Midterm Follow-Up of 20 Consecutive Patients with Nonaneurysmal Subarachnoid Hemorrhage of Unknown Origin in a Single-Center: Two Cases of De Novo Development of Dural Arteriovenous Fistula

Background and purpose: The mechanisms and prognosis of underlying subarachnoid hemorrhage of unknown origin remain unclear. Previous investigators have suggested a relationship between nonaneurysmal perimesencephalic subarachnoid hemorrhage and venous abnormalities like a primitive venous drainage of the basal vein of Rosenthal. We report the outcome of a midterm follow-up of 20 consecutive patients with nonaneurysmal subarachnoid hemorrhage of unknown origin, and 2 patients in whom the development of new dural arteriovenous fistulas after subarachnoid hemorrhage of unknown origin were detected during follow-up. Methods: All patients who were admitted to our hospital for nontraumatic subarachnoid hemorrhage between April 2008 and March 2016 were retrospectively analyzed. Results: Of 705 patients included in the study, 20 (2.8%) were diagnosed with nontraumatic subarachnoid hemorrhage of unknown origin. During the follow-up periods, there was no rebleeding. Although 18 patients did not show any vascular abnormalities, the other 2 patients were diagnosed with dural arteriovenous fistula. Both fistulas were successfully treated with endovascular embolization. Conclusions: Subarachnoid hemorrhage of unknown origin had a low incidence rate, and its clinical course was excellent without rebleeding. Although no vascular abnormalities were observed during the patients' initial admission, venous lesions might have been involved in both subarachnoid hemorrhages and delayed dural arteriovenous fistulas. Here, the possible pathogenesis is discussed with a review of the literature.