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Shape on Low Power

• Epidermis
  • Regular acanthosis, 25
  • Lobular proliferation, 29
  • Reticulated proliferation, 35
  • Central pore, 42
  • Epidermal perforation, 46
• Dermis
  • Circular islands, 49
  • Cords/tubules and comma shapes, 53
  • Space with a lining, 59
  • Papillations, 70
  • Polypoid (dome-shaped), 77
  • Square/rectangular, 82
  • Palisading reactions, 88
  • Pseudoepitheliomatous hyperplasia above abscesses, 93
  • Pink ball (see Chapter 6)

Bowen disease

• 

  

  Epidermal acanthosis
• Parakeratosis
• Full-thickness disorder of keratinocytes with atypical cells and mitoses
• Basal layer may focally appear normal (“eyeliner” sign) (arrow)

  Clear cell acanthoma
  

  

  

  

• Epidermal acanthosis
• Clear cells well-demarcated from the normal epidermis and adnexal keratinocytes
• Parakeratosis above clear cells

  Psoriasis
  

  

  

• Epidermal acanthosis
• Parakeratosis
• Neutrophils in stratum corneum (asterisk)
• Hypogranulosis
• Thinned suprapapillary plates (long arrow)
• Dilated vessels in papillary dermis (short arrows)

  Key differences
  

  

  (a)

  

  (b)

  

  (c)

  1. Bowen disease: disordered keratinocytes and atypical mitoses
  2. Clear cell acanthoma: pale/clear keratinocytes well-demarcated from normal epidermis
  3. Psoriasis: confluent parakeratosis above thickened epidermis, neutrophils in stratum corneum, normal keratinocytes, thin suprapapillary plates, dilated vessels

  Inverted follicular keratosis
  

  

  

• Lobular proliferation
• Normal-appearing keratinocytes with some arranged in squamous eddies

  Molluscum contagiosum
  

  

  

  

• Lobular proliferation
• Blue-gray hue to some of the keratinocytes
• Large, pink cytoplasmic inclusions (Henderson-Paterson bodies)

  Poroma
  

  

  

  

• Lobular proliferation (can be reticulated)
• Uniform blue cells with interspersed ducts (arrows)
• Fibrotic or hyalinized stroma with dilated vessels

  Seborrheic keratosis, acanthotic
  

  

  

• Lobular proliferation
• Acanthosis of epidermis
• Pseudohorn cysts
• No ducts

  Trichilemmoma
  

  

  

  

• Lobular proliferation
• Proliferation composed of pale/clear cells
• Peripheral palisading (long arrow) with thickened basement membrane (short arrow)

  Key differences
  

  

  (a)

  

  (b)

  

  (c)

  

  (d)

  

  (e)

  1. Inverted follicular keratosis: squamous eddies of normal keratinocytes
  2. Molluscum contagiosum: intracytoplasmic pink inclusions (Henderson-Paterson bodies)
  3. Poroma: uniform blue cells with interspersed ducts, hyalinized stroma
  4. Seborrheic keratosis: pseudohorn cysts
  5. Trichilemmoma: pale/clear keratinocytes with peripheral palisading and thickened basement membrane

  Fibroepithelioma of Pinkus
  

  

  

  

• Reticulated proliferation
• Strands of basaloid cells in a fibrovascular stroma
• Some hints of palisading of cells (arrow)

  Fibrofolliculoma
  

  

  

• Reticulated proliferation
• Fibrotic stroma adjacent to the hair follicle has reticulated strands of epithelium
• This entity has overlap with trichodiscoma (most consider these a spectrum of the same entity)

  Nevus sebaceus of Jadassohn
  

  

  

  

• Reticulated proliferation
• Sebaceous glands, basaloid proliferations (arrow) connect to the epidermis
• Apocrine glands may be seen deep
• Absent terminal hairs in mature stage

  Seborrheic keratosis, reticulated
  

  

  

  

• Reticulated proliferation
• Strands of banal keratinocytes, often pigmented
• Interspersed pseudohorn cysts

