Abstract 2636: Magnetic Resonance Angiography Measurement of Carotid Stenosis Underestimates Plaque Burden Identified by Magnetic Resonance Imaging
Measurement of carotid stenosis using NASCET criteria, where the minimum lumen diameter is compared to the normal distal artery, is often used as an indicator of atherosclerotic disease. However, stenosis measurement may fail to indicate plaque burden due to the geometry of the carotid bulb and because of expansive, compensatory remodeling. This study assessed the prevalence and characteristics of atheroma amongst subjects with zero percent stenosis by magnetic resonance angiography (MRA). Sixty-six mainland Chinese subjects with >50% carotid stenosis in at least one carotid artery underwent bilateral carotid artery MRA at 3.0T (GE Signa Excite) to determine the degree of stenosis. Multi-contrast weighted magnetic resonance imaging (MRI) scans were then performed to identify plaque features. Luminal stenosis was quantified in both carotid arteries using NASCET criteria. Using previously validated MRI criteria, the subset of carotid arteries with zero percent stenosis by MRA were assessed for vessel wall thickness and presence of a lipid-rich necrotic core (LRNC). Fibrous cap status was determined amongst arteries with a LRNC. Seven arteries were excluded from analysis because of poor image quality. Of the remaining 125 arteries, 41 (32.8%) displayed no stenosis by MRA. Thirty-five of the 41 non-stenotic arteries (85.4%) demonstrated eccentric lesions on cross-sectional MRI. Arteries with plaque present compared to those without had a significantly larger maximum wall thickness (1.96±0.57 vs. 1.16±0.11 mm ; p<0.001). Amongst the 41 non-stenotic arteries, 70.7% (29/41) had a LRNC, 44.8% (13/29) had an intact thick fibrous cap, 41.4% (12/29) had an intact thin fibrous cap; and 13.8% (4/29) had fibrous cap disruption. Amongst mainland Chinese with a >50% unilateral carotid stenosis, non-stenotic contra-lateral carotid atherosclerosis was frequently observed. Moreover, complex features such as LRNC and thin or disrupted fibrous caps were common in this subgroup. These findings indicate that measurement of stenosis using NASCET criteria underestimates the presence of carotid atheroma, and demonstrates the need for improved methods for identifying high-risk carotid plaque.