Nonaneurysmal Perimesencephalic Subarachnoid Hemorrhage Associated with an Anomalous Anastomotic Cisternal Vein

A 54-year-old woman with no relevant medical history presented with severe headache, nausea, and vomiting for 8 days. Imaging examination revealed a subarachnoid hemorrhage in the left interpeduncular cistern without aneurysms. Computed tomography angiography and digital subtraction angiography found an anomalous vein near the site of the hemorrhagic clots, indicating abnormalities in cerebral venous drainage that provided an anastomosis between the drainage system of the deep middle cerebral, petrosal, and lateral mesencephalic veins. In the primitive pattern, the basal vein of Rosenthal drains into the lateral mesencephalic vein and to the petrosal sinus. This anomalous flow may predispose to subarachnoid hemorrhage, emphasizing the association between nonaneurysmal perimesencephalic hemorrhage and venous anomalies.