An arteriovenous fistula is an abnormal connection (or shunt) of an artery directly to veins in tissues around the brain, spinal cord, or venous spaces called sinuses. AVF are acquired lesions and not congenital as is thought of AVM (arteriovenous malformations).
They can form at any age but are more common in women over the age of 50. AFV's usually present with pulse synchronic bruits (heartbeat sound from the ears), headaches or signs of raised intracranial pressure often resulting in papilledema. Often patients suffer from these bruits in the ear and this explains the flow of arterial blood into the Transverse and Sigmoid sinuses.
They can also show intracranial haemorrhaging and intracranial hypertension.
Normally oxygenated arterial blood is pumped to the tissues via capillaries and then deoxygenated
blood and waste is discharged through the venous pathway. In AVF the direct arterial and venous
connection deprive the tissue or body parts of oxygen. Also, high-pressure arterial blood is pumped
into the veins and venous sinuses and this can lead to serious complications.
The raised intracranial pressure, in my case, was not due to vein thrombosis but due to the decrease in absorption of the cerebrospinal fluid (CSF) by the compromised venous system.
There are 2 types of AVF –
1. Dural AVF’S – when a fistula forms within a fibrous tissue covering the brain called the Dura.
Here the high pressure arterial blood drains directly into the Dural sinuses and if there is an
obstruction or narrowing of the sinuses then the high-pressure blood is directed to the
cerebral veins. The consequence of this being increased intracranial pressure which can lead
to seizures, headaches, papilloedema as well as nerve palsy.
2. Carotid-Cavernous Fistula – When a fistula forms between the carotid artery and a large
venous lake called the cavernous sinus. These are commonly single shunt and very rarely
several transdural feeders and happen when the carotid artery passes through the
cavernous sinus. Consequences of carotid-cavernous fistula are proptosis, ophthalmoplegia
and vision loss.
Most AVF’s form with no precipitating events but a few are related to previous infection, traumatic
injuries, sinus occlusion or chronic venous hypertension. Dural AVF’s can present with a bruit
(rumbling noise) in one ear that follows a heartbeat. Most Dural AVF’S are benign but in some
instances it can result in life-threatening haemorrhages and venous hypertension. Majority of Dural
AVF does involve the left-side transverse and sigmoid sinus.
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