Fig. 1.

Schematic drawing of the dural arteriovenous fistula (dAVF) at the posterior medial part of the foramen magnum region (FMR). The occipital sinus (OS) and the marginal sinus (MS) are anatomically variable and usually have inconsistent structures. The shunted pouch is located around the scattered structure of the OS and MS. The bridging vein (BV), which communicates between the FMR and the vein of inferior cerebellar peduncle or the medial posterior medullary vein rarely connects to the scattered OS or MS in the posterior medial portion. This BV works as the single and main drainer of the high-flow dAVF located in the posterior medial part of the FMR