Abstract 167: High Resolution MR Imaging Of Intracranial Arterial Vessel Walls In Moyamoya Disease

Abstract

Background: The pathogenesis of the primary occlusive vasculopathy or vasculopathies involving the basal arteries in patients with moyamoya phenomenon is unknown. Newer Magnetic Resonance (MR) techniques have been developed to characterize atheroma in the arterial wall. This is a pilot study of vessel wall imaging using high field-strength, high-spatial resolution MR techniques in patients with moyamoya. Method: Twenty patients with idiopathic moyamoya were recruited. MR imaging was performed on a 3T head MR system. Imaging included a time-of-flight (TOF) magnetic resonance angiography (MRA) and high-resolution T2-weighted sequences through the circle of Willis. Images were inspected for evidence of an intramural occlusive lesion or atheroma. Vessel wall thickness of the internal carotid artery (ICA) at the points of maximal narrowing as determined by catheter angiography was compared to the wall thickness of the distal basilar artery in each patient. Vessel wall thickness was calculated as the difference between the intraluminal diameter measured on MRA and the extraluminal diameter measured on the T2 image, divided by 2. Results: All patients demonstrated diminished arterial diameters on T2 imaging corresponding to sites of luminal stenosis on catheter angiography and time-of-flight MRA sequences. No focal or diffuse intramural thickening was subjectively observed at the sites of stenosis. Objective measures of vessel wall thickness found no difference between the sites of maximal stenosis of involvded vessels and univolved vessels of similar diameter. The mean thickness of the basilar artery was 0.66 mm (standard deviation 0.14). The mean thickness of the diseased ICA was 0.61 mm (s.d. 0.22) in patients with bilateral disease. The mean thickness of the uninvolved ICA in patients with unilateral disease was 0.69 mm (s.d. 0.07). The figure includes sequential high resolution T2 images of a patients with unilateral right sided moyamoya phenomenon (a,b) demonstrating a small right ICA (arrow) compared to the unaffected contralateral ICA. TOF MRA (c,d) illustrate luminal stenosis without evidence of intramural thickening. Multiple moyamoya collateral vessels are also evident (c). Conclusion: These data suggest that the pathological process underlying vessel narrowing and occlusion is not a static structural lesion in the vessel wall leading to luminal compromise. In addition, these imaging techniques may be useful in distinguishing idiopathic basal occlusive disease from other processes such as atherosclosis.