THE EPENDYMA IN CHRONIC HYDROCEPHALUS

H-Tx rats produce congenitally hydrocephalic offspring with varying se verity of the condition. We used moderately hydrocephalic rats without evident clinical signs of hydrocephalus and normal controls from the same stock when they were at least 1.5 years old. Macroscopic anatomy was studied by MRT and in fixed brain slices and the ultrastructure of the ependyma, with REM. Apart from markedly stretched areas, where th e ependyma was totally destroyed and subependymal structures directly exposed to the CSF, the density of ependymal microvilli and of tufts o f cilia was reduced in proportion to the ventricular distension of a g iven area. A supraependymal ''network'' - never seen before in acute h ydrocephalus - was found, whose purpose is probably to prevent further ventricular enlargement. We conclude that even in arrested hydrocepha lus the ependymal sequelae of hydrocephalus are similar to those of th e acute stage, illustrating the extremely limited potenctial for recov ery, but the organism seems nevertheless to react with an internal sta bilization of the ventricular system.