Polypoid dermal dendrocytic hamartoma in a giant congenital melanocytic nevus

Giant congenital melanocytic nevus (CMN) might be complicated by the development of several tumor types, mainly melanoma and rhabdomyosarcoma, but also poorly differentiated neoplasms. Striking polypoid exophytic masses occasionally result from neuroectodermal and neuromesenchymal hamartomatous overgrowths, which lends support to the concept of pluripotential melanoblastomatous and neurocristic origin of these lesions. The present report describes what appears to be a unique example of dermal hamartomatous polypoid CD34(+) fibrogenic proliferation devoid of melanin, namely a dendrocytoma, surrounded by the melanocytes from the nevus, located in the skin of the scrotum against a background of giant CMN. The differential diagnosis included dermatofibrosarcoma protuberans, giant-cell fibroblastoma, angiofibroma, Bednar tumor, other types of dermal dendrocytic hamartoma, and neurocristic cutaneous hamartoma. This case lends support to the proposed neurocristic origin of dermal fibrogenic cells.