Several classification systems have been described to characterize DAVFs, with Borden and Cognard systems being the most commonly utilized contemporary grading schemes.
Cortical venous drainage is the defining angiographic feature that distinguishes benign (low-grade) from aggressive (high-grade) fistulas.
Borden I, Cognard I, and Cognard IIa are considered low-grade, while all others are high-grade.
The two most common classifications for dural AVFs are the Borden and the Cognard classification shown below:
Borden Classification
Type
Features
I
DAVF drainage into a dural venous sinus or meningeal veins, with normal anterograde flow.
Usually clinically benign.
II
DAVF draining anterograde into dural venous sinus, but with retrograde flow into cortical veins.
III
DAVF with direct retrograde flow from fistula into cortical veins, causing venous hypertension.
Cognard Classification
Venous drainage
Type
Features
Course
Sinus
I
Normal antegrade flow into a dural venous sinus
Benign course
IIa
Drainage into a sinus with retrograde flow within the sinus
Sinus reflux caused IC-HTN in 20%
IIb
Drainage into a sinus with retrograde flow into cortical vein(s)
Reflux into veins induced hemorrhage in 10%
IIa + b
Drainage into a sinus with retrograde flow within the sinus and cortical vein(s)
Aggressive in 66% with bleeding and/or IC-HTN
Cortical veins
III
Direct drainage into a cortical vein without venous ectasia
Hemorrhage occurs in 40%
IV
Direct drainage into a cortical vein with venous ectasia
Hemorrhage occurs in 65%
Spinal
V
Direct drainage into spinal perimedullary veins in addition to all of the above
Progressive myelopathy in 50%
Presence of cortical venous drainage is the most important determinant of rupture nsk from dural arteriovenous fistula.
The other factors listed have not been convincingly linked to risk of hemorrhage.
