Melanotic papilloma of the choroid plexus: report of a case with implications for pathogenesis.

A case of pigmented choroid plexus papilloma removed from the 4th ventricle of a 43-year-old man is reported. The tumor showed histologic, immunophenotypic, and ultrastructural features of neoplastic choroid plexus epithelium. There was no evidence of melanosomal activity or neurosecretion. The pigment consisted of an intimate association of lipofuscin and neuromelanin, indicating autocatalytic peroxydation of the former as a putative way of melaninogenesis. The low proliferation rate of the tumor together with immunohistochemical evidence of inactivation of p53 protein suggest a delayed turnover of neoplastic cells as a possible source of lipofuscin accumulation.