Cognard classification of dural arteriovenous fistulas

Last revised by Dr Rohit Sharma on 15 Feb 2022

The Cognard classification of dural arteriovenous fistulas (dAVF) correlates venous drainage patterns with increasingly aggressive neurological clinical course and stratifies the risk of intracerebral hemorrhage. It was first described in 1995 1 and at the time of writing (July 2016) is probably the most widely used classification system for dural arteriovenous malformations. 

An alternative and also popular classification system, also proposed in 1995, is the Borden classification 3. It is a little simpler (only 3 grades) and only takes into account the site of fistula and the presence or absence of cortical venous drainage. It does not assess the direction of flow or the presence of venous ectasia. It has been suggested that it does not capture the differences in terms of the rate of hemorrhage reflected in the Cognard classification 2,4

The Cognard classification divides dural arteriovenous fistulas into 5 types according to the following features: 

  • location of fistula
  • presence of cortical venous drainage
  • direction of flow
  • presence of venous ectasia
  • type I
    • confined to sinus
    • antegrade flow
    • no cortical venous drainage/reflux
  • type II
    • IIa 
      • confined to sinus
      • retrograde flow (reflux) into sinus
      • no cortical venous drainage/reflux
    • IIb
      • drains into sinus with reflux into cortical veins
      • antegrade flow
    • IIa+b
      • drains into sinus with reflux into cortical veins
      • retrograde flow
  • type III
    • drains directly into cortical veins (not into sinus) drainage (40% hemorrhage)
  • type IV
    • drains directly into cortical veins (not into sinus) drainage with venous ectasia (65% hemorrhage)
  • type V
    • spinal perimedullary venous drainage, associated with progressive myelopathy

In terms of prognosis, fistulas can be divided broadly into benign and aggressive lesions as follows 5

  • benign = types I and IIa (lack of cortical venous drainage)
  • aggressive = everything else
    • annual risk of non-hemorrhage neurological deficit = 6.9%
    • annual risk of intracranial hemorrhage = 8.1%
    • combined annual mortality rate = 10.4%

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Cases and figures

  • Case 1: Cognard type IV
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  • Case 2: Cognard type V
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