An arteriovenous malformation (AVM or angioma) is a congenital malformation of the blood vessels and functions like a short circuit between a cranial artery and a cranial vein. The blood flow is increased in the AVM and the walls of the vessels of the AVM are thinner, which results in the risk of a cranial haemorrhage. Patients with an AVM have a risk of haemorrhaging of approximately 4% per year. Symptoms such as epilepsy can occur even if there is no bleeding. In order to prevent (additional) bleeding, the AVM is either surgically removed or collapsed or blocked (embolisation) with the aid of a catheter. If this is not completed successfully or if the treatment risk associated with such a procedure is too great, there is no option to irradiate the AVM using the Gamma Knife . Patients may also be treated with combinations of these three procedures.
If the AVM has been completely remedied after an operation, or is fully blocked after embolisation, there is no longer any risk of bleeding. Following radiosurgical treatment, it can take up to 4 years for the AVM to close off completely. During this time, there is a residual risk of cranial haemorrhage. The probability of complete obliteration (closure of the AVM) after Gamma Knife treatment is around 70% after 2 years and 80%.after 3 years. It is still possible for an AVM to close in the fourth year.
The risk of side-effects is approximately 2-3% and depends on the dose of radiation, the total volume of radiation and the localisation of the AVM.