In the past, several possible explanations for idiopathic subarachnoid hemorrhage (ISAH) have been proposed; however, neuroimaging studies have never provided conclusive data about the structural cause of the bleeding. The aim of this study is to determine whether there are anatomic differences in the deep cerebral venous drainage in patients with ISAH compared with those with aneurysmal subarachnoid hemorrhage (ASAH) and those without intracranial hemorrhage.METHODS
We reviewed the venous phase of carotid digital angiograms of 100 consecutive patients who had a final diagnosis of ISAH. We also analyzed the angiograms of a control group of 112 patients with ASAH and the angiograms of a nonhemorrhagic group of 25 patients having incidental aneurysms. The anatomic variants of the basal vein of Rosenthal (BVR) on both sides were classified into the following types: Type A (normal continuous), in which the BVR is continuous with the deep middle cerebral veins and drains mainly into the vein of Galen; Type B (normal discontinuous), in which there is discontinuous venous drainage, anterior to the uncal vein and posterior to the vein of Galen; and Type C (primitive), which drains mainly to veins other than the vein of Galen. We calculated the proportions to analyze the differences in the type of venous drainage between patients with ISAH, patients with ASAH, and patients without hemorrhage. χ2 statistics were used to search for differences.RESULTS
Types A and C venous drainage were present in 23.8 and 32.3%, respectively, of patients with ISAH compared with 58.7 and 15.4%, respectively, in the ASAH group and 57.5 and 5%, respectively, in the nonhemorrhagic group (P < 0.001). A primitive variant was present in at least 1 hemisphere in 38 patients with ISAH (41.8% of the cases) compared with 24 patients with ASAH (21.4%) and 2 patients (8%) in the nonhemorrhagic group (P < 0.001).CONCLUSION
In patients with ISAH, deep cerebral venous drainage more commonly drains directly into dural sinuses instead of via the vein of Galen compared with patients with ASAH and patients without intracranial hemorrhage. The way in which this venous configuration might influence bleeding remains unknown.