SPONTANEOUS VENTRICULAR RUPTURE IN HYDROCEPHALUS, WITH SUBTENTORIAL CYST FORMATION.

The anatomical features of hydrocephalus are fairly well known, and a growing knowledge of the pathology suggests that in most if not all cases the ventricular dilatation can be explained by obstruction to the circulation of the cerebro-spinal fluid. It is not always easy to identify the site or cause of the obstruction, but a common place is in the narrows of the midbrain where the aqueduct may be compressed by a benign proliferation of the subependymal glia or by a tumour of the brain stem, pineal gland or vermis cerebelli. As the prognosis and treatment differ considerably in these various conditions, we commonly look to ventriculography for help in diagnosis. For various reasons, the interpretation of air shadows in this region is not always easy, or indeed possible, and we feel that any additional information about the pathological possibilities should be of importance. This report deals chiefly with two cases of hydrocephalus in which the dilatation of the lateral ventricles was accompanied by rupture of the wall of the ventricle in the region of the vestibule, and the formation of a cyst-like space under the tentorium communicating with the lateral ventricle. The site of the rupture was identical in the two cases, and the ventriculographic appearances were similar. In both cases the hydrocephalus resulted from aqueduct obstruction, in one by proliferation of the subependymal glia and in the other by a fibrillary astrocytoma of the brain stem. We have also included the pathological report of a case of hydi ccephalus due to adhesive arachnoiditis in which an early stage in the development of this process was seen. Our interest in this abnormality began with an earlier case of stenosis of the aqueduct which had produced great dilatation of the third ventricle. The distended suprapineal recess protruded as a cyst-like swelling beneath the splenium, insinuating itself between the lower surfaces of the occipital lobes, and the upper surface of the cerebellum. Since then we have seen such dilatations in ventriculograms on a number of occasions and had come to regard the presence of a large suprapineal recess as evidence for an intrinsic lesion of the brain stem (benign stricture or tumour) as opposed to an extrinsic lesion such as a tumour of the superior vermis or of the pineal gland. The recess may be dilated in cases of obstruction in the distal part of the fourth ventricle too, but in these cases the aqueduct and fourth ventricle are generally dilated and it is fairly easy to demonstrate them in ventriculograms. In our first case, a large air-shadow beneath the tentorium was thought to be such a dilated suprapineal recess until it was shown at necropsy to be in communication with the lateral and not with the third ventricle.