Pilar and sebaceous neoplasms

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Chapter 4

Pilar and sebaceous neoplasms

Dirk M. Elston

Pilar neoplasms

Pilar neoplasms differentiate towards (resemble) various parts of the normal hair follicle. They are named according to what they resemble. Before reading this chapter, review the discussion of hair anatomy in Chapter 1. Blue pilar tumors differentiate towards elements of the inferior segment of the hair follicle. Red pilar tumors differentiate towards the isthmus and infundibulum. Clear cell tumors differentiate towards the glycogenated outer root sheath.

Benign trichoblastomas are large basaloid follicular neoplasms. The tumor islands resemble basal cell carcinoma, but the stroma resembles the normal fibrous sheath of the hair follicle. Trichoepitheliomas and lymphadenomas are distinctive forms of benign trichoblastoma. Trichogerminomas are a type of trichoblastoma with differentiation towards the hair germ. Basal cell carcinoma is the most common malignant counterpart of a benign trichoblastoma. Some trichoblastic carcinomas arising in long-standing trichoblastomas have been very aggressive tumors with metastases.

Trichoepithelioma

Trichoepitheliomas commonly present as multiple small papules in the nasolabial folds. The multiple type is inherited in an autosomal-dominant fashion. Each papule is composed of basaloid islands in a fibroblast-rich stroma with papillary mesenchymal bodies. Horn cysts and calcification are common. Small clefts may occur between collagen fibers of the tumor stroma, but not between the tumor epithelium and stroma. Papillary mesenchymal bodies are round collections of plump mesenchymal cells resembling those in the follicular papilla.

Table 4-1

Characteristics of trichoepithelioma versus basal cell carcinoma

Characteristic	Trichoepithelioma	Basal cell carcinoma
Basaloid cells	Yes	Yes
Peripheral palisading	Yes	Yes
Finger-like and cribriform	Yes	Sometimes
Stroma	Concentric, fibroblast-rich	Myxoid
Mucin	In tumor islands only, none in stroma	Metachromatic mucin in stroma
Papillary mesenchymal bodies	Common	Rare
Horn cysts	Common	Rare
Calcification	Common	Rare
Clefts	Between collagen fibers within stroma	Between epithelium and stroma
CD34 staining	Strong staining in stroma	+/−
BCL-2 staining	Periphery of islands	Strong, diffuse
CK20+ Merkel cells	Present in tumoral islands	Absent in tumoral islands

Pearls

• Multiple trichoepitheliomas (epithelioma adenoides cysticum) inherited as autosomal-dominant trait

• Brooke–Spiegler syndrome: multiple trichoepitheliomas and cylindromas

• Rombo syndrome: milia, hypotrichosis, trichoepitheliomas, basal cell carcinoma, atrophoderma, vasodilation with cyanosis

Fig 4-4 Trichoepithelioma

Fig 4-5 Basal cell carcinoma for comparison

Desmoplastic trichoepithelioma

Table 4-2

Characteristics of desmoplastic trichoepithelioma versus morpheaform basal cell carcinoma

Characteristic	Desmoplastic trichoepithelioma	Morpheaform basal cell carcinoma
Paisley-tie pattern	Yes	Sometimes superficially
Stroma	Red, sclerotic	Red, sclerotic
Horn cysts	Common	Occasional
Calcification	Common	Rare
Clefts	Between collagen fibers within stroma	Between epithelium and stroma
Central dell	Yes	No
Age	Younger	Older
Clinical appearance	Firm doughnut	Scar-like

Table 4-3

Characteristics of desmoplastic trichoepithelioma versus microcystic adnexal carcinoma

Characteristic	Desmoplastic trichoepithelioma	Microcystic adnexal carcinoma
Paisley-tie pattern	Yes	Yes
Stroma	Red, sclerotic	Often red, sclerotic
Horn cysts	Common	Common
Calcification	Common	Rare
Lymphoid aggregates	Rare	Typical
Perineural extension	No	Yes
Clinical appearance	Firm doughnut	Plaque on upper lip, cheek, chin
Central dell	Typical	Absent

Table 4-4

Characteristics of desmoplastic trichoepithelioma versus syringoma

Characteristic	Desmoplastic trichoepithelioma	Syringoma
Paisley-tie pattern	Yes	Yes
Stroma	Red, sclerotic	Red, sclerotic
Horn cysts	Common	May occur
Calcification	Common	Rare
Central dell	Typical	Absent
Shape	Broad	Small and round
Clinical appearance	Firm doughnut	Small papules

Pearl

Paisley-tie tumors

• Desmoplastic trichoepithelioma: doughnut-shaped tumor on the cheek of a young female

• Microcystic adnexal carcinoma: firm plaque on the upper lip, medial cheek, or chin

