certainly a well-established role for adjunctive endovascular embolization of some AVMs Clearly, there are specific situations, such as small deep AVMs in eloquent brain structures, where microsurgery should not be used as the primary treatment modality; stereotactic radiosurgery and occasionally embolization (when there is reasonable expectation of complete obliteration by embolization) are the preferred treatment options in these cases We also make a case for observation in patients with large AVMs in or near critical areas of the brain that are not ideal for surgical resection or radiosurgery Here, the pursuit of treatment may actually be more harmful to the patient than the natural history of the AVM Indications for Surgical Resection There are several clear indications for microsurgical resection of AVMs AVMs with Spetzler–Martin grades I to III on the convexity should generally be resected The Spetzler–Martin grading system takes into account three factors that greatly affect the surgical resectability of the AVM: size (6 cm, points), location (noneloquent cortex, points; eloquent cortex, point), and venous drainage (superficial only, points; deep, point) Patients with AVMs that present with major hemorrhage, progressive neurologic deterioration, inadequately controlled seizures, intractable headache, or venous restrictive disease should be strongly considered for surgical intervention, including resection, hematoma evacuation, or acute spinal fluid diversion Cerebellar and pial brainstem AVMs should also be given strong consideration for surgical resection to prevent the higher risk of bleeding as compared to supratentorial AVMs Some basal ganglia and thalamic AVMs should be surgically resected, as they carry a considerably higher annual bleed rate of 11.4%; in addition, morbidity and mortality with each bleed in these locations reach 7.1% and 42.9%, respectively (again, in contrast to the overall mortality rate of AVM hemorrhage of 10%) Hence, one may justify a more aggressive approach for surgical treatment in younger patients as their cumulative risk of hemorrhage is so high In addition, neurologic deficit caused at a young age is generally better tolerated and has a greater chance of recovery ACUTE HYDROCEPHALUS