  Syringofibroadenoma
  

  

  

• Reticulated proliferation
• Strands of banal, round cells
• Interspersed ducts

  Tumor of the follicular infundibulum
  

  

  

• Reticulated proliferation
• Pale cells in columns with “windows” of dermis in between
• Peripheral palisading

  Key differences
  

  

  (a)

  

  (b)

  

  (c)

  

  (d)

  

  (e)

  

  (f)

  1. Fibroepithelioma of Pinkus: strands of basaloid epithelium in fibrovascular stroma
  2. Fibrofolliculoma: hair follicle with adjacent fibrotic stroma and reticulated epithelium
  3. Nevus sebaceus: proliferation of epidermis connecting to sebaceous lobules and basaloid proliferations
  4. Seborrheic keratosis, reticulated: reticulated strands of banal keratinocytes, often pigmented; interspersed pseudohorn cysts
  5. Syringofibroadenoma: strands of uniform, round cells with interspersed ducts
  6. Tumor of the follicular infundibulum: pale cells in columns with “windows” of dermis in between

  Dilated pore of Winer
  

  

  

• Central pore
• Invaginated epidermis is acanthotic

  Pilar sheath acanthoma
  

  

  

  

• Central pore
• Invaginated epidermis is acanthotic and has areas resembling outer root sheath with peripheral palisading around slightly pale cells

  Trichofolliculoma
  

  

  

• Central pore
• Invaginated epidermis connects to a primary hair follicle
• Multiple secondary hair follicles radiating away from the central follicle

  Key differences
  

  

  (a)

  

  (b)

  

  (c)

  1. Dilated pore of Winer: acanthotic epidermis
  2. Pilar sheath acanthoma: epidermal acanthosis and areas resembling outer root sheath
  3. Trichofolliculoma: primary follicle and surrounding secondary follicles

  Elastosis perforans serpiginosa
  

  

  

  

• Epidermal perforation
• Elongated claw (epidermal rete) gripping thin, glassy, eosinophilic elastic fibers and debris
• Altered elastic fibers are thinner than the collagen fibers in the dermis

  Reactive perforating collagenosis
  

  

  

• Epidermal perforation
• Shallow cup-shaped architecture
• Pink collagen fibers extend vertically through epidermis

  Key differences
  

  

  (a)

  

  (b)

  

  (c)

  

  (d)

  1. Elastosis perforans serpiginosis: elongated rete forming a claw (tortuous channel); case courtesy of Whitney High, MD, JD
  2. Reactive perforating collagenosis: shallow, broad cup-shaped architecture
  3. Calcinosis cutis, perforating: chunky, bluish material (see page 264) at the base of an ulcer

  4. Granuloma annulare, perforating: palisading histiocytes around collagen with mucin (see page 89)

     Note Other entities may also perforate the epidermis, for example, chondrodermatitis nodularis helicis, pseudoxanthoma elasticum.

  Adenoid cystic carcinoma
  

  

  

• Circular dermal islands
• Islands contain basaloid cells with a cribriform pattern of duct-like spaces filled with amorphous material

  Cylindroma
  

  

  

  

• Circular dermal islands
• Islands contain basaloid cells surrounded by a thick pink basement membrane (arrow)
• Islands arranged like a “jigsaw puzzle”

  Trichoadenoma
  

  

• Circular dermal islands
• Islands of epithelium with central flaky keratin (horn cysts)
• Interspersed basaloid cords

  Key differences
  

  

  (a)

  

  (b)

  

  (c)

  1. Adenoid cystic carcinoma: cribriform pattern of duct-like structures
  2. Cylindroma: puzzle-like arrangement, thick/pink basement membrane
  3. Trichoadenoma: numerous horn cysts

  Desmoplastic trichoepithelioma
  

  

  

• Cords/tubules and comma shapes in dermis
• Numerous horn cysts (long arrow) in fibrotic stroma
• Tubules of two-layered epithelium (short arrow)
• Calcification often present
• Confined to dermis