• Morpheaform basal cell carcinoma: scar-like lesion in older patient

• Eruptive syringomas: chest and back or penis, commonly on skin type VI

• Syringomas: small papules on lower lids, very common with Down’s syndrome and in Asian females

Fig 4-6 Desmoplastic trichoepithelioma

Fig 4-7 Morpheaform basal cell carcinoma for comparison

Fig 4-8 Lymphadenoma

Lymphadenoma (adamantinoid trichoblastoma)

Key features

• Tumor islands with 1–2 layers of basaloid cells peripherally

• Centers of each island composed of clear cells/inflammatory cells

Fibrofolliculoma

Key features

• Fibrous pink orb or amphophilic fibromucinous orb

• Epithelial strands radiating outward from central follicle-like structure

• No hair fibers

In fibrofolliculomas, the strands of epithelium are not well enough differentiated to form hair fibers. No bulb, inner or outer root sheath is present. The strands of epithelium may have an anastomosing pattern. Trichodiscomas are simply fibrofolliculomas cut in a plane of section that does not reveal the epithelial strands.

Pearl

Birt–Hogg–Dubé syndrome

• Multiple fibrofolliculomas, “trichodiscomas,” and “acrochordons” (all three are probably fibrofolliculomas cut at various angles)

• Chromophobe renal carcinoma, renal oncocytoma, spontaneous pneumothorax

Fig 4-9 Fibrofolliculoma

Fig 4-10 Trichofolliculoma

Trichofolliculoma

Key features

• Many small hair follicles emptying into a central large follicular infundibulum (momma and her babies)

• Each small hair follicle has a bulb and root sheath, and produces a hair fiber

• Central infundibulum contains many small hair shafts

• Clinically, there is a tuft of hairs protruding from a central pore

Trichofolliculomas demonstrate miniature follicles converging on a central infundibulum (fingers of fully formed follicles forming follicular fibers). Some examples are embedded in an eosinophilic fibrous orb of stroma.

Trichoadenoma

Key features

• Multiple red doughnuts in the dermis, each resembling a follicular infundibulum

• Often in pairs resembling eyeglasses or toasted oat cereal

Fig 4-11 Trichoadenoma

Basaloid follicular hamartoma

Key features

• Resembles infundibulocystic basal cell carcinoma histologically

• Often multiple with autosomal-dominant inheritance

• Sometimes segmental Blaschkoid distribution

Fig 4-12 Basaloid follicular hamartoma

Differential Diagnosis

Infundibulocystic basal cell carcinoma can appear identical histologically. The two are best distinguished clinically.

Dilated pore of Winer

Key features

• Resembles a dilated follicular infundibulum

• Small radiating red finger-like epithelial projections

Fig 4-13 Dilated pore of Winer

Pilar sheath acanthoma

Key features

Pilar sheath acanthoma has been described as a “pore of Winer on steroids”

Fig 4-14 Pilar sheath acanthoma

Trichilemmoma

Key features

• Often a warty surface

• Smooth lobules of clear glycogenated cells hanging down from the epidermis

• Peripheral palisading

• Outlined by a thick glassy eosinophilic “vitreous” basement membrane

Trichilemmomas resemble the glycogenated outer root sheath of the hair follicle. When multiple, they may be a marker for Cowden’s syndrome.

Differential Diagnosis

Trichilemmomas are composed of lobules of clear glycogenated cells that hang down from the surface epidermis. A clear cell acanthoma is a thickened area of the epidermis. In clear cell acanthoma, a glycogenated pale segment of epidermis is sharply demarcated from the surrounding skin. Neutrophils are noted throughout the lesion and in the overlying crust. There is no thickening of the basement membrane zone.

Fig 4-15 Trichilemmoma (BMZ, basement membrane zone)

Desmoplastic trichilemmoma

Key features

• Smooth outline with surrounding glassy basement membrane

• Centrally, broken into jagged islands separated by dense pink stroma

Sebaceous neoplasms

Nevus sebaceus of Jadassohn (organoid nevus)

Postpubertal nevus sebaceus of Jadassohn

Key features

• “Broad, bald, bumpy, and bubbly”

• Present at birth, becomes cerebriform at puberty

• Dilated apocrine glands in underlying dermis

• Hyperkeratosis, acanthosis, and papillomatosis common

• Secondary tumors, especially syringocystadenoma papilliferum and small trichoblastomas, are common

Fig 4-16 Desmoplastic trichilemmoma

Fig 4-17 Postpubertal nevus sebaceus of Jadassohn

Postpubertal cerebriform lesions of nevus sebaceus of Jadassohn appear as broad, alopecic (bald), acanthotic and papillomatous (bumpy) lesions with large sebaceous lobules (bubbly) and dilated apocrine glands.