Variant deep cerebral venous drainage in idiopathic subarachnoid hemorrhage

Variant deep cerebral venous drainage, primarily involving the basal vein of Rosenthal (BVR), may be a cause of idiopathic subarachnoid hemorrhage (SAH). In this study, deep venous drainage was compared between 13 patients with idiopathic SAH and 35 control patients with aneurysmal SAH diagnosed by digital subtraction angiography (DSA). Venous return was evaluated by DSA on 25 sides in patients with idiopathic SAH and 67 sides in patients with aneurysmal SAH, and the relationship between the BVR and the vein of Galen was classified into 3 categories: types A (normal continuous), B (normal discontinuous), and C (primitive variant). The occurrence rates of the three categories were: idiopathic SAH, type A 24%, type C 40%; and aneurysmal SAH, type A 49.3%, type C 10.4% (p = 0.003). Combined bilateral venous drainage was classified as normal combination (AA), discontinuous combination (AB, BB), and primitive combination (AC, BC, CC), with rates: idiopathic SAH, normal 0%, primitive 58.3%; and aneurysmal SAH, normal 42.4%, primitive 21.2%. Venous drainage on either the left or right side was more commonly type C (primitive) in idiopathic SAH (p = 0.006). Three patients with left-right differences in hematoma distribution on brain computed tomography had types A, B, and C on the SAH dominant side in one patient each. No clear trend was observed between hematoma distribution and primitive variant side. Some patients with idiopathic SAH had thick hematoma in the basal cistern. Further, 3 patients with idiopathic SAH had an aneurysmal pattern, rather than a perimesencephalic pattern. All these patients had type C either on the left or right side. Therefore, although the mechanism of involvement of venous drainage in idiopathic SAH is unknown, hemorrhage is not limited to a perimesencephalic pattern. The present findings support a previous hypothesis that variant venous drainage is involved in the occurrence of idiopathic SAH. The absence of a normal combination of venous drainage is an important factor to diagnose idiopathic SAH.