Arteriovenous Malformations
Features and treatment of these abnormal blood vessel structures
Arteriovenous malformations in the spine or brain can give rise to a number of neurological signs and symptoms
Arteriovenous malformations are abnormal blood vessels occurring in the brain and spine and other parts of the body. It is brain and spine AVMs that present the greatest challenge. The abnormality is the absence of capillaries between a vein and an artery. It is this lack of capillary network that produces most of the problems associated with AVMs . Capillaries form a buffer between arteries and veins, slowing down blood flow and helping to keep pressures in the larger vessels at correct levels.
The cause is thought to be developmental, occurring just before or just after birth. They are diagnosed by CT scan.
Symptoms of AVMs
A number of people are asymptomatic, the AVM only being found on scanning for some other condition.
When situated in the spine the features may be intermittent bouts of numbness and or tingling in the limbs, back pain and sometimes headaches. Unsurprisingly AVMs in the brain often manifest in more varied ways.
- Headache: a frequent symptom, probably due to pressure effects from the abnormal blood vessels.
- Migraine: people with AVMs seem to be more prone to migraines than others.
- Seizures: the nature of the epilepsy depends on which part of the brain the AVM is situated. If in an area that controls movement, generalised clonic/tonic seizures may occur. Sometimes partial seizures occur with perhaps just a limb subject to the seizure. If the AVM is in part of the brain involved with emotions then temporal lobe seizures may result. These do not result in uncontrolled movement but inappropriate emotions or hallucinations of smells or sounds.
Complications
The chief complication is haemorrhage. Due to pressure effects, AVMs are prone to bleed. This can of course be serious, particularly so in brain AVMs, since the damage caused will be the same as for stroke with results varying from mild to catastrophic. Fortunately the product of an AVM bleed is often mild and transient. This may be because when AVMs do bleed it is often at low pressure resulting in less blood loss and therefore less brain damage.
Because of the abnormal blood flow through AVMs blood can pass through nearby areas of the brain too quickly, not allowing enough time to fully oxygenate the tissue. This is known as the ‘steal effect’. It can, in time, lead to progressive neurological deficit: loss of memory or loss of intellect for example.
It should be stressed that all this is not inevitable in AVM sufferers – many lead long and relatively healthy lives
Treatment
Symptoms such headaches, migraines and seizures are usually treated with medication.
Spinal AVMs are mostly treated by surgical removal, this is either relatively easy or difficult depending the exact site of the lesion.
Brain AVMs are more difficult. Small lesions can be removed surgically if easy to get to without causing too much collateral damage.
Large AVMs and those in tricky areas of the brain are usually treated (if treated at all) initially by embolisation. This involves passing a catheter from the groin, through the femoral artery and aorta into the vessels of the brain (guided by scan). When the AVM is reached a drop of superglue is used to seal off one of the feeding vessels. The process is repeated until all the feeding vessels are blocked. Over the following months the AVM shrinks until it is small enough to be obliterated by guided radiation.
This article is for information only. If you have any concerns regarding your health, you should consult you doctor.
References
An Introduction to Neurosurgery by Jennett and Lindsay. Butterworth-Heinemann 1994
National Institute of Neurological Disorders and Stroke
