Melanotic neuroectodermal tumor of infancy (MNTI) in the epididymis. A case report with immunohistological studies and special consideration of malignant features.

Melanotic neuroectodermal tumors of infancy (MNTI) are uncommon, usually benign neoplasms, most frequently found in the maxilla. These tumors are extremely rare in the epididymis. Only 18 cases with this site of origin are documented. We report on the third epididymal MNTI with some morphological characteristics of malignancy but favorable clinical outcome. The 2 cm large tumor of a 6-month-old male infant showed large epitheloid cells in the center and small neuroblastoma-like cells at the periphery. Despite invasion of lymphatics there is no evidence of relapse or metastases during 4 years of follow-up. Immunohistochemically, the large tumor cells were distinctly positive for cytokeratin, vimentin, GFAP, the melanoma marker NKI-C3, NSE, and S100. The small tumor cells were only slightly positive for GFAP, NKI-C3, NSE, and S100 but they were negative for cytokeratin and vimentin. Neurofilament and chromogranin could not be proved in the tumor.