Palliative treatment of inoperable arteriovenous malformations

Successful arteriovenous malformations (AVM) treatment is dependent upon achievement of the outcome of complete AVM nidus obliteration that leads to elimination of future hemorrhage risk. Eliminating this hemorrhage risk must be balanced with the risks and the morbidity and mortality associated with treating these lesions. Consequently, it is important to understand the natural history of these vascular malformations and be familiar with the risks and outcomes of each treatment modality: Microsurgery, endovascular embolization, and stereotactic radiosurgery. The widely used Spetzler–Martin grading system, which classifies AVMs based on their size, eloquence of adjacent brain, and patterns of venous drainage was specifically designed to estimate morbidity and mortality associated with AVM surgery [1]. Complete microsurgical excision of Spetzler–Martin grades I and II AVMs is associated with minimal morbidity and mortality rates. Indeed, most AVMs of grades I to III can be operated on with relative safety by experienced vascular neurosurgeons. However, the same cannot be said for grade IV and V AVMs. These large, critically located malformations require extensive dissection in close proximity to essential brain regions, and the resection could be complicated by difficulties with controlling fragile deep vessels. In addition, obliteration of a large AVM shunt exposes surrounding normal vessels to a sudden increase in perfusion, which may result in vasogenic edema or even hemorrhage (the phenomenon that has been termed as “normal perfusion pressure breakthrough”). Morbidity rates within the early postoperative period following complete surgical obliteration of grade IV and V AVMs, often using preoperative embolization, are 31% and 50%, respectively. Permanent major neurological morbidity rates of 21.9% and 16.7%, respectively, are noted on follow-up for these lesions [2]. With deep perforating arterial supply or deep meningeal recruitment, combined morbidity and mortality rates could be as high as 44% [3]. Given the unacceptably high rates of surgical morbidity and mortality, which exceed the risks determined by the natural history of AVM, it is a matter of debate whether these high-grade lesions should or should not be treated.