Cognard et al’s classification system considers venous drainage patterns, the direction of flow, the presence of venous ectasia, and the clinical presentation (22).
| Type | Subclassification | Description |
| I | Drain directly into the dural venous sinus with antegrade flow | |
| II | a | Drain directly into the dural venous sinus with retrograde flow |
| b | Drain directly into the dural venous sinus with antegrade flow and reflux into cortical veins | |
| a+b | Drain directly into the dural venous sinus with retrograde flow and reflux into cortical veins | |
| III | Drain directly into the cortical veins without venous ectasia | |
IV | Drain directly into the cortical veins with venous ectasia | |
| V | Drain into spinal perimedullary veins |
In the original paper (22), Cognard et al reported the following clinical presentations associated with different classifications:
- Intracranial hypertension: 20% of type II DAVFs were associated with intracranial hypertension due to retrograde flow into the sinus (22).
- Hemorrhage: 10% of type II, 40% of type III, and 65% of type
IVDAVFs were associated with hemorrhage due to reflux into the cortical veins (22). - Progressive myelopathy: 50% of type V DAVFs were associated with progressive myelopathy (22).
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