On the pathology of experimental hydrocephalus.

Acute hydrocephalus was produced in newborn rabbits by 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 ependyma. 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. Neither destruction of brain tissue nor macrophage response or inflammation were seen. The ependyma adapted remarkably well to the increased intraventricular pressure by extensive flattening and stretching. No convincing breaks or ruptures were seen. There was a patchy spongy zone beneath the ependyma, probably indicating oedema of the periventricular white matter due to transventricular absorption of the cerebrospinal fluid (CSF). Denudement 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 morphological changes may to a large extent be reversible if the hydrocephalus is properly treated within reasonable time. The role of morphological changes in the pathophysiology of hydrocephalus if briefly commented upon in relation to certain aspects of human hydrocephalus.