The effects of hydrocephalus upon the developing brain. Histological and quantitative studies of the ependyma and subependyma in hydrocephalic rats.

A suspension of kaolin was injected into the cisterna magna of 44 rats at 2 weeks of age. Animals killed at intervals from 5--19 weeks of age showed varying degrees of hydrocephalus. Light microscopy, scanning and transmission electron microscopy revealed stretching and flattening of the ependymal cells but no significant loss of cilia. Histological evidence of periventricular tissue damage in these chronically hydrocephalic animals was only present when the ventricular dilatation was extensive. A quantitative assessment was made of the ependymal and subependymal cell reactions around the lateral ventricles of the hydrocephalic animals. Although the ependymal cells were clearly stretched around the ventricles, there was no apparent proliferation of these cells. An increase in the total number of subependymal cells was observed in hydrocephalic animals when compared with a series of 39 aged-matched controls. The greatest proliferation was in the dorsal and lateral walls of the ventricles which were the regions most severely stretched by the ventricular dilatation. There is evidence that subependymal cells differentiate into astrocytes and microglia so that proliferation of these cells may be interpreted as a response to continuing and progressive brain damage in chronic hydrocephalus. Such progressive tissue damage could adversely affect the developing brain.