Acute Clinical Decline in Anterior Convexity Dural Arteriovenous Fistula Highlighting the Role of Bridging Vein Anatomy: A Case Report and Literature Review

Convexity dural arteriovenous fistulas (dAVF) are a rare arteriovenous shunt disorder, typically classified as Borden type Ⅲ with cortical venous reflux. We describe the possibility that variations in venous drainage patterns related to lesion location may influence the clinical course of convexity dAVF. An 80-year-old man presented with progressive motor aphasia and dysarthria. Magnetic resonance fluid-attenuated inversion recovery imaging demonstrated hyperintensity in the left frontal lobe. Cerebral angiography revealed a Borden type Ⅲ convexity dAVF at the coronal suture level with retrograde cortical venous drainage. The following day, he experienced a seizure, accompanied by intracerebral hemorrhage (ICH) and worsening venous congestion. Given the rapid progression, middle meningeal artery embolization was performed, followed by surgical shunt disconnection. Postoperatively, motor aphasia and higher cortical dysfunction improved markedly. Histopathological examination revealed no occlusion or remnant of dural veins connected to a venous lake or superior sagittal sinus (SSS), indicating a shunt formation within a normal dural arteriovenous network. The shunt was located near the coronal suture, where bridging veins to the SSS are anatomically sparse. Without compensatory drainage, pial venous reflux (PVR) predominated, resulting in ICH due to worsening venous congestion. These findings suggest that in convexity dAVF, anatomical differences in bridging vein distribution may lead to distinct drainage patterns between anterior and parietal lesions, even within the same Borden type Ⅲ. In particular, cases with predominant PVR may experience rapid clinical deterioration, necessitating prompt intervention.