Cranial dural arteriovenous shunts. Part 3. Classification based on the leptomeningeal venous drainage.

The commonly used Borden and Cognard classification systems for the prediction of clinical behavior of cranial dural arteriovenous shunts focus on the venous drainage, particularly the presence of leptomeningeal venous drainage, and on the direction of flow, particularly the presence of retrograde flow. In addition, the latter includes ectasia and spinal drainage as criteria of two distinct grades. However, none of the above classifications (a) differentiates direct from exclusive leptomeningeal venous drainage, (b) considers cortical venous congestion as a factor potentially associated with an aggressive clinical course, and (c) anticipates ectasia in shunts with a mixed dural-cortical venous drainage (type 2). In this study, we analyzed the angiographic images of 107 consecutive patients having a cranial dural arteriovenous fistula with leptomeningeal venous drainage, based on a newly developed scheme. This scheme, symbolized with the acronym "DES," groups the dural shunts according to three factors: directness and exclusivity of leptomeningeal venous drainage and signs of venous strain. According to the combination of the three factors, eight different groups were distinguished. All analyzed cases could be assigned to one of these groups. Directness of leptomeningeal venous drainage expresses the exact site of the shunt (bridging vein vs sinus wall), whereas exclusivity expresses venous outlet restrictions. All bridging vein shunts had a direct leptomeningeal venous drainage. Almost all bridging vein shunts and all "isolated" sinus shunts had an exclusive leptomeningeal venous drainage. Venous strain, manifested as ectasia and/or congestion, denotes the decompensation of the cerebral venous system due to the shunt reflux. The comparison of the presented concept with the currently used classifications highlighted the advantages of the former and the weaknesses of the latter.