Spontaneous dissecting aneurysms of the basilar artery presenting with a subarachnoid hemorrhage. Report of two cases.

A spontaneous dissecting aneurysm of the basilar artery is a rare disorder, usually presenting with ischemia rather than a subarachnoid hemorrhage (SAH). Two cases are described of a dissecting aneurysm of the basilar artery presenting with an SAH. Vertebral angiography revealed a double lumen to the basilar artery. Magnetic resonance (MR) imaging detected the intramural hematoma. One patient was treated conservatively, and the other underwent operative intervention with wrapping of the aneurysm. The usefulness of MR imaging in the diagnosis and the treatment options are discussed.