Dural arteriovenous fistula (DAVF)

Definition

• Acquired pathologic connections b/w dural art. and dural venous sinuses, meningeal veins, or cortical veins.

Epidemiology

• DAVFs account <10% of all Cerebral Vascular Malformations.
• In US & Europe - majority involve the transverse sinus or sigmoid sinus
  • Japan - cavernous sinus MC

Etiology

• Idiopathic (MC), but have been assoc. w/ venous sinus thrombosis, meningitis, sinus infx, Qx, hypercoagulable states, trauma.

Pathogenesis

• venous sinus thrombosis → venous congestion & hypertension → upstream dilation of capillaries → arteriovenous shunting.
• venous hypertension → ↓ perfusion → ↑ expression of vEGF → ↑ angiogenesis.

Pathology

• Lack a nidus on angiography.

DAVF Classification

• 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.

Borden classification has three types (Type I, II, and III), which can be remembered as "One, Two, Three". Each type's key feature can be remembered by the mnemonic: "Dura, Sinus, Brain"

• Type I (Dura) - DAVF drains directly into dural venous sinus, with antegrade flow. It's a benign type, associated with lower risk.
• Type II (Sinus) - DAVF drains into dural venous sinus, with reflux into the sinus. It's an intermediate type.
• Type III (Brain) - DAVF drains retrogradely into cortical veins. It's a malignant type, associated with higher risk.

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.
• In the Cognard system, the pattern of venous drainage is the most critical factor.
• Lesions with retrograde flow in the cortical veins (IIb, IIa+b, III & IV) are considered high risk for bleeding or intracranial hypertension.

The Cognard Classification is more detailed, with five types (Type I, IIa, IIb, IIa+IIb, III, IV, and V). For Cognard, the mnemonic could be "Drain, Sinus, Brain, Both, Exhaust, Flow, Vein":

• Type I (Drain) - DAVF drains into venous sinus with antegrade flow
• Type IIa (Sinus) - DAVF drains into venous sinus with reflux
• Type IIb (Brain) - DAVF drains into cortical vein
• Type IIa+IIb (Both) - DAVF drains into sinus with reflux and cortical vein
• Type III (Exhaust) - DAVF drains directly into cortical vein without venous ectasia
• Type IV (Flow) - DAVF drains into cortical vein with venous ectasia
• Type V (Vein) - DAVF drains into spinal perimedullary veins.

Presentation

Sign/Symptom	No. (%)
Pulsatile tinnitus	25 (92%)
Occipital bruit	24 (89%)
Headache	11 (41%)
Visual impairment	9 (33%)
Papilledema	7 (26%)

Management of DAVF