Choroid plexus papilloma. Light and electron microscopic study

Choroid plexus papilloma (CPP) was observed by light and electron microscopy, using surgically excised tissues in 7 cases and cultivated cells. CPP cells had numerous microvillous processes showing balloon-like features, lysosomes containing haemosiderin, and highly electron-dense irregular granules about 150-300 nm in diameter. Interstitial cells with highly electron-dense cytoplasm inserted their long and thin processes into the invagination of basal plasmalemma of CPP cells, occasionally breaking down the basal lamina. Many of them were located in the intercellular space among CPP cells, sometimes adhering to the ventricular surface of CPP cells. Ruthenium red stain was positive on the surface of CPP cells and was especially intense on the surface of microvilli and cilia. In culture, CPP cells and interstitial cells migrating from the CPP cell mass showed a phagocytic activity after treatment with Latex.