Why Intraosseous Arteriovenous Fistulas Can Lead to Acute Subdural Hematomas: A Case Report and Literature Review.

Intraosseous arteriovenous fistulas are rare vascular anomalies, with an increasing number of reports describing successful endovascular treatments in recent years. Although some cases of acute subdural hematoma caused by intraosseous arteriovenous fistulas have been reported, the precise mechanism remains unclear. In this study, we present a case of surgical treatment for an intraosseous arteriovenous fistula with acute subdural hematoma. A 58-year-old woman presented to our hospital with a sudden headache and nausea. Computed tomography revealed a left acute subdural hematoma with an abnormal diploic space in the frontal bone. Digital subtraction angiography confirmed an intraosseous arteriovenous fistula supplied by the middle meningeal artery and draining into the diploic vein. Because of concerns about potential tumor involvement, direct surgery was performed. Intraoperatively, vascularized tissue surrounding the fistula extended through the dural defect and connected to the subdural space, suggesting a possible cause of the acute subdural hematoma. The feeder and draining vein were dissected and removed along with the abnormal tissue. Histopathological analysis revealed fibrous tissue with hemorrhage and increased vascularity but no tumorous changes. Postoperative angiography confirmed successful arteriovenous fistula occlusion, and the patient recovered with minimal neurological deficit. This case suggests that intraosseous arteriovenous fistulas may cause acute subdural hematoma owing to the anatomical feature of vascularized tissue around the fistula extending through the dural defect into the subdural space.