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Gross appearance of a trichoepithelioma
Varioant erosive form of trichoepithelioma, easily confused with pemphigus
Cytological smear of a trichoepithelioma

A benign tumor showing differentiation to all three segments of the hair follicle, but in which trichogenesis is present, incomplete or abortive.

This is a rare neoplasm in cats.

Gross Appearance

  • Intradermal masses
  • Often exophytic
  • Ranging in size from 1-5 cm in diameter
  • Many are ulcerated
  • Multiple grey-white foci of keratinous material are separated by thin connective tissue trabeculae on cut section
  • Cystic
  • Infiltrative type associated with sclerotic change.


  • Considerable variation in the histopathologic appearance of these tumors
  • Often the tumor is a multilobulated intradermal mass
  • Involvement of the subcutaneous tissue may be found, particularly in infiltrative forms of the tumor
  • Common feature of all these tumors is trichogenic differentiation
  • In some tumors the proliferating epithelial elements are associated with a stroma that may be either fibrotic or mucinous
  • Islands of epithelial cells consist of basaloid cells with differentiation to internal and external root sheath
  • Thickened basal lamina at the periphery
  • Matrical differentiation with accumulation of shadow cells within the center of the epithelial islands is often present


Many keratinized squamous epithelial cells, cellular debris, moderate numbers of degenerate and non-degenerate neutrophils, occasional macrophages, and occasional cholesterol crystals.

Differential diagnosis

Histology is require to accurately diagnose and distinguish this benign tumour with other forms of epithelial tumours, including keratinising acanthomas, trichoblastoma, pilomatricoma, tricholemmoma, Epithelial lymphoma, calcinosis cutis in Cushing's syndrome and sebaceous adenoma.