FIG 2.

Modified grading system for FMR-AVFs shown in 4 patients having undergone lateral occipital artery (OA) injection DSA. Type 1 shows unrestricted drainage via the IJV (curved arrow) without reflux. Type 2 shows both antegrade drainage (curved arrow) and sinus reflux (dashed arrow, inferior petrosal sinus). Type 3 lesions are differentiated by the presence of cortical venous reflux, in this case, pontine perforating veins (black arrow) in addition to sinus drainage (white arrow). Type 4 lesions have restricted, exclusive drainage via cortical veins (arrowheads) without a coexisting sinus drainage pathway.