The aim of this study was to examine the clinical characteristics and angiographic findings of spontaneous idiopathic subarachnoid hemorrhage (ISAH) and to compare these with those of aneurysmal SAH (ASAH). We retrospectively reviewed the clinical characteristics and venograms of 118 consecutive patients with ISAH during the past 10years for possible abnormalities in venous structures. Also, 57 patients with ASAH during the past 4years were examined. Patients with ISAH showed low frequency of hypertension and no patient suffered from an episode of re-bleeding, or delayed ischemic deficits. Physical actions, including varieties of the Valsalva maneuver, were the causes of ISAH in 17 (29.8%) patients. Compared with patients with ASAH, patients with ISAH showed a significant difference in the drainage patterns of the basal vein of Rosenthal (BVR) (p=0.001). In addition, whereas a linearly decreasing trend toward the primitive type was evident in ASAH, each drainage pattern was distributed evenly in ISAH (linear by linear association, p=0.000). In this study, the primitive drainage pattern of BVR has a relationship with ISAH compared to ASAH. The way in which this venous configuration might influence bleeding remains unknown.
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