Trichoadenoma associated with an intradermal melanocytic nevus: a combined malformation

Melanocytic nevi have been associated with epidermal hyperplasia, adnexal hyperplasia with follicular and sebaceous differentiation, cysts, and tumors of epidermal or adnexal origin. We report a combined cutaneous hamartoma in a 29-year-old woman that comprised a trichoadenoma within an intradermal melanocytic nevus. Clinical diagnosis was a malignant transformation of a melanocytic nevus. Histopathologically, multiple keratinous cysts together with solid islands or masses of eosinophilic epithelial cells were closely intermingled with the nevus cells. Occasional nests of basaloid cells were present. Although to our knowledge this association has not been previously reported, it is worth considering that trichoadenoma and desmoplastic trichoepithelioma are the two ends of a spectrum of lesions. This combined hamartoma reported herein is important because growth of these lesions could be clinically misinterpreted as malignant transformation of a preexisting lesion. Histologic study will reveal the correct diagnosis in such cases.