ABSTRACT
The decision to surgically treat an intracranial arteriovenous malformation (AVM) is arrived at after a careful evaluation of the patient’s clinical presentation, a comparison of the treatment risk against the natural history risk of an untreated AVM, and a consideration of the risks associated with alternative treatments, such as radiosurgery and embolization. Before a surgical course of treatment is initiated, the total risk of treatment should be assessed, not only from the surgical procedure itself but also from any adjuvant treatment such as staged embolization. When an intracranial AVM is evaluated with the goal of complete surgical resection, there are a number of clinical, anatomic, and radiographic factors that can add risk and influence surgical difficulty. Size of nidus, close relationship to physiologically eloquent areas, and deep venous drainage have been correlated with surgical outcome (1). Heros et al., in a report of their series of surgically excised AVMs, found a good correlation between the Spetzler-Martin grade of the AVM and early outcomes (2). However, there are a number of additional factors that can directly influence surgical difficulty and thus potentially the outcome. Clinically, the presence of a previous hemorrhage cavity can facilitate the dissection of a difficult AVM as it provides a direct pathway from the cortical surface to the AVM nidus. Tew et al. noted that the presence of previous hemorrhage helped to define the surgical planes for resection of deep-seated caudothalamic AVMs (3). By contrast, the presence of previous hemorrhage can make the removal of an AVM technically more difficult as the nidus can become fragmented, thus increasing the chance of leaving a small residual piece not visualized during removal of the larger portion of the nidus. Anatomically, a number of factors can contribute to the difficulty of surgical resection, including a compact or diffuse nidus (angiomatous change), the presence of lenticulostriate or deep posterior cerebral artery (PCA) feeders, the presence of en passage vessels (Fig. 1), and nidal juxtaposition with eloquent cortex and vital white matter tracts. The presence of deep versus cortical venous drainage has not, in the authors’ experience, made the resection of an AVM more difficult as it is encountered late in dissection and is easier to work around. In fact, superficial drainage can complicate resection as it narrows surgical corridors and when retracted can increase AVM turgor. Complex AVMs, which have multiple arterial feeding pedicles with significant arterial supply from the contralateral hemisphere, recruitment of perforators, a paucity of filling of normal cortical branches (steal), and external carotid supply, are associated with an increased chance of the development of a hyperemic state during and after resection; this problem can lead to intraoperative edema and postoperative bleeding (4). A careful consideration of each of these factors before surgery can lead to a more accurate assessment of risk, a strategically designed treatment plan, a better prepared surgeon, and, it is hoped, a more successful outcome for the patient.
