Abstract
Eleven cases of a nonaneurysmal perimesencephalic subarachnoid hemorrhage (NP-SAH) have been analyzed with special reference to the findings of computerized tomography (CT), magnetic resonance imaging (MRI), and cerebral angiography to know the bleeding site. Among the total number of patients with a nontraumatic subarachnoid hemorrhage (SAH) that the authors' facility has handled, 597 patients underwent cerebral angiography, and the number of SAH cases with an unknown etiology amounted to 27 (4.5%). In 11 of 20 patients with negative SAH angiographic results but with an apparent SAH on CT, the main SAH site was the perimesencephalic cisterns. The dominant SAH site on initial CT was the interpeduncular cistern, and the SAH site on CT from 8 to 21 days after SAH was also the interpeduncular cistern. The SAH sites on MRI from 7 to 11 days after SAH were the interpeduncular cistern and prepontine cistern. Repeated angiograms from 7 to 12 days after SAH showed vasospasms mainly in upper trunk of the basilar artery. These findings suggest that the bleeding site in NP-SAH may be the basilar artery or its branches in the interpeduncular and prepontine cisterns. However, this study was unable to clarify the pathological cause of NP-SAH.
