Intracranial Vessel Wall MRI: Principles and Expert Consensus Recommendations of the American Society of Neuroradiology

Abstract

Intracranial vessel wall MR imaging is an adjunct to conventional angiographic imaging with CTA, MRA, or DSA. The technique has multiple potential uses in the context of ischemic stroke and intracranial hemorrhage. There remain gaps in our understanding of intracranial vessel wall MR imaging findings and research is ongoing, but the technique is already used on a clinical basis at many centers. This article, on behalf of the Vessel Wall Imaging Study Group of the American Society of Neuroradiology, provides expert consensus recommendations for current clinical practice.

Fig 1.

Technical implementation of VW-MR imaging. Comparison of a coronal 2D T1-weighted FLAIR VW-MR imaging sequence (A) and a 3D proton-density–weighted variable flip angle refocusing pulse, fast spin-echo VW-MR imaging sequence (B) in a healthy subject. Insets show magnified images of the carotid terminations with arrows pointing to the arterial wall. Comparison of a standard contrast-enhanced T1-weighted spin-echo sequence (C) and an optimized contrast-enhanced T1-weighted VW-MR imaging sequence (D) shows how blood suppression is needed to reveal an enhancing atherosclerotic plaque (arrow) in the left MCA M1 segment.

Fig 2.

VW-MR imaging to differentiate among causes of intracranial arterial stenosis when angiography findings are inconclusive. This patient had multiple recent infarcts in the pons. MR angiogram (A) demonstrates short segments of mild narrowing of the distal basilar artery (arrowheads) and left superior cerebellar and posterior cerebral arteries (arrows). Axial T1-weighted VW-MR imaging before (B) and after (C) intravenous contrast injection shows smooth concentric enhancement of the basilar artery wall (arrow). VW-MR imaging before (D) and after (E) contrast injection shows similar enhancement of the left posterior cerebral artery wall (arrow). The vessel wall appearance is consistent with the final diagnosis, which was primary CNS vasculitis. For comparison, coronal contrast-enhanced T1-weighted VW-MR imaging (F) in a different patient shows characteristic features of an atherosclerotic plaque: eccentric arterial wall thickening with a contrast-enhancing fibrous cap (long white arrow) and peripheral nonenhancing plaque (black arrow). A short white arrow points to the arterial lumen.

Fig 3.

VW-MR imaging to identify symptomatic, nonstenotic intracranial atherosclerotic plaque. A 52-year-old man with a previous transient ischemic attack attributable to the right middle cerebral artery territory presented with an acute infarct (A) in the same vascular territory. Cardiac work-up, CT angiography of the head and neck and DSA (B and C) and cervical carotid VW-MR imaging failed to identify a cause of the stroke. Sagittal-oblique contrast-enhanced T1-weighted VW-MR imaging of the supraclinoid segment of the right ICA (D) shows eccentric arterial wall thickening (arrows) with enhancement (dotted arrow) in the more luminal aspect of the thickening, consistent with the fibrous cap of a recently symptomatic plaque. Sagittal-oblique T2-weighted VW-MR imaging (E) shows T2 prolongation (arrow) in the more luminal aspect of the thickening and T2 shortening peripherally, consistent with the fibrous cap and lipid core of atherosclerotic plaque, respectively. The arterial wall thickening without luminal narrowing is so-called positive remodeling of the vessel wall.

Fig 4.

VW-MR imaging to diagnose intracranial arterial dissection with minimal luminal narrowing. A 57-year-old man presented to the emergency department with severe headache and neck pain for 1 week. 3D rendering of a CTA shows smooth narrowing of the intradural segment of the right vertebral artery (A, arrows). This angiographic appearance was considered most likely within the range of normal because the vertebral artery is commonly narrower beyond the posterior inferior cerebellar artery origin, but a bit equivocal. Coronal (B) and axial (C) nonenhanced T1-weighted VW-MR imaging shows eccentric intense hyperintensity (B and C, arrows) in the wall of the right vertebral artery, consistent with recent arterial dissection.

Fig 5.

VW-MR imaging to evaluate vascular disease activity. MR angiogram demonstrates a saccular aneurysm at the tip of the basilar artery (A) and a saccular aneurysm at the right posterior communicating artery origin (C). Coronal contrast-enhanced T1-weighted VW-MR imaging shows no enhancement of the basilar artery aneurysm wall (B, arrow) but intense enhancement of the posterior communicating artery aneurysm wall (D, arrow). Axial T2-weighted FLAIR image (E, arrow) demonstrates a hematoma centered around the enhancing aneurysm, consistent with the preliminary research studies, suggesting that symptomatic and ruptured aneurysms have wall enhancement much more commonly than asymptomatic saccular aneurysms.

Fig 6.

Common VW-MR imaging pitfalls. Case 1 (A and B) shows how slow flow can mimic arterial wall disease. Axial nonenhanced T1-weighted VW-MR imaging (A) demonstrates a crescent (arrow) of intermediate-to-hyperintense signal at the periphery of the basilar artery, suggestive of arterial wall thickening from dissection or atherosclerotic plaque. A corresponding image from a gadolinium-enhanced MRA (B) shows that the crescent of apparent arterial wall thickening fills with contrast and therefore represents a dilated basilar artery lumen rather than the arterial wall. Case 2 (C) shows how vasa vasorum can mimic vasculitis. Coronal contrast-enhanced T1-weighted VW-MR imaging shows a focal atherosclerotic plaque (white arrow) of the basilar artery, but also more diffuse smooth concentric enhancement of the vertebral (black arrows) and basilar artery walls, which has an appearance similar to that of vasculitis. The diffuse enhancement is consistent with increased intracranial vasa vasorum in this patient who has strong atherosclerotic risk factors. Case 3 (D) shows how a normal vein residing close to an artery can mimic arterial wall disease, such as enhancing atherosclerotic plaque. Axial contrast-enhanced T1-weighted VW-MR imaging shows a vein (arrow) adjacent to the left middle cerebral artery.