Dural Arteriovenous Fistulas of the Foramen Magnum Region: Clinical Features and Angioarchitectural Phenotypes

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.

Arterial anatomy of a typical type 1 FMR AVF. TOF-MRA (A) of the skull base shows abnormal flow-related enhancement in the right hypoglossal canal, corresponding to a fistula (asterisk). Arterial supply from the contralateral ascending pharyngeal artery (hypoglossal branch) crosses the foramen magnum and drains via the IJV. Relative anatomy: an anterior-posterior DSA with injection of the left ascending pharyngeal artery (B) shows hypertrophied arterial channels (double-sided arrow). Lateral DSA of the right ICA (C) shows supply to the fistula (asterisk) from the meningohyposphyseal trunk (MHT). D, Lateral DSA of the right vertebral artery (V₃) shows direct contribution to fistula (asterisk) and drainage via the IJV. NMT indicates neuromeningeal trunk; MS, marginal sinus.