[Computed tomographic evaluation due to ruptured intracranial aneurysms in the posterior fossa]

From April, 1978 through December, 1984, computed tomographic (CT) findings were carefully examined in 34 cases of initial subarachnoid bleeding due to a single ruptured aneurysm in the posterior fossa. All of the patients were hospitalized within 3 days of the onset of symptoms. High-density areas, which indicate the presence of subarachnoid clots, were evaluated in the interhemispheric and Sylvian fissures and the interpeduncular, prepontine, ambient, and quadrigeminal cisterns. The CT data suggest that hematomas in the four cisterns are thicker than those in the supratentorial subarachnoid spaces. Only one patient had an intracerebral hematoma. Hydrocephalus accompanied aneurysms of the posterior fossa more frequently than those of the anterior circulation.