Type II: DAVF draining into a sinus. Insufficient antegrade venous drainage and reflux. The insufficiency of the venous drainage may be due to stenosis or occlusion of the sinus draining a moderate flow rate DAVF, or to a very high flow rate DAVF which cannot be drained by a normal or even enlarged sinus. Depending on the retrograde venous drainage, three subtypes are distinguished: |
Type IIa: retrograde venous drainage into sinus(es) only |
Type IIb: retrograde venous drainage into cortical vein(s) only |
Type IIa+b: retrograde venous drainage into sinus(es) and cortical vein(s) |
Type III: DAVFs draining directly into a cortical vein without venous ectasia |
Type IV: DAVFs draining into a cortical vein with a venous ectasia >5 mm in diameter and three times larger than the diameter of the draining vein. |
Type V: DAVFs (intracranial) draining into spinal perimedullary veins |