Figure 1: Schematic diagram of the Borden (B) and Cognard (C) dural arteriovenous fistula classification systems. (a) B1–CI; (b) B1–CIIa; (c) B2–CIIb; (d) B2–CIIa + b; (e) B3–CIII; (f) B3–CIV; (g) CV. (1) Artery; (2) cortical vein; (2a) ectasic cortical vein; (3) sinus; (4) thrombus; (5) spinal vein