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

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.