Encyclopædia Neurochirurgica
Brain arteriovenous malformation
4.3.1. Staged Volume radiosurgery
Consists of dividing the AVM into equal volumetric portions and treating each one as a different radiosurgical section, with intervals of 6 to 9 months between staged treatments. Some authors advocate that the basal portions must be treated before more superficial portions, the most medial portion before more lateral portions and portions of the AVM filled in carotid before portions filled in vertebral artery angiography. [3, 11] Major draining veins should be irradiated last to minimize the risk of obstruction of venous outflow.
Staged radiosurgery is a viable and relatively safe treatment for large AVMs, in otherwise untreatable patients. [3, 11, 86, 91] Chung et al. [11] in a series of six patients (volumes treated ranged from 47 to 72 cm3) with a mean total follow-up of 28 months (range from 15 to 54) total obliteration was reported in 33.3% and incomplete obliteration 66.7%; no patient developed radiation-related clinically complications. Amponsah et al. [3] in a series of five patients (volumes treated ranged from 22 to 50 cm3) with a mean total follow-up of 81.2 months (range from 42 to 120 months) reported total obliteration in 40%, 40% near total obliteration and 20% poor obliteration; radiation-related mild complication were observed in 40% of patients.
4.3.2. Hypofractionated stereotactic radiotherapy (HFSRT)
It should be offered only to patients with AVMs unsuitable to surgery or single fraction procedure because of relatively low probability of obliteration after the fractionated irradiation. It still remains an attractive option for patients with otherwise untreatable AVMs that present repeated hemorrhage, progressive neurological deficits, intractable seizures, and other severe symptoms. [105]
The AVM is completely irradiated in multiple sections (3 to 6) with low dose (4 to 7 Gy, the total doses usually ranged from 28 to 42 Gy). [9, 105] However, the results are below expectation if compared with the results of stereotactic radiosurgery for selected, small lesions. The treatment protocols, radiotherapy devices, mean AVM size and characteristics, and follow up are very heterogeneous in literature, and so are the rates of obliteration and complications. Blamek et al. [9] reported a rate of total obliterated of only 21% and an additional 34% of partial obliterations after three years of follow-up. Xiao et al. [110] reported no lesion obliterated, however, they observed a significant decrease in the volume of patent AVMs and propose that this may turn some of these AVMs into manageable lesions with a single-dose of SRS or microsurgery. Lindvall et al. [51] observed better results, with obliteration rates of 56% and 81% for lesions of volume 4-10 cm3 and from 50% to 70% for lesions larger than 10 cm3 after two and five years of follow-up, respectively.
The complication rate varies in literature from low rates of radiological changes and mild symptoms to 86% radiographic changes and 28% symptomatic. [104, 105]
In the first years after treatment, the annual risk of bleeding is about 2% (similar to no treated patient). The HFSRT does not increase the risk of subsequent hemorrhage. [9, 110]