Figure 8. Drawings illustrate a classification scheme for transverse-sigmoid sinus dural AVFs that is based on venous drainage patterns: Grade 1, antegrade sinus drainage without venous restriction or cortical venous reflux; Grade 2, antegrade and retrograde sinus drainage with or without cortical venous reflux; Grade 3, retrograde sinus drainage with cortical venous reflux; and Grade 4, cortical venous reflux only. (Reprinted, with permission, from reference 11.)