Size determination of supratentorial arteriovenous malformations by MR, CT and angio.

Twenty patients with high-flow supratentorial arteriovenous malformations (AVMs) were studied by magnetic resonance imaging (MR), computed tomography (CT), and selective cerebral angiography. The size of the malformation measured on MR was found, in general, to be smaller than the size determined from angiographic films. This discrepancy increased as the size of the AVM increased. AVM size on CT and angiography was found to be essentially equivalent. The reason for these differences between MR and CT or angiography was the ability to separate out the draining veins by MR, whereas this was difficult on projection films and contrast enhanced CT. Calcification was more easily detected by CT than by MR. MR better detected hemorrhage, which could be mistaken for old infarction on CT. Foci of cystic change within the nidus of the AVM were equally evident on MR and CT. Due to its sensitivity in discriminating between AVM nidus and adjacent draining veins and MR's ability to show the AVM in three planes, MR appeared to be more accurate in defining the AVM nidus than either CT or cerebral angiography. Such accurate delineation is crucial in patients prior to stereotactic radiosurgery.