There has been considerable controversy regarding the best mode of treatment: surgical excision, stereotactic radiosurgery, endovascular embolization (or a combination of these), or no treatment. The complexity of these choices is discussed in the review by Solomon and Connolly. The only adequate randomized trial, ARUBA, reported by Mohr and colleagues (2014), comparing intervention of any kind to expectant management found that death or stroke occurred in 10 percent in the expectant management group compared to 31 percent in the group that had intervention. The main criticisms have been the short follow up of 33 months and the lack of assignment by risk of rebleeding or suitability for surgery or another type of treatment. This has engendered considerable controversy and criticism but must be taken into account when advising patients. In a meta-analysis of 13,698 patients, approximately 7 percent with surgical resection and 5 percent after stereotactic radiosurgery were left with neurological deficits (van Beijnum et al).
The Spetzler-Martin Scale, which uses a point scale for size (1 to 3), location (eloquent vs non-eloquent) and venous drainage (deep vs superficial) has been used to give guidance as to the surgical difficulty and surgical risk. Grades IV and V, generally representing large deep lesions, are generally not resected; grade III lesions, typically mid or large sized lesions, may be approached surgically but often with preceding interventional embolization of parts of the lesion. Some 20 to 40 percent of AVMs are amenable to block dissection, with an operative mortality rate of 2 to 5 percent and a morbidity of 5 to 10 percent. For inaccessible lesions, attempts have been made to obliterate the malformed vessels by ligation of feeding arteries or by the use of endovascular embolization with liquid adhesives or particulate material that is injected via a balloon catheter that has been navigated into a feeding vessel. Complete obliteration of large AVMs is usually not possible by these methods but they are effective in reducing the size of the AVM prior to surgery.
Several modes of radiosurgery are used to decrease the size of the lesion, albeit with a substantial delay. This approach is utilized most often with AVMs of 3 cm or smaller located in an area of the brain in which resection would be likely to produce a serious neurologic disability. Kjellberg and Chapman pioneered the treatment of AVMs using a single dose of subnecrotizing stereotactically directed proton radiation. The technique of stereotactic radiosurgery has been adopted using photon radiation sources, such as a linear accelerator, gamma radiation (Karlsson et al) and other modes of focused x-ray radiation as accepted alternatives to operative treatment of small lesions or those situated in deep regions, including the brainstem, the thalamus, or in “eloquent” areas of the cortex. The main drawback to radiosurgery is that obliteration of AVMs occurs in a delayed manner, usually with a latency of at least 18 to 24 months after treatment, during which the patient is unprotected from rebleeding. The likelihood of successful radiotherapy treatment and the nature of the risks depend on the location and size of the AVM and the radiation dose delivered. After 2 years, 75 to 80 percent of AVMs smaller than 2.5 cm in diameter have been obliterated. Even for those AVMs that have not been totally eliminated, the radiation effect appears to confer some long-term protection from bleeding. Of the larger ones, a majority shrink or appear less dense. A proportion of larger AVMs that are initially obliterated will later recanalize, and many of these will subsequently bleed. Among more than 250 patients whose AVMs disappeared following proton-beam therapy, there has been no recurrence of hemorrhage for up to 10 years (Chapman, personal communication). The results of treatment with focused radiation have been about the same. In one study, the risk of hemorrhage was reduced by 54 percent between the time of radiation and obliteration of the malformation and by 88 percent thereafter (Maruyama et al).