Arteriovenous Malformation – Angioma
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 for haemorrhage of approximately 4% per year. Yet symptoms such as epilepsy can still 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 completely successful or if the risk associated with such a procedure is too great, there is the option of irradiating 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 more risk of haemorrhage. Following radiosurgical treatment, it can take up to four 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) after Gamma Knife treatment is around 70% after two years, and 80% after three years. It is still possible for the AVM to close in the fourth year.
The risk for side-effects is roughly 2 to 3% and depends on the dose of radiation, the total volume of radiation and the localisation of the AVM.
