Electron microscopic observations on malignant choroid plexus papilloma.

Biopsy material from two cases of histologically proven malignant choroid plexus papilloma was studied by electron microscopy. Both tumours differed from benign papillomas in showing poorly differentiated areas with numerous mitoses. Even in such areas, however, a number of ultrastructural features characteristic of normal choroid plexus tissue were observed in both the cases, including cilia, microvilli, a continuous basement membrane and capillary endothelial fenestration. Such findings may be helpful in establishing the primary origin of malignant tumours in the choroid plexus, especially where light microscopy of poorly differentiated biopsy samples makes diagnosis uncertain.