A dural arteriovenous fistula (DAVF) is a collective term given to a heterogeneous group of conditions that share arteriovenous shunts from dural vessels. They make ~ 10 – 15% of all AV shunting cerebral vascular malformations.
They typically have multiple feeders and are usually acquired, most frequently from as a result of neovascularisation induced by previously thrombosed dural venous sinus (typically transverse sinus). Therefore supply is typically from the same branches that supply meningeal arterial supply.
- supratentorial : middle meningeal artery (ECA)
- anterior cranial fossa : ethmoidal branches of the ophthalmic artery (from ICA)
- cavernous sinus : dural branches from the ICA and accessory meningeal branch of the maxillary artery (via foramen ovale) – branch of ECA.
- posterior cranial fossa : dural branches from the vertebral arteries, branches from occipital and ascending pharyngeal arteries.
Clinical presentation is highly variable and depends on the location of the supplying and draining vessels, as well as the presence of complications (see below).
- cranial nerve palsies
- orbital symptoms (see caroticocavernous fistula)
- symptoms of venous hypertension
- raised intracranial pressure
- focal neurological deficits
- transverse / sigmoid sinus
- most common
- least likely to have retrograde venous drainage
- cavernous sinus (indirect caroticocavernous fistula)
- superior sagittal sinus
- straight sinus
- other venous sinuses
- anterior cranial fossa
- typically only ICA supply due to meningeal supply of this region
- frequently associated with retrograde venous drainage
- tentorium : frequently associated with retrograde venous drainage
Likelihood depends on venous drainage, not arterial supply (see below), and this in turn correlates with location.
- subdural haemorrhage (SDH)
- intracranial haemorrhage (ICH)
- subarachnoid haemorrhage (SAH)
- intracranial hypertension
- venous congestion and oedema
- spinal myelomalacia
Venous drainage pattern correlates with increasingly aggressive neurological clinical course.
- type I : confined to sinus wall, typically after thrombosis.
- type II
- Ia : confined to sinus with reflux (retrograde) into sinus but not cortical veins
- IIb : 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)
- type V : spinal perimedullary venous drainage, associated with progressive myelopathy
Diagnosis can be difficult on non-contrast CT, but should be thought of when an intracranial haemorrhage (SAH or ICH) is in an unusual location or age group.
With contrast and CTA abnormally enlarged and tortuous vessels may be evident in the subarachnoid space, corresponding to dilated cortical vein.
An enlarged ECA or enlarged transdiploeic vessels may also be a clue.
Abnormal dural venous sinuses should be sought.
Again, the diagnosis is difficult in patients without retrograde venous drainage, with dilated pial vessels in the subarachnoid space being a potential clue.
In patients with retrograde leptomeningeal venous drainage oedema is present in approximately half of patients, although it may also be seen in patients who do not have retrograde drainage on angiography.
The regions of white matter oedema may also enhance. These findings are indicative of an aggressive fistula with a high rate of haemorrhage.
DSA remains the gold standard in both diagnosis and accurate classification of dAVF, allowing not only systematic evaluation of feeding vessels (and thus planning for potential intervention) but also demonstrating the presence and extent of retrograde venous drainage.
- conservative (especially type I)
- higher grades
The grade of the dural arteriovenous fistula and a patient’s symptoms factor into the treatment strategy. Typically, Borden grade I lesions can be followed without treatment unless the associated symptoms affect a patient’s quality of life significantly. In that case, stereotactic radiosurgery may be considered. Endovascular treatment, possibly combined with microsurgical treatment, is usually recommended for grade II and III dAVFs, which have an increased risk of hemorrhage.
At Barrow, the usual treatment paradigm includes a thorough catheter-based angiographic evaluation with possible endovascular intervention during the same setting. Endovascular surgery involves both transarterial and transvenous approaches to the site of the fistulous connection. Typically, large feeding arteries are embolized transarterially to reduce blood flow through the fistula. Then transvenous routes to the fistula can permit coil embolization of the fistulous point. Sometimes, transarterial routes are large enough to permit glue embolization of the fistula as well. If the fistula cannot be obliterated by endovascular methods alone, embolization is followed by microsurgical obliteration. Postoperative angiography is used to confirm successful obliteration.