When an AVM is suspected, a CT scan (computerized tomography) is likely to be the first test performed because it is quick, easy and widely available in most hospitals. CTs are painless and non-invasive.
If an AVM has bled, the CT scan will typically show the blood and may suggest the presence of the AVM itself. When no bleed has occurred, the CT scan may show that an AVM is present in the brain or may show an area of abnormality. In these cases, the next step will be an MRI (magnetic resonance imaging) for a more definitive diagnosis. When an AVM is known to be present and a bleed is suspected, a CT scan is preferred over MRI as the best radiology test in showing blood that has escaped from an AVM.
MRI is a sophisticated test that takes longer than a CT scan (up to an hour) and gives a more detailed picture of the brain. An MRI typically does an excellent job of showing the tangled and abnormally enlarged blood vessels of a brain AVM.
Arteriograms & angiograms
Another test to show the details of an AVM is a cerebral arteriogram or angiogram. The doctor first passes a catheter up from an artery in the groin to the arteries in the neck, and then injects dye into the carotid and vertebral arteries while multiple x-rays are taken of the arteries in the brain. This provides a detailed view of the AVM that helps in planning treatment.