architectural features include exact anatomic relationships of the nidus, feeding arteries, and draining veins as well as topographic relationships between AVM and adjacent brain MRI is sensitive in revealing subacute hemorrhage The AVM appears as a sponge-like structure with patchy signal loss, or flow voids, associated with feeding arteries or draining veins on T1-weighted sequences ( Fig 122.3 ) MRI and MRA in combination provide complementary information that facilitates understanding the threedimensional structure of the nidus, feeding arteries, and draining veins MRA currently cannot replace conventional cerebral angiography In the case of acute hemorrhage, the hematoma obscures all details of the AVM making MRA virtually useless This calls for direct use of cerebral angiography if the characteristics of the hematoma strongly suggest AVM as an etiology FIGURE 122.2 Coronal CT of the brain demonstrates intraventricular hemorrhage with communicating hydrocephalus with minimal interval increase in the ventricular dilatation Diffuse cerebral edema with narrowing of the CSF space is suggestive of increased intracranial pressure FIGURE 122.3 T1-weighted sagittal MRI demonstrates an AVM in the right corpus callosum with intraventricular hemorrhage with main feeding vessel from right pericallosal artery and draining into the right internal cerebral vein Management The currently used treatments for AVMs include: (1) Microsurgical resection only, (2) preoperative endovascular embolization followed by microsurgical resection, (3) stereotactic radiosurgery only, (4) preprocedural endovascular embolization followed by radiosurgical treatment, (5) endovascular embolization only, and (6) observation only The ultimate goal for all of these modalities is cure for the patient; however, the only way to achieve cure is with complete obliteration of the AVM Microsurgery is the gold standard for resection of small superficial AVMs that other methods of treatment must be measured against There is 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