Ruptured vertebrobasilar junction aneurysm supplied by reversed flow from the anterior spinal artery: Illustrative case report.

Background and ImportanceIn patients with vertebral artery (VA) occlusion, spontaneous flow reversal may occur in the anterior spinal artery (ASA) as a source of compensatory supply to the posterior circulation. Turbulent flow and increased flux through these small arteries may predispose to luminal damage and intracranial aneurysm formation. We report a novel case of a ruptured ASA-VA junction aneurysm in a patient with chronic bilateral VA occlusion, successfully treated with endovascular embolization.Clinical PresentationA 62-year-old female with uncontrolled hypertension presented with acute-onset headache, emesis, neck stiffness, and decreased level of consciousness. Head computed tomography demonstrated diffuse cisternal subarachnoid hemorrhage with intraventricular extension and ventriculomegaly. Computed tomography angiography showed left VA atresia and chronic right VA occlusion just distal to the posterior inferior cerebellar artery origin, as well as a complex, bilobed aneurysm at the ASA-VA junction. Angiography demonstrated flow reversal from the ASA into the distal stump of the occluded right VA, which in turn filled the aneurysm. Of note, the patient's posterior circulation was predominantly supplied by the dilated ASA, and associated collaterals from ASA and right VA stump. The aneurysm was accessed and embolized using superselective microcatheterization over a soft microguidewire through the right cervical VA perforators supplying retrograde flow into and through the ASA.ConclusionASA-VA aneurysms are exceedingly rare, and generally associated with atypical flow dynamics. Dynamic treatment strategies may be needed, especially in the setting of subarachnoid hemorrhage.