Maximum stenosis of extracranial internal carotid artery: Effect of luminal morphology on stenosis measurement by using CT angiography and conventional DSA

PURPOSE: To assess the luminal morphology of the extracranial internal carotid artery at three-dimensional (3D) computed tomographic (CT) angiography and how this factor affects measurement of maximum carotid arterial stenoses at conventional intraarterial digital subtraction angiography (DSA). MATERIALS AND METHODS: Prospectively, conventional intraarterial DSA and 3D CT angiography were performed in 42 carotid arteries in 21 patients with suspected carotid artery disease. The longest axis length-perpendicular axis length (L/P) ratios of the arterial lumen on the cross-sectional images at the most stenotic area and distal nonstenotic area were analyzed by acquiring multiplanar reconstruction (MPR) images at 3D CT angiography. The maximum stenosis was measured at each modality with North American Symptomatic Carotid Endarterectomy Trial criteria. RESULTS: The L/P ratios in the most stenotic areas ranged from 1.0 to 3.2 (mean, 1.5 +/- 0.5 [SD]). The mean difference in maximum percentage of stenosis between the two modalities for L/P ratios of 2.0 or greater was significantly greater than that 70%-99% stenosis, with grades determined only with 3D CT angiography, had L/P ratios of 2.0 or greater. CONCLUSION: On MPR images at 3D CT angiography, the lumen of extracranial internal carotid artery stenosis showed a wide range of shapes. When a carotid artery has a high L/P ratio, the luminal morphology of the carotid artery stenosis may affect the assessment of maximum stenosis of the internal carotid artery at conventional DSA.