A Ruptured Aneurysm Arising at the Leptomeningeal Collateral Circulation from the Extracranial Vertebral Artery to the Posterior Inferior Cerebellar Artery Associated with Bilateral Vertebral Artery Occlusion

We report an extremely rare case of a small ruptured aneurysm of the leptomeningeal collateral circulation from the vertebral artery (VA) to the posterior inferior cerebellar artery (PICA); this aneurysm was associated with bilateral VA occlusion. A 72-year-old woman with sudden headache, nausea, and subarachnoid hemorrhage (SAH) was admitted to our hospital. On admission, no evidence of cerebral signs or cranial nerve palsy was found. Computed tomography imaging showed SAH predominantly in the posterior fossa, and digital subtraction angiography revealed bilateral VA occlusion and the left VA aneurysm located proximal to the VA union. In addition, a small aneurysm was observed at the leptomeningeal collateral circulation located between the extracranial left VA and the left PICA. The patient underwent radical surgery on the day of the onset of the symptoms associated with SAH. However, the VA aneurysm was unruptured and surgically trapped. The small aneurysm arising at the leptomeningeal collateral circulation was ruptured during the surgery and was electrocoagulated; the collateral circulation was preserved, and no neurologic deficits were observed. The postoperative course was uneventful. SAH with the occlusion of major vessels should be diagnosed with utmost caution to allow preoperative neurologic and radiological assessments.