====== Cognard classification ======

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There are numerous [[Dural arteriovenous fistula]] classifications. [[Borden]] and [[Cognard]] are amongst the
more widely used.

The [[Cognard]] classification of [[dural arteriovenous fistula]]s correlates venous drainage patterns with increasingly aggressive neurological clinical course. It was first described in [[1995]]
((Cognard C, Gobin YP, Pierot L, Bailly AL, Houdart E, Casasco A, Chiras J,
Merland JJ. Cerebral dural arteriovenous fistulas: clinical and angiographic
correlation with a revised classification of venous drainage. Radiology. 1995
Mar;194(3):671-80. PubMed PMID: 7862961.
)). 

Probably the most widely used classification system for [[dural arteriovenous malformation]]s. 

Correlates venous drainage patterns with increasingly aggressive neurological clinical course.

===== Structure =====

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


{{::duralarteriovenousfistulaclassification.jpg|}}

An alternative classification system is the Borden classification proposed in 1995, which although a little simpler (only 3 grades) does not capture differences which exist in terms of rate of haemorrhage reflected in the Cognard classification.
((Intracranial Vascular Malformations and Aneurysms. Springer. (2008*) ISBN:354032920X.))
((Davies MA, Ter Brugge K, Willinsky R et-al. The natural history and management of intracranial dural arteriovenous fistulae. Part 2: aggressive lesions. Interv Neuroradiol. 2012;3 (4): 303-11.))

Type I - confined to [[venous sinus]] wall, typically after thrombosis.

Type II

IIa - confined to sinus with reflux (retrograde) into sinus but not cortical veins

===== Cognard Type IIb dural arteriovenous fistula =====

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Drains into [[sinus]] with reflux (retrograde) into cortical veins (10-20% haemorrhage)

Type III - drains direct into cortical veins (not into sinus) drainage  (40% haemorrhage)

Type IV - drains direct into cortical veins (not into sinus) drainage with venous ectasia (65% haemorrhage)

[[Cognard Type V Dural Arteriovenous Fistula]].

===== Outcome =====

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

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%
((Gandhi D, Chen J, Pearl M, Huang J, Gemmete JJ, Kathuria S. Intracranial dural
arteriovenous fistulas: classification, imaging findings, and treatment. AJNR Am 
J Neuroradiol. 2012 Jun;33(6):1007-13. doi: 10.3174/ajnr.A2798. Epub 2012 Jan 12.
Review. PubMed PMID: 22241393.
)).