Ultrastructural evidence for CSF production by a choroid plexus papilloma.

A choroid plexus papilloma (CPP) removed from a child with communicating hydrocephalus was studied with the electron microscope. In addition to the usual organelles, the neoplastic epithelial cells contained polypoid microvilli, cilia, coated pinocytotic vesicles, and apical tight junctions. The basal surfaces were consistently juxtaposed to large capillaries lined by fenestrated endothelium. The fine structural details of the tumor were essentially the same as those of normal CP and thus appeared ideally suited for an active secretory function. Two additional features in this tumor were tubular bodies in the endothelium and well developed pericytes. The present findings provide strong evidence for cerebrospinal fluid production by CPP, a phenomenon that has long been suggested by clinical observation.