Sunday 11 September 2011

Dural Arteriovenous Fistula (Dural AVF) MRI

A 28 y o female with right orbital proptosis and congestion.
MRI Brain Axial T2w images
This MRI study shows abnormal serpigenous T2 flow voids along tentorium and cerebral convexity dura, at incisura suggestive of Dural AV Fistula.
An associated abnormal dilatation of right side superior ophthalmic vein and orbital proptosis.
Superior sagittal sinus show normal T2 flow voids but abnormally smaller in caliber.

Dural AV Fistula

A rare abnormal connectivity between arteries and veins, lies exclusively along dural covering of the brain or spinal cord and referred accordingly as a Cranial and Spinal Dural AVF.

Cranial DAVF is supplied by branches of the carotid artery (external and internal carotid arteries) and possibly also by branches of the vertebral artery before these arteries penetrate the dura.
The fistulous communications seen as serpigenous dilated vessels with T2 flow voids along dura overlying cererebral convexity and along tentorium. Frequently the blood flow in a DAVF is very high, and it may cause blood to flow in the opposite direction of normal over the brain's surface.

Commonly diagnosed in women over the age of 40 years. Unlike AVMs, which are thought to be present from birth, cranial DAVF most often develop later in life following hypoplasia or chronic thrombosis of dural venous sinuses particularly superior sagittal sinus.

Cranial DAVF may present with pulsatile tinnitus or pulsatile proptosis, impairment of vision and eye movement, isolated but persistent or progressive headache; hemorrhage
Unfortunately, the diagnosis may be missed or delayed because such lesions occur so rarely, CT may be normal and even in case of MRI, a common practice of inadequate sequences particularly screening protocols may miss the diagnosis.

Pathogenesis of Dural AV Fistula
Dural AV fistula are shunts between the meningeal arterial networks and the dural venous sinuses. Long standing dural sinus thrombosis result in obstruction in venous outflow which raises intra cranial venous sinus pressure. This venous hypertension leads to ischemia, followed by aberrant angiogenic activity along the Dura. CVT here is the primary event that result in venous hypertension and fistula. Sinus thrombosis may be the primary even as result of turbulent flow in the Dural venous sinuses secondary to DAVFs.

Highly challenging, various line of management and materials are under debates.
Intrasinus stenting can relieve raised venous sinus pressure but may increase arteriovenous pressure gradient and shunt flow.
Arterial embolization of DAVF, without correction of venous hypertension can give rise to another fistula.
Intermittent carotid arterial compression.
Percutaneous intra arterial embolization using detachable balloons, isobutylcyanoacrylate, or polyvinyl alcohol particles.
Transvenous embolization with coils or liquid adhesives.
Surgical venous bypass using saphenous vein.
Gamma knife stereotactic surgery.

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