TRICHOEPITHELIOMA
Etiology.
Trichoepithelioma shows a spectrum of histopathologic features reflecting mainly differentiation toward hair and hair follicle, particularly follicular germs.This neoplasm is therefore best regarded as a distinct variant of trichoblastoma (described in the section Trichoblastoma).
Clinical Findings.
Three distinctive forms of trichoepitheliomas are recognized; namely, solitary, multiple, and desmoplastic.
Solitary trichoepithelioma occurs mainly as a small (5 to 8 mm in diameter), skin-colored papule situated on the face, especially around the nose, upper lip, and cheeks of adults. Occasional lesions develop on the trunk, neck, scalp, and lower extremities.
Multiple trichoepitheliomas present usually in adolescents as numerous, small papules distributed on the face, with predilection for the area around the nasolabial folds, forehead, chin, and preauricular area . A few patients reveal plaques, nodules, or tumors due to coalescing of several lesions. Multiple trichoepitheliomas are mostly transmitted as an autosomal dominant trait in patients with Brooke-Spiegler (epithelioma adenoides cysticum) syndrome. In this syndrome, patients show predisposition for developing multifocal cylindromas, spiradenomas, and milia. Multiple trichoepitheliomas have also rarely been associated with a number of other systemic conditions, including Rombo syndrome (atrophoderma, milia, hypotrichosis, basal cell carcinomas, and peripheral vasodilatation), systemic lupus erythematosus, and myasthenia gravis.
Histopathology.
This is a dome-shaped, sharply circumscribed lesion composed of aggregations of relatively monomorphic basaloid (germinative) cells in the upper dermis surrounded by abundant fibrous stroma with intrastromal clefts The basaloid aggregations are mainly arranged in a cribriform pattern but may show other architectural patterns, including nodular, racemiform, and retiform. They typically reveal peripheral palisading and several foci with rudimentary follicular papillae and germs. In some lesions, other findings include infundibulocystic structures, shadow cells, sebaceous glands, amyloid, calcification, melanin pigmentation, and mucin deposition. A lymphohistiocytic infiltrate with small foreign-body granulomas is sometimes present.
Treatment.
Surgery is usually effective in removing solitary lesions. However, surgical treatment of multiple trichoepitheliomas is generally disappointing. Alternative therapies have included cryotherapy, electrodesiccation, and carbon dioxide laser