  Metastatic breast carcinoma
  

  

  

  

  

• Cords/tubules and comma shapes in dermis and below
• Tubules of single-layered (“Indian filing” – long arrow) and multi-layered epithelium
• Some cells forming gland-like structures (short arrow)
• Other metastatic carcinomas may look like this – need clinical history; immunohistochemistry may be helpful

  Microcystic adnexal carcinoma
  

  

  

• Cords/tubules and comma shapes in dermis
• Comma shapes with duct-like spaces
• Deeply infiltrative (fills dermis)
• Perineural involvement

  Morpheaform basal cell carcinoma
  

  

  

  

• Cords/tubules and comma shapes in dermis
• Tubules of epithelium composed of basaloid cells with hints of peripheral palisading
• New collagen forming around islands (arrow)
• Deeply infiltrative

  Syringoma
  

  

  

• Cords/tubules and comma shapes in dermis
• Restricted to upper dermis
• “Tadpoles” of epithelium with duct-like structures in heads (arrow)
• Darker cells at periphery, clear cells in center
• Eosinophilic cuticle lining lumina
• No horn cysts

  Key differences
  

  

  (a)

  

  (b)

  

  (c)

  

  (d)

  

  (e)

1. Desmoplastic trichoepithelioma: horn cysts, no clear cells, circular areas of epithelium surround keratin
2. Metastatic breast carcinoma: single filing of atypical cells, deeply infiltrative
3. Microcystic adnexal carcinoma: like syringoma with tadpole-like structures but deeply infiltrative, perineural involvement
4. Morpheaform basal cell carcinoma: infiltrative cords of basaloid cells with hints of peripheral palisading; may have some duct-like structures (but less than c)
5. Syringoma: superficial tadpoles with clear cells

   Apocrine hidrocystoma
   

   

   

• Space with a lining
• Lining composed of an inner layer of cells with decapitation secretion (long arrow) and a compressed layer of myoepithelial cells (short arrow)

  Auricular pseudocyst
  

  

  

• Space with a lining
• “Lining” is not a true epithelial layer but is cartilage
• Centrally, there is degeneration of cartilage

  Branchial cleft cyst
  

  

  

• Space with a lining
• Lining composed of squamous or sometimes cuboidal/columnar epithelium often with squamous metaplasia
• Prominent lymphoid follicles in wall

  Cutaneous ciliated cyst
  

  

  

• Space with a lining
• Lining composed of cuboidal/columnar epithelium with cilia (arrows)

  Cutaneous endometriosis
  

  

  

• Space with a lining
• Spaces embedded in a fibrovascular stroma (endometrial stroma)
• Lining composed of crowded blue cells
• Hemosiderin deposits common in stroma

  Dermoid cyst
  

  

  

• Space with a lining
• Lining composed of squamous epithelium
• Walls contain adnexal structures

  Epidermoid cyst
  

  

  

  

• Space with a lining
• Lining composed of squamous epithelium with a granular layer (arrow)
• Cyst contents composed of flakes of keratin

  Pilar cyst
  

  

  

  

• Space with a lining
• Lining composed of squamous epithelium without a granular layer
• Cyst contents composed of dense pink keratin

  Steatocystoma
  

  

  

• Space with a lining
• Lining composed of layered epithelium with a bright pink crenulated keratin (arrow)
• Sebaceous glands in wall

  Key differences
  

  

  (a)

  

  (b)

  

  (c)

  

  (d)

  

  (e)

  

  (f)

  

  (g)

  

  (h)

  

  (i)

  

  (j)

  1. Apocrine hidrocystoma: decapitation secretion
  2. Auricular pseudocyst: degeneration surrounded by cartilage
  3. Branchial cleft cyst: prominent lymphoid follicles in wall
  4. Cutaneous ciliated cyst: columnar epithelium with cilia; no structures in wall
  5. Cutaneous endometriosis: fibrovascular stroma with glands
  6. Dermoid cyst: sebaceous glands and other adnexal structures in wall
  7. Epidermal inclusion cyst: epithelium with granular layer, flakes of keratin in center
  8. Glomuvenous malformation (glomangioma): monomorphous, cuboidal blue cells (see also glomus tumor on page 282)
  9. Pilar cyst: epithelium without granular layer, dense keratin in center

