Pigmented Desmoplastic Trichilemmoma Arising in Nevus Sebaceous: A Potential Mimicker of Pigmented Basal Cell Carcinoma.

Introduction: Trichilemmomas are a form of benign adnexal neoplasm with differentiation toward the follicular outer sheath. Nevus sebaceous (NS) of Jadassohn is a congenital malformation characterized as a nonhereditary hamartoma of the adnexal structures of the skin, mainly the pilosebaceous unit. NS represents a fertile field for the development of secondary adnexal neoplasms, commonly benign but occasionally malignant. To our knowledge, one case of a pigmented desmoplastic trichilemmoma (DT) has been reported in the English literature.

Case presentation: We report a case of a 36-year-old male with pigmented DT that developed on long-standing congenital NS, mimicking pigmented basal cell carcinoma (BCC), which was successfully excised with 4-mm margins.

Conclusion: Pigmented DT may mimic pigmented BCC on clinical and dermatoscopic examination; therefore, histological evaluation is always recommended to confirm the diagnosis.