Imaging Studies
High-quality imaging studies are the key to diagnosis of arteriovenous malformations (AVMs).
CT scan
CT scanning easily identifies an intracerebral hemorrhage, raising suspicion of AVM in a younger person or a patient without clear risk factors for hemorrhage.
CT scan can identify only large AVMs.
MRI
MRI is essential for initial diagnosis of AVMs.
AVMs appear as irregular or globoid masses anywhere within the hemispheres or brain stem, as shown in the images below.
Axial T2 MRI showing an arteriovenous malformation with hemorrhage, in the territory of the left posterior cerebral artery.
T1 axial MRI showing a small subcortical arteriovenous malformation in the right frontal lobe.
T2 coronal MRI showing an arteriovenous malformation in the left medial temporal lobe.
AVMs may be cortical, subcortical, or in deep gray or white matter.
Small, round, low-signal spots within or around the mass on T1, T2, or fluid-attenuated inversion recovery (FLAIR) sequences are the "flow voids" of feeding arteries, intranidal aneurysms, or draining veins.
If hemorrhage has occurred, the mass of blood may obscure other diagnostic features, requiring angiogram or follow-up MRI.
Low signal of extracellular hemosiderin may be seen around or within the AVM mass, indicating prior symptomatic or asymptomatic hemorrhage.
Larger aneurysms within the AVM or on feeding arteries may be identified occasionally.
Magnetic resonance angiography (MRA) may identify AVMs greater than 1 cm in size, as in the image below, but is inadequate to delineate the morphology of feeding arteries and draining veins; small aneurysms can be missed easily.
Magnetic resonance angiography showing a left medial temporal arteriovenous malformation.
A retrospective analysis demonstrated that silent intralesional microhemorrhage on CT/MRI may be a risk factor for intracerbral hemorrhage from a brain AVM rupture. [2]
Cerebral angiography
Angiogram, shown below, is required for hemodynamic assessment, which is essential for planning treatment.
Angiogram (anteroposterior view) showing an arteriovenous malformation in the deep left middle cerebral artery territory measuring approximately 3 cm in diameter, with a deep draining vein (arrow).
The morphology of the AVM determines the treatment algorithm. Important features include feeding arteries, venous drainage pattern, and arterial and venous aneurysms.
Ten to fifty-eight percent of patients with AVM have aneurysms located in vessels remote from the AVM, in arteries feeding the AVM, or within the nidus of the AVM itself.
Intranidal aneurysms may have a higher risk of rupture than those outside the bounds of the AVM.
Other important angiographic features may include kinking or ectasia of draining veins, which can cause venous congestion, thrombosis, or rupture; and stenosis of feeding arteries due to angiopathy caused by high-velocity, turbulent flow into the fistula.
Special expertise is required to perform superselective catheterization into AVM feeding arteries, which allows both pressure measurements and superselective anesthetic injections to map neurological function in and around the AVM (see Superselective angiography in Procedures).
Other Tests
Based on flow-velocity and resistance pattern, transcranial Doppler (TCD) has been demonstrated to be a noninvasive and cost-effective means to detect and follow brain arteriovenous malformations (AVMs). Recently, TCD has been found to be a reliable, safe, and noninvasive method to monitor the outcome of gamma knife surgery for brain AVMs. [10]
Procedures
Superselective angiography
Superselective angiography is performed with standard cerebral angiography, with access via a femoral artery puncture.
A special, flexible, directable catheter is threaded up into one of the main cerebral arteries (carotid or vertebral), then into sequentially smaller branch arteries, until the catheter tip is near or within the AVM nidus.
Pressure measurements can be obtained via a coaxial catheter. Higher feeding pressures increase the risk of subsequent hemorrhage.
Sodium amytal, an anesthetic agent, can be injected to produce temporary anesthesia of the area perfused by the artery. In this so-called "superselective Wada testing," language, memory, visual-spatial, sensory, and motor function can be tested during 5 minutes of anesthetic effect to determine whether "eloquent" function originates in that region, which would therefore be at risk for neurological deficits should that brain area be injured during embolization or surgery. Arteries directly feeding the AVM or "en passage" vessels that feed the AVM but continue past the AVM to feed normal brain tissue can be studied.
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Axial T2 MRI showing an arteriovenous malformation with hemorrhage, in the territory of the left posterior cerebral artery.
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T1 axial MRI showing a small subcortical arteriovenous malformation in the right frontal lobe.
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T2 coronal MRI showing an arteriovenous malformation in the left medial temporal lobe.
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Magnetic resonance angiography showing a left medial temporal arteriovenous malformation.
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Angiogram (anteroposterior view) showing an arteriovenous malformation in the deep left middle cerebral artery territory measuring approximately 3 cm in diameter, with a deep draining vein (arrow).