  10. Steatocystoma: crenulated keratin lining the cyst; sebaceous glands in wall

      Note Bronchogenic cysts are uncommon, and are diagnosed by clinical history and the presence of columnar epithelium +/− cilia, +/− cartilage in wall; venous lakes are common and are composed of flattened endothelial cells with erythrocytes in the space.

  Aggressive digital papillary adenocarcinoma
  

  

  

  

• Papillated dermal tumor
• Disordered layers of epithelium in large papillations with some tubules
• Variable cytological atypia and mitotic figures
• Acral location

  Erosive adenomatosis of the nipple (nipple adenoma)
  

  

  

  

• Papillated dermal tumor
• Nipple can sometimes be identified by fascicles of smooth muscle in dermis
• Circular islands, some cystic, and tubules
• Compressed myoepithelial cells at periphery of islands/tubules
• Decapitation secretion often evident
• Resembles syringocystadenoma papilliferum (stromal plasma cells [arrows]) or tubular apocrine adenoma

  Hidradenoma papilliferum
  

  

  

  

• Papillated dermal tumor
• Finger-like projections have cores of collagen/fibroblasts (arrow)
• No connection to epidermis

  Papillary eccrine adenoma
  

  

  

  

• Islands of epithelium with papillated projections
• With or without epidermal connection
• Duct-like spaces lined by eosinophilic cuticle
• Overlaps with tubular apocrine adenoma

  Syringocystadenoma papilliferum
  

  

  

  

• Papillated dermal tumor
• Papillations contain numerous plasma cells (arrow)
• Tumor often connected to epidermis

  Tubular apocrine adenoma
  

  

  

  

• Papillated dermal tumor
• Evidence of decapitation secretion
• Overlaps with papillary eccrine adenoma

  Key differences
  

  

  (a)

  

  (b)

  

  (c)

  

  (d)

  

  (e)

  

  (f)

  1. Aggressive digital papillary adenocarcinoma: large tumor, atypical cells and mitoses piled up
  2. Florid papillomatosis (erosive adenomatosis) of the nipple (nipple adenoma): resembles syringocystadenoma papilliferum but fewer plasma cells; nipple may be identified by smooth muscle bundles in dermis
  3. Hidradenoma papilliferum: thin papillations with fibrovascular cores
  4. Papillary eccrine adenoma: islands of epithelium with papillated areas
  5. Syringocystadenoma papilliferum: fat papillations with plasma cells in cores
  6. Tubular apocrine adenoma: decapitation secretion and papillations within islands

  Accessory digit
  

  

  

  

  

• Polypoid shape
• Acral skin (thick stratum corneum with stratum lucidum [long arrow])
• Dermal nerve bundles (short arrows)

  Accessory nipple
  

  

  

• Polypoid shape
• May see a slight invagination of surface epidermis with underlying sebaceous glands
• Surface epidermis often slightly acanthotic and hyperpigmented
• May see mammary ducts or apocrine glands deep
• Dermis with numerous smooth muscle bundles (arrows)

  Accessory tragus
  

  

  

• Polypoid shape
• Thin epidermis
• Vellus hairs (arrows)
• Cartilage not always present
• Differential diagnosis of numerous vellus hairs
  • – Eyelid/earlobe/sometimes facial skin
  • – Vellus hair nevus

  Digital fibrokeratoma
  

  

  

• Polypoid shape
• Acral skin
• Fibrovascular stroma (thick collagen [arrows])

  Key differences
  

  

  (a)

  

  (b)

  

  (c)

  

  (d)

  1. Accessory digit: nerve bundles in the dermis
  2. Accessory nipple: sebaceous glands, mammary ducts or apocrine glands, smooth muscle bundles in the dermis
  3. Accessory tragus: vellus hairs in the dermis

  4. Digital fibrokeratoma: collagen in the dermis

     Note Other entities may also be polypoid; for example, intradermal nevus, neurofibroma, fibrous papule, etc.

