Basaloid follicular hamartoma with trichoblastomatous proliferations

Basaloid follicular hamartomas (BFH) are rare, benign, adnexal lesions with diverse clinical presentations. Previous studies documented BFHs with fibroepithelioma of Pinkus-like proliferations, or proliferations that resemble trichoepitheliomas.

We report on a patient with linear, unilateral BFH and extensive trichoblastomatous proliferations involving the right arm, torso, and leg. An 18-year-old female presented with multiple, hyperkeratotic, linear nodules and plaques limited to her right side from the shoulder to the leg. The lesions had existed since birth and gradually increased over time.

The lesions contained hyperpigmented, exophytic nodules with acanthosis, pseudoepitheliomatous hyperplasia, focally associated with hyperkeratosis, and squamous eddies. Some areas contained trichoepithelioma-like proliferations, or large nodules of basaloid cells with numerous cystic spaces, marked hyperpigmentation, and melanophages. The diagnosis was linear, unilateral BFH with an unusual trichoblastomatous component.

While trichoblastomatous proliferations could occur in a BFH, to our knowledge this finding has not been reported.