Dural arteriovenous fistula (DAVF)

Created 21/04/2021, last revision 12/11/2023

dural arteriovenous fistula (DAVF) is characterized by abnormal connections (shunts) between an artery and a vein; DAVF typically presents with tinnitus, hemorrhage, or venous hypertension
DAVF accounts for ∼ 10-15% of vascular malformations and most commonly affects patients aged 40-60 years
most DAVFs are idiopathic; some patients have a history of previous craniotomy, head trauma, or dural sinus thrombosis [Gandhi, 2012]

Pathology

*Borden* [Borden, 1995]
Type I – anterograde drainage directly into dural venous sinuses/meningeal veins Ia – 1 feeding artery Ib – >1 feeding arteries
Type II – anterograde drainage into dural sinuses/meningeal veins + retrograde drainage into subarachnoid veins
Type III – predominantly retrograde drainage into cortical veins with their dilatation, no dural sinus or meningeal venous drainage

*Cognard* [Cognard, 1995] This classification provides valuable data for the determination of the risk with each dural AV fistula and enables decision-making about the appropriate therapy
Type I – only anterograde drain into dural sinuses, benign course
Type II IIa – simultaneous retrograde drainage into the dural sinus (intracranial hypertension in 20% of cases) IIb – simultaneous retrograde drainage into cortical veins (bleeding in 10%) IIa+b – simultaneous retrograde drainage into dural sinus + cortical veins
Type III, IV, V – no dural sinus drainage (high risk of bleeding – 40-65%) III – direct cortical venous drainage without venous ectasia IV – direct cortical venous drainage with venous ectasia V – spinal venous drainage (⇒ high risk of progressive myelopathy)

Clinical presentation is variable and depends on the location of the fistula and the pattern of venous drainage

pulsatile tinnitus (typically with sigmoid and transverse sinus drainage)
symptoms of venous hypertension/congestion
- headache
- hemorrhagic venous infarction
- spinal myelomalacia
- cranial nerve palsies
- ocular (orbital) symptoms – conjunctival chemosis and swelling (carotid-cavernous fistula) – DDx of cavernous sinus thrombosis!
- intracerebral or subarachnoid hemorrhage (high risk, especially in type II and III) [Li, 2015]
  - type II and III have an annual risk of ~8% [Gandhi, 2012]
DAVF can be high-flow and consume a significant portion of ejection fraction (EF) => exertional dyspnea, left ventricular hypertrophy (LVH)

CT/MRI
- more useful for detecting complications (hemorrhage, venous infarction, edema)
- insufficient for diagnosing DAVF – vascular imaging must be added (however, enlarged arterial feeders or dilated pial vessels in the subarachnoid space may sometimes be seen)
vascular imaging (CTA/MRA or DSA)
- often, multiple feeders are present without an intervening nidus
- dural sinuses are filled with contrast during the arterial phase
- dilated and tortuous cortical veins in the subarachnoid space
- DSA remains the best method to accurately assess feeding vessels and the presence and extent of retrograde venous drainage
neurosonology
- Doppler shows decreased resistance (RI< 0.45) and increased flow velocity

treatment decision is based on the following:
- type of the fistula
- patient’s age and comorbidities
- presence of symptoms attributable to the fistula

usually recommended for Borden I, Cognard I-IIa
in mild cases, intermittent external compression of the feeding artery may be helpful (retroauricular compression in DAVF fed by the occipital artery)

an indisputable indication is for DAVF Borden types II and III or Cognard IIb-V due to the high risk of bleeding (an annual risk is ~8%)
type I with severe tinnitus may also be indicated for endovascular treatment

transarterial approach (TAE) – super-selective distal catheterization
- e.g., using Onyx [Lv, 2009]
transvenous approach (TVE) – mainly in cases with multiple small feeding arteries unsuitable for embolization
combined approach (TAE + TVE)

indicated if endovascular treatment is not possible or has been unsuccessful or only partially successful