Arteriovenous malformation radiosurgery: a twenty year perspective.

Arteriovenous malformations (AVMs) are congenital anomalies of the cerebrovasculature with poorly formed blood vessels that shunt blood directly from the arterial circulation to the venous system bypassing the capillary network. The high pressures and flow rates in AVM vessels combined with poor construction of the abnormal shunting vessel walls make them prone to rupture and intracranial hemorrhage. In some patients, they are associated with aneurysms and other vascular abnormalities. The risks and benefits of AVM management must be weighed carefully in each patient. Once identified, AVMs may be suitable for one or more of four management strategies alone or in combination:13 observation, endovascular embolization, surgical excision, or stereotactic radiosurgery. A number of factors are considered in making a recommendation. These factors include the patient’s age, the patient’s medical condition, bleeding history, prior management, volume of AVM, location of AVM, presenting symptoms, AVM architecture (compact versus diffuse), “operability” estimate, presence of an aneurysm, and prior experience or training. A broad management algorithm is shown in (Figure 13.1). Optimal management depends on the estimated risk of subsequent hemorrhage, which is influenced by the flow and location features as well as symptoms in each individual patient. Younger age, prior hemorrhage, small AVM size, deep venous drainage, and high flow may make subsequent hemorrhage more likely. Observation may be most appropriate for large-volume AVMs (average diameter 4–5 cm), especially for patients who have never bled.25 Endovascular embolization is often used as an adjunct to surgical removal of the AVM through craniotomy and at times before stereotactic radiosurgery.38,61 Embolization before radiosurgery is thought by some to be beneficial but may lead to less reliable recognition of the target volume suitable for radiosurgery. Recanalization of embolized AVM components may require subsequent retreatment for portions of the AVM previously thought to be occluded by successful embolization. Surgical removal is an important option for patients with resectable AVMs, although incomplete surgical removal may require eventual radiosurgery. Although the size of the AVM, pattern of venous drainage, and neurological eloquence of adjacent brain are important considerations for prediction of outcome after resection,69 outcome after AVM radiosurgery can be predicted using nidus volume and location and age of the patient.53 Radiosurgery is a minimal access option for patients with intracranial AVM. The chief benefit of radiosurgery is to eliminate the threat of spontaneous intracranial hemorrhage by gradual obliteration of the AVM nidus over 2 to 3 years.39,57