Melanotic medulloblastoma. A case report with immunohistochemical and ultrastructural examination.

A melanotic medulloblastoma is reported with electron microscopic and immunohistochemical findings. The cerebellar tumor had seeded through the cerebrospinal fluid to cerebrum and spinal cord, spread through the dura, and metastasized to the lungs. It consisted of (i) anaplastic cells with slight neuronal differentiation, but without the fibrillary background of neuroblastomas, and (ii) epithelial islands pigments with melanin. The latter participated in the spread through the subarachnoid space, but did not extend beyond the dura. Electron microscopy revealed in the pigmented cells tight junctions and oculo-cutaneous melanin, including premelanosomes. The anaplastic cells had undistinguished organelles and only small junctions. On immunohistochemistry, the cytoplasm of the anaplastic cells was positive for neuron-specific enolase and neurofilament, and some of the nuclei were positive to S-100, confirming neuronal differentiation. The cells did not stain for glial fibrillary acidic protein, carcinoembryonic antigen, cytokeratin, alpha fetoprotein, vimentin, and epithelial membrane antigen. The melanotic cells were negative to all reagents tested, even to S-100 protein. The presence of oculo-cutaneous melanin and of neuronal elements indicate a neuroectodermal or neural crest origin.