Hanakita S, Koga T, Shin M, Igaki H, and Saito N. Application of Single-Stage Stereotactic Radiosurgery for Cerebral Arteriovenous Malformations >10 cm3. Stroke. 2014
Arteriovenous malformations, commonly referred to as AVMs, represents one type of non-neoplastic vascular structure that has been quoted to affect 0.14% of the population. While this percentage may seem small, these congenital lesion can have a lifelong risk of bleeding as high as 4% and tend to enlarge with age as they progress from a relatively low flow state in youth to one of high pressure in adulthood. It has been estimated that hemorrhage at presentation occurs in an average of 50%. Hanakita et al in their study probe the important question surrounding the proper treatment of larger AVMs. Stereotactic radiosurgery (SRS) has been accepted as one form of treatment but has historically targeted small (usually less than 3cm maximum diameter) or deep AVMs. Larger lesions have remained difficult to treat as SRS is limited by irradiation dose and larger diameter is directly related to an increased complication rate during direct excision.
This study sought to retrospectively examine rates of obliteration, hemorrhage after treatment and adverse events in 65 patients with AVMs >10cm3 who underwent single stage SRS. The authors cite literature in their introduction that staged SRS has had limited treatment effects with a high adverse event rate. They propose that larger lesions may be amenable to a single stage approach. Of the 65 patients included, 12 had been treated previously with resection or endovascular therapy. The mean AVM volume treated was about 15cm3 with a mean dose of 20 Gy with only one patient treated with <16Gy. The mean observation was 60 months with radiological imaging occurring every six months. 53 patients were followed for at least three years with 41 patients achieving obliteration by this time. The authors’ site rates of nidus obliteration after SRS of 44%, 76% and 81% at 3, 5 and 6 years respectively. Their annual hemorrhage rate was 1.94%.
Before recommending patients with large AVMs for SRS, one must consider that the total n for the study was small and the retrospective nature of the analysis also increases the chance for bias. In calculating the hemorrhage rate after SRS, patients who had bled after diagnosis but before SRS were excluded. Does this influence the natural history of hemorrhage after SRS? Of the 41 patients whose lesions were obliterated, only 18 patients maintained complete obliteration until 3 years after treatment. One of the recognized disadvantages of SRS is that it is usually inadequate by itself to permanently obliterate the AVM. Is this an acceptable risk in single SRS?
It has also been previously documented that smaller AVMs have a greater risk of hemorrhage than larger AVMs due to the suspicion that they are under greater pressure secondary to the smaller area. With this in mind, are larger doses of radiation used to treat larger lesions worth the benefit? If the answer is no, then the necessity of treatment comes into question. Just because a procedure can be performed, does it necessarily mean that it is warranted?
Large scale AVMs remain without one best treatment strategy. This study importantly opens the door to considering single SRS for therapy, but for now, the clinicians will need to continue to carefully weight risks and benefits while awaiting the availability of further research.