General Considerations

•hair follicle tumors account for < 1% of skin tumors in cats and 5% of canine skin tumors

•types: trichoepithelioma, pilomatrixoma, tricholemmoma, and trichofolliculoma

Trichoepithelioma (Hair Matrixoma)

General Considerations

•trichoepithelioma accounts for 80% of hair follicle tumors (and up to 2%-3% of all feline skin tumors)

•benign tumor derived from primitive hair matrix cells that show differentiation to either mature or incompletely developed hair follicles

•17.5% have histologic features of malignancy

•however, biologic behaviour is usually benign with local tumor recurrence and metastasis rare

•site: dorsal lumbar and lateral thoracic region

•gross appearance is similar to basal cell carcinoma but some are cystic and contain keratin

•intradermal mass with overlying epidermis atrophic, hairless and often ulcerated secondary to trauma

•treatment: surgery

•prognosis: excellent

Feline Trichoepithelioma

•breed predisposition: Siamese

•in cats, trichoepithelioma is well-circumscribed, > 5 cm in diameter and usually occur over dorsal lumbar area although others report small, slow-growing tumors with a predilection for the head and back

Canine Trichoepithelioma

•mean age 9.3 years

•breed predisposition: Golden Retriever, GSD, and Bassett Hound

•histologically unique form with mucinous degeneration reported in the Golden Retriever

Pilomatricoma

•benign tumors arising from hair matrix cells and particularly pilar matrix cells

•mean age 8.2 years

•breed predisposition: Kerry Blue Terrier and Miniature Poodle

•sites: shoulder and lumbrosacral region

•slow growing, well-encapsulated, and often mineralized with 33% cystic and 33% hyperpigmented

•malignant pilomatricoma is rare (2 cases reported) with metastasis to neurologic structures

•treatment: surgery

•prognosis: excellent

Tricholemmoma and Trichofolliculoma

•rare