An arteriovenous fistula forms where an abnormal connection develops between arteries and veins. Unlike an arteriovenous malformation there is no nidus (Click here for an explanation of these terms) and the blood vessels are in direct contact. This may develop in the substance of the brain itself (pial fistula) or within the leathery lining of the brain and spinal cord, the dura (dural fistula). Additional information on spinal vascular malformations is available here.


Dural Arteriovenous Fistulae (DAVF)

Dural fistulae develop within the brains covering. They may involve arteries delivering blood to the brain but they may alsorecruit blood supply from the arteries of the scalp. The arteries supply blood directly into the large veins within the dura called sinuses. However the veins of the brain do also normally drain into these sinuses and there are occasionally DAVFs which allow blood to find its way back into the cortical veins. These subtypes of DAVF pose significant risks of bleeding and merit more proactive management. When the blood flow is confined within the lining of the brain the DAVF may not requie any treatment.

DAVF may develop in repsonse to clot forming in veins of the head an neck. This itself may be the result of trauma or infection.The symptoms which a DAVF may produce can be uncomfortable and even if there is little risk of stroke treatment may be sought to relieve them, The symptoms vary according to the location of the fistula and include:

Pulsatile Tinnitus: A noise in the ear which waxes and wanes with the heartbeat. Typically this is assosciated with a fistula into a large venous sinus just behind the ear called the transverse sinus. This may be uncomfortable, disturb sleep and impair hearing. For some it is less severe and is not intrusive or disabling.

Headache: may result from congestion of the veins inside the head and a resultant increase in pressure within.

Visual and Ocular Symptoms:The large carotid artery in the neck passes throught the bone at the base of the skull to enter the brain. As it does so the artery is surrounded by a large lake of venous blood contained within the skull base and called the cavernous sinus. Fistulae may form between this artery and the cavernous sinus as a result of infection, trauma or rupture of aneurysms of the carotid. These are termed carotico-cavernous fistulas (CCF)


Cortical Pial Fistulae

Pial fistulae have been recognised as distinct clinical entities relatively recently. They form between the arteries and veins within the substance of the cerebral cortex. They pose similar potential problems to brain AVMs. It requires a digital subtraction angiogram to distinguish between the two. Cases of pial fistula have been reported as developing following blockage of veins in the brain. The have also been assosciated with genetic mutations e.g in the the RASA1 gene when seen as part of the Capillary Malformation-AVM (CM-AVM). For more information about CM-AVM please see here in our section on brain AVM.

The particular concern in relation to pial AVF is brain haemorrhage. There is little data to tell us the how common they are in the healthy population but they are presently generally thought of as having relatively high risk of brain haemorrhage compared to brain AVM. These lesions may be treated in the same way as other vascular malformations of the brain. They may be more ameanable to cure by endovascular treatment than other forms of pial arteriovenous malformation.