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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.