Pilar and sebaceous neoplasms

Chapter 4

Pilar and sebaceous neoplasms

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.


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.

Desmoplastic trichoepithelioma

Table 4-2

Characteristics of desmoplastic trichoepithelioma versus morpheaform basal cell carcinoma

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Apr 26, 2016 | Posted by in Dermatology | Comments Off on Pilar and sebaceous neoplasms
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Characteristic Desmoplastic trichoepithelioma Morpheaform basal cell carcinoma
Paisley-tie pattern Yes Sometimes superficially