This nonsurgical procedure is used to treat an arteriovenous malformation (also called an AVM) located deep inside the brain. During this procedure, beams of radiation are precisely focused at the AVM, destroying the abnormal vessels while leaving surrounding tissue unharmed. The procedure may take several hours.
Children may be given general anesthesia to keep them from moving during the procedure, but adults are usually lightly sedated and kept awake. The patient’s scalp is numbed, and a stereotactic frame is secured to the head with pins tightened a few millimeters into the scalp and into the skull bone. The stereotactic frame provides a precise coordinate system to localize the target in the brain and spare the surrounding normal tissue.
The patient is placed in an MRI machine. The brain is scanned to produce a three-dimensional map of the AVM. Reference points on the frame will allow the physician to accurately target the AVM while avoiding healthy parts of the brain. The patient is then taken to the interventional radiology suite, and a cerebral angiogram is performed with the stereotactic frame in place.
Planning the Procedure
Using the MRI and angiogram, the physician creates a highly customized treatment plan that will deliver a focused dose of radiation that tightly conforms to the irregular three dimensional outline of the AVM. This planning process usually takes a few hours to complete.
The patient is put inside the machine that delivers the radiosurgery. This may be called a “Gamma Knife”, a “LINAC”, or a “Cyberknife.” The machine bombards the AVM with beams of radiation from many angles. Each beam is too weak to cause damage by itself, but the beams’ combined power injures the vessels at the selected target site.
End of Procedure
The head frame is removed. Most patients are discharged home the same day. The four pin holes on the scalp may be a bit sore, and the patient may have a headache or feel nausea. Swelling in the eyelids commonly occurs in the first several days after the procedure, and numbness in the back of the scalp that may last for several weeks may also occur. There is also an increased risk of a seizure in the initial weeks following the radiosurgery.
Most AVMs require just the one dose of radiation in a single day, but some larger AVMs may be treated in two or three sessions, each separated by several months. Within two to three years of treatment, the focused radiation causes the arteries of the AVM to close. Until the AVM completely closes, the patient is still at risk for hemorrhage. Some AVMs may be found to have not completely obliterated 3 years after radiosurgery. In such cases, a second session of radiosurgery or craniotomy to remove the (usually much smaller) residual AVM may be necessary. Follow up imaging is therefore necessary and typically is done on a surveillance basis with MRI every six months. After 2-3 years, a conventional angiogram is also usually performed to confirm obliteration.