Venous drainage patterns in perimesencephalic nonaneurysmal subarachnoid hemorrhage

Objective The precise etiology of perimesencephalic nonaneurysmal subarachnoid hemorrhage (P-SAH) has not yet been determined. We decided to compare the venograms of patients with P-SAH with those of patients with aneurysmal SAH (A-SAH) to examine the relationship between P-SAH and venous drainage patterns. Methods We retrospectively studied 18 patients with P-SAH during the past 10 years and 112 patients with ruptured A-SAH during the past 4 years by reevaluating their venograms for possible abnormalities in venous structures, particularly focusing on the basal vein of Rosenthal (BVR). Anatomical variants were classified into three types according to the drainage pathway. Results The location and drainage pathway of the BVR proved to be a significantly more primitive configuration in patients with P-SAH than in those with A-SAH (P < 0.05). On the other hand, physical action including components of the Valsalva maneuver were the cause of nine cases of P-SAH (69.2%) in this case profile. The occurrence rate was significantly higher in the P-SAH group than in the A-SAH group (14.3%) (p < 0.05). Conclusion Our data suggest that failure of longitudinal anastomoses between the primary primitive veins as well as excessive strenuous exertion including components of the Valsalva maneuver plays an important predisposing role in the etiology of P-SAH.