An arteriovenous malformation (AVM) is an unusual formation of arteries and veins which are congenital in origin and occur throughout the body. When they occur within the brain they may cause symptoms such as seizure, headache or progressive neurological deficits. Most importantly they can spontaneously bleed resulting in a stroke with lasting neurological problems or even death.
An AVM may have several forms, such as a direct connection between an artery and vein, an AV fistula. Unusual formations of veins which bleed and cause seizures are cavernous angiomas. Abnormalities of very small vessels are capillary angiomas. The most important (and dangerous) are AVM’s which have both arterial and venous components. These AVM’s have a 3 to 4 percent chance of spontaneous hemorrhage each year. Roughly 10 percent of the hemorrhages will be fatal and about 15 percent of victims will suffer a continuing neurological deficit, such as weakness, sensory or visual loss, speech abnormality, etc.
Surgical excision of the AVM brings an immediate cure, but not all AVM’s can safely be removed. Gamma Knife radiosurgery can play a role in the obliteration of smaller AVM’s. This technique has the advantage that is non-invasive and accomplished in a single session. The disadvantage is that the effects of focused radiation occur over months and years, during which time the patient is still at risk for spontaneous hemorrhage. In general, AVM’s under 1 cm in diameter have a 90 percent chance of obliteration, while those under 2 cm have an 80 percent change of cure. Only about 50 percent of malformations 3 cm in size are obliterated.