AVM Surgery

Surgery has long been the gold standard for the treatment of intracranial AVMs. The most significant development to occur in this field has been the introduction and generalization of microsurgical techniques. In a series of more than 1200 patients treated over a 50-year period, a fivefold decrease in the mortality rate and a twofold decrease in the morbidity rate were documented for patients who underwent microsurgery as opposed to conventional surgery (16). Microsurgical resection of a small AVM located in the superficial or noneloquent brain achieves high-cure rates with low morbidity and remains the treatment of choice for such lesions (17). Besides microsurgery, such new technologies as functional MR imaging, intra operative electrophysiologic cortical mapping, and neurosurgical navigation systems have also helped to decrease surgical morbidity and mortality. Functional MR imaging is a sensitive planning tool when used to detect critical cortical areas in patients with AVMs located near the language centers (18). Intraoperative stimulation mapping and corticography play a similar role during resection of AVMs located within eloquent tissue. Stimulation mapping can be used to delineate motor, sensory, and language areas, thus decreasing the risk of neurologic deficits during excision of critically located AVMs (19). Intraoperative DSA also plays an important role in the efficacy and safety of AVM resection by allowing precise localization of the nidus and its different feeders as the resection progresses and confirming the completeness of the treatment before skull closure (14). The latter is particularly important, as subtotal resection of cerebral AVMs alone does not reduce the risk of bleeding from the lesion (20). Embolization of an AVM as a preparation to the surgical resection also helps to decrease the surgical risk and will be discussed later in this chapter.

The reported efficacy of surgery in obtaining an angiographic cure ranges between 94% and 100%. The likelihood of angiographic cure varies slightly with the AVM location: Complete obliteration has been reported in 100% of patients with AVMs located in the Sylvian fissure or in the lateral ventricles and in 89% of patients with brain stem lesion (11). The efficacy of surgery also varies with the Spetzler-Martin grade of AVM (21). Larger AVMs and those with deep-draining veins are understandably associated with an increased operative risk. In general, AVMs < 4 cm located in noneloquent cortex can be resected with a 5% risk of complication, whereas the surgical risk of larger AVMs located adjacent to or within functional areas can be 10% to 20% (9). The risk of permanent major neurologic morbidity has been reported to be 0% in patients with Spetzler-Martin grade I, II, and III AVMs, whereas patients with grade IV and V AVMs had permanent, major, neurologic deficit rates of 22% and 17%, respectively (22). A retrospective assessment of the determinants of neurologic outcome in 124 patients who underwent surgical resection of their AVMs, at a mean follow-up duration of 12 months, revealed that the rates of disabling and nondisabling neurologic deficits were 6% and 32%, respectively (11,23). The clinical presentation obviously influences the functional outcome. One series showed that patients who presented with ruptured AVM and underwent microsurgical resection tended to improve clinically after therapy, whereas patients treated for unruptured AVMs were more susceptible to worsening of their neurologic function. The mean change in Modified Rankin Scale was +0.89 for patients with a ruptured AVM and -0.38 for patients with unruptured AVM (24).

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