Case of the month. May 1996--hydrocephalus in a 9 month old infant.

A 9 month old infant presented with hydrocephalus. MRI studies revealed a large cystic space with a nodule that was bright on T-1 weighted images and dark on T-2 weighted images. It was bright with contrast enhancement. The surgical specimen was noted to be dark black. Microscopic examination revealed a benign papillary tumor consistent with a choroid plexus papilloma which was heavily pigmented with melanin. Immunohisto-chemical stains were consistent with a choroid plexus papilloma, but they also showed many epithelial cells to be positive for HMB-45. Ultrastructural studies demonstrated melanosomes and pre-melanosomes in cells with well-delineated basal lamina. This is the first case to demonstrate melanosomes in a benign choroid plexus papilloma. Previously reported cases of pigmented lesions of the choroid plexus either contained neuromelanin in the benign examples or melanosomes in two cases of choroid plexus carcinomas.