Desmoplastic trichilemmoma of the facial region mimicking invasive carcinoma.

Trichilemmoma is a hamartomatous proliferation arising from cells of hair follicle. Its desmoplastic variant simulates an invasive carcinoma. In this tumor, the cell of origin seems to be located in the superficial level of the hair follicle just below the basement membrane at the sebaceous gland level. We present a similar case which presented with an asymptomatic nodular lesion in the region above the upper lip on left side. Fine needle aspiration cytology raised the cytological possibility of a malignancy for which the lesion was excised. On histopathology the lesion was diagnosed as desmoplastic trichilemmoma. The case highlights the difficulty encountered in differentiating a benign adnexal tumor from malignant lesion based on cytology alone. Moreover, the extensive desmoplasia on histopathology raises the suspicion of invasive malignancy which requires to be carefully excluded. The superficial features of trichilemmoma and lack of cellular atypia is a useful diagnostic clue in such a situation. Positivity of CD34 can also be used to differentiate from basal cell carcinomas. The case reported here had a solitary lesion, but follow up is required for development of more lesions or multiple hamartomas in other organs as a part of Cowden's disease.