Melanotic neuroectodermal tumor of the epididymis in infancy: case report and review of the literature.

Melanotic neuroectodermal tumor of infancy (MNTI) is a rare, benign tumor that usually involves the upper or lower jaw, but it may also arise in other sites. We describe a case of MNTI located in the left epididymis of a 6-month-old boy. Left orchiectomy was performed. Immunohistochemical and ultrastructural studies revealed two types of cells: small, poorly differentiated cells that were positive for neuron-specific enolase protein and vimentin, and larger epithelial cells that were positive for melanoma antigen (HMB45) and frequently contained large and elongated melanosomes, similar to those described in retinal pigmented epithelium. At 12 months of follow-up, no recurrences or metastases were seen. Primary involvement of the epididymis has been previously reported in only 16 cases. Immunohistochemical and ultrastructural studies suggest that the neoplasm is of neural crest origin.