arteries of the right lateral nasal wall

Left lateral view of right lateral nasal wall. The nasal wall is supplied primarily by branches of the arteria ophthalmica (anterosuperiorly) and arteria maxillaris (posteroinferiorly), with contributions from the arteria facialis (alar branches of the ramus lateralis nasi).

Fig. 7.27 Nerves of the right lateral nasal wall

Left lateral view of the right lateral nasal wall. The nasal wall derives its sensory innervation from branches of the nervus ophthalmicus division (CN V₁) and the nervus maxillaris division (CN V₂). Receptor neurons in the olfactory mucosa send their axons in the nervus olfactorius (CN I) to the bulbus olfactorius.

Olfactory System (Smell)

Fig. 7.28 Olfactory system: olfactory mucosa and central connections

Tractus olfactorius viewed in midsagittal section (A) and inferiorly (B). The olfactory mucosa is located in the roof of the cavitas nasi. The olfactory cells (= primary sensory cells) are bipolar neurons. Their peripheral receptor-bearing processes terminate in the epithelium of the nasal mucosa, and their central processes pass to the bulbus olfactorius. The bulbus olfactorius, where the second neurons of the olfactory pathway (mitral and tufted cells) are located, is considered an extension of the telencephalon. The axons of these second neurons pass centrally as the tractus olfactorius. In front of the substantia perforata anterior, the tractus olfactorius widens to form the trigonum olfactorium and splits into the striae olfactoriae lateralis and medialis.

• Some of the axons of the tractus olfactorius run in the stria olfactoria lateralis to the olfactory centers: the amygdala, gyrus semilunaris, and gyrus ambiens. The prepiriform area (Brodmann area 28) is considered to be the primary olfactory cortex in the strict sense. It contains the third neurons of the olfactory pathway. Note: The prepiriform area is shaded in B, lying at the junction of the basal side of the lobus frontalis and the medial side of the lobus temporalis.

• Other axons of the tractus olfactorius run in the stria olfactoria medialis to nuclei in the area septalis (subcallosus), which is part of the limbic system, and to the tuberculum olfactorium, a small elevation in the substantia perforata anterior.

• Yet other axons of the tractus olfactorius terminate in the nucleus olfactorius anterior, where the fibers that cross to the opposite side branch off and are relayed. This nucleus is located in the trigonum olfactorium, which lies between the two striae olfactoriae and in front of the substantia perforata anterior.

Note: None of these three tracts are routed through the thalamus. Thus, the olfactory system is the only sensory system that is not relayed in the thalamus before reaching the cortex. There is, however, an indirect route from the primary olfactory cortex to the neocortex passing through the thalamus and terminating in the pars basalis telencephali. The olfactory signals are further analyzed in these basal portions of the forebrain (not shown).

The olfactory system is linked to other brain areas well beyond the primary olfactory cortical areas, with the result that olfactory stimuli can evoke complex emotional and behavioral responses. Noxious smells induce nausea, and appetizing smells evoke watering of the mouth. Presumably these sensations are processed by the hypothalamus, thalamus, and limbic system via connections established mainly by the fasciculus medialis telencephali and the striae medullares thalami. The fasciculus medialis telencephali distributes axons to the following structures:

• Nuclei hypothalami

• Formatio reticularis

• Nuclei salivatorii

• Nucleus posterior nervi vagi

The axons that run in the striae medullares thalami terminate in the nuclei habenulares. This tract also continues to the brainstem (truncus encephali), where it stimulates salivation in response to smell.

Fig. 7.29 Olfactory mucosa and organum vomeronasale (Jacobson’s organ) (VNO)

The olfactory mucosa occupies an area of approximately 2 cm² on the roof of each cavitas nasi, and 10⁷ primary sensory cells are concentrated in each of these areas (A). At the molecular level, the olfactory receptor proteins are located in the cilia of the sensory cells (B). Each sensory cell has only one specialized receptor protein that mediates signal trans duction when an odorant molecule binds to it. Although humans are microsmatic, having a sense of smell that is feeble compared with other mammals, the olfactory receptor proteins still make up 2% of the human genome. This underscores the importance of olfaction in humans. The primary olfactory sensory cells have a life span of approximately 60 days and regenerate from the basal cells (life-long division of neurons). The bundled central processes (axons) from hundreds of olfactory cells form fila olfactoria (A) that pass through the lamina cribrosa of the os ethmoidale and terminate in the bulbus olfactorius, which lies above the lamina cribrosa. The VNO (C) is located on both sides of the anterior septum nasi. It is an accessory olfactory organ and is generally considered vestigial in adult humans. However, it responds to steroids and evokes subconscious reactions in subjects (possibly influences the choice of a mate). Mate selection in many animal species is known to be mediated by olfactory impulses that are perceived in the VNO.

Fig. 7.30 Synaptic patterns in the bulbus olfactorius

Specialized neurons in the bulbus olfactorius, called mitral cells, form apical dendrites that receive synaptic contact from the axons of thousands of primary sensory cells. The dendrite plus the synapses make up the olfactory glomeruli. Axons from sensory cells with the same receptor protein form glomeruli with only one or a small number of mitral cells. The basal axons of the mitral cells form the tractus olfactorius. The axons that run in the tractus olfactorius project primarily to the olfactory cortex but are also distributed to other nuclei in the central nervous system. The axon collaterals of the mitral cells pass to granule cells: both granule cells and periglomerular cells inhibit the activity of the mitral cells, causing less sensory information to reach higher centers. These inhibitory processes are believed to heighten olfactory contrast, which aids in the more accurate perception of smells. The tufted cells, which also project to the primary olfactory cortex, are not shown.