Early CT features of ruptured cerebral aneurysms of the posterior cranial fossa.

This report describes our retrospective evaluation of CT features of the acute phase in 34 cases of ruptured cerebral aneurysms of the posterior cranial fossa. The results are as follows. 1. Examination of cisternal haematoma distribution revealed that SAH had extended to the supra- and infratentorial cisterns in 28 cases (82%). There were only 6 cases (18%) in which SAH was confined to the posterior cranial fossa only but even when there was subarachnoid haematoma in both the supra- and infratentorial cisterns, thick haematomas were seen at the periphery of the brain stem. In cases of vertebral artery-posterior inferior cerebellar artery aneurysms (VA-PICA AN), haematomas in the ambient cistern were thicker on the aneurysm side. In addition, in cases of basilar artery-bifurcation (BA-Bifurcation AN) and basilar artery-superior cerebelli artery aneurysms (BA-SCA AN), there were many thick, high-density haematomas in the interpeduncular cistern. 2. The rate of intracerebral haemorrhage was extremely low (1 patient). 3. The rate of intraventricular haemorrhage was high, and these haemorrhages demonstrated a reflux pattern. 4. The rate of hydrocephalus was high (76.5%) in comparison with that noted in association with SAH due to the rupture of anterior circulation aneurysms.