THE PATHOLOGY OF EXPERIMENTAL OBSTRUCTIVE HYDROCEPHALUS

Acute hydrocephalus was produced in newborn rabbits by the injection of kaolin into the cisterna magna. The light microscopic changes which occurred in the ependyma and periventricular brain tissue were studied. Some animals also received intraventricular injection of Evans blue albumin (EBA) at various times after the kaolin injection to study the permeability of the ependymal lining. There was a progressive dilatation of the lateral ventricles from the second day after the kaolin injection. Marked hydrocephalus was seen after 2 weeks. The white matter of the cerebral hemispheres showed increasing reduction in volume with the degree of hydrocephalus. No destruction of brain tissue, macrophage response, or inflammation were seen. The ependyma adapted remarkably well to the increased intraventricular pressure by extensive flattening and stretching. Apart from occasional and inconstant ruptures at the sites of the ventricular coarctations, no convincing breaks or defects of the ependymal lining were seen. There was a patchy spongy zone beneath the ependyma, possibly indicating oedema of the periventricular white matter due to transventricular movement of cerebrospinal fluid (CSF). Denudation of the ependymal lining is not necessary for the concept of transventricular flow of CSF. No difference was seen in the penetration of EBA into the periventricular tissue between hydrocephalic and control animals. The reduction of the cerebral mantle thickness was probably caused by simple pressure atrophy. This indicates that the changes may to a large extent be reversible if the hydrocephalus is treated within reasonable time.