  Morphea
  

  

  

  

• Square/rectangular shape
• Thick, pink smudgy collagen in dermis
• Plasma cells around vessels
• Atrophic or absent adnexal structures

  Necrobiosis lipoidica
  

  

  

  

  

• Square/rectangular shape
• Altered, reddened collagen (necrobiosis) layered with inflammation
• Giant cells and plasma cells are prominent

  Normal back skin
  

  

  

  

• Square/rectangular shape
• Normal-appearing collagen bundles in dermis
• No increased mucin

  Scleredema
  

  

  

  

• Square/rectangular shape
• Slight widening of space between collagen due to mucin (arrow)
• No increase in fibroblasts

  Scleromyxedema
  

  

  

• Square/rectangular shape
• Slight widening of space between collagen due to mucin (long arrow)

• Increased fibroblasts (short arrows)

  Note Lichen myxedematosus is histologically similar but clinically different.

  Note Nephrogenic systemic fibrosis may show similar findings but may have deeper involvement.

  Key differences
  

  

  (a)

  

  (b)

  

  (c)

  

  (d)

  

  (e)

  1. Morphea: thickened bundles of collagen with loss of fenestrations between collagen bundles
  2. Necrobiosis lipoidica: reddened collagen sandwiched between layers of inflammatory cells (giant cells, plasma cells)
  3. Normal back: normal-sized collagen bundles, no increased mucin
  4. Scleredema: mucin between collagen
  5. Scleromyxedema: mucin and increased fibroblasts

  Gout
  

  

  

  

• Palisading of histiocytes around amorphous white-gray substance with a feathery edge

  Granuloma annulare
  

  

  

• Palisading of histiocytes around altered collagen, basophilic mucin (long arrow)
• Lymphocytes around vessels (short arrow)

  Necrobiotic xanthogranuloma
  

  

  

  

  

• Palisading of histiocytes and bizarre, multinucleated giant cells around foci of necrosis
• Scattered Touton giant cells
• Cholesterol clefts, plasma cells, and/or lymphoid follicles may be present

  Rheumatoid nodule
  

  

  

  

• Palisading of histiocytes around central pink fibrin
• The reaction is often deep

  Key differences
  

  

  (a)

  

  (b)

  

  (c)

  

  (d)

  

  (e)

  1. Gout: central white-gray feathery material
  2. Granuloma annulare: central altered collagen interspersed with blue mucin
  3. Rheumatoid nodule: central pink fibrin
  4. Necrobiosis lipoidica: altered “red” collagen surrounded by giant cells, plasma cells (see page 83)
  5. Necrobiotic xanthogranuloma: bizarre, multinucleated giant cells; Touton giant cells

  Blastomycosis
  

  

  

  

• Pseudoepitheliomatous hyperplasia above abscesses
• Yeast forms (arrow) that classically show broad-based budding

  Chromomycosis
  

  

  

• Pseudoepitheliomatous hyperplasia above abscesses
• Brown-colored septate rounded “hot cross buns” (Medlar bodies, sclerotic bodies, copper pennies) (arrow)

  Coccidioidomycosis
  

  

  

  

  

• Pseudoepitheliomatous hyperplasia above abscesses
• Large (~80-200 micron) spherules containing endospores (arrows)

  Key differences
  

  

  (a)

  

  (b)

  

  (c)

  1. Blastomycosis: ~8–30 micron yeast form (arrow)
  2. Chromomycosis: ~5–12 micron Medlar bodies

  3. Coccidioidomycosis: ~80-200 micron spherules with endospores

     Note Paracoccidioidomycosis (~6–60 micron Mariner’s wheel; an uncommon infection in the United States), sporotrichosis (organisms usually not evident in biopsies), and tuberculosis verrucosa cutis may also show this pattern.