Ultrasonographic Morphology Assessment of Low-grade Carotid Stenosis

Overview

Internal carotid artery (ICA) is intended to supply blood to brain. The carotid bulb located upstream of ICA origin is prone to atherosclerosis. This is an accumulation of fat and calcium in the wall forming a plaque that gradually thickens and leads to carotid stenosis (CS), which causes a decrease in blood flow. The risk of CS is stroke caused either by carotid artery thrombosis (occlusion) or by atherosclerotic plaque fragmentation, some components of which may leak into the brain (embolism). When diagnosing CS, an Echo-Doppler is performed to determine bulb and ICA origin obstruction rates. The reference method of quantifying CS is based on hemodynamic criteria that only allow the diagnosis of high grade stenosis thresholds (50%-70%). Below 50%, low-grade stenosis, patient follow-up is limited and could be based on morphological criteria; ultrasound imaging being a reference technique for human body structures morphological assessment, especially vessels. Two methods of CS morphological quantification with Doppler ultrasound currently exist. Calibre reduction at the maximum of stenosis can be measured by relating the smallest luminal diameter to the vessel diameter at stenosis site (ECST method) or to the downstream ICA diameter (NASCET method). As bulb diameter measures ≈1.8 times that of ICA, ECST appears to be more suitable for CS quantification. For high-grade stenosis, morphological quantification performance is impaired due to extensive calcification of large atheromatous plaques. However, it is possible that less calcified nature of low-grade stenosis and the use of a rigorous methodology will allow reproducible assessment in routine practice. This technique has not yet been evaluated, although it is a frequent situation in patient follow-up.

Internal carotid artery is intended to supply blood to brain. The carotid bulb located upstream of internal carotid artery origin is prone to atherosclerosis. This is an accumulation of fat and calcium in the wall, forming a plaque which gradually thickens and leads to carotid stenosis, causing a reduction in blood flow. The risk of carotid stenosis is stroke caused either by carotid artery thrombosis (occlusion) or by atherosclerotic plaque fragmentation, some components of which may leak into the brain (embolism). When carotid stenosis is diagnosed, an Echo-Doppler is performed to determine the bulb and internal carotid artery origin obstruction rates. The reference method for quantifying carotid stenosis is based on hemodynamic criteria that only allow the diagnosis of high grade stenosis thresholds (50%-70%). Below 50%, low-grade stenosis, patient follow-up is limited and could be based on morphological criteria; ultrasound imaging being a reference technique for human body structures morphological assessment, especially vessels. Two methods of carotid stenosis morphological quantification with Doppler ultrasound currently exist. Calibre reduction at the maximum of stenosis can be measured by relating the smallest luminal diameter to the vessel diameter at stenosis site ("European Carotid Surgical Trial" (ECST), European method) or to the downstream internal carotid artery diameter ("North American Symptomatic Carotid Endarterectomy Trial" (NASCET), North American method). As bulb diameter measures ≈1.8 times that of the internal carotid artery, the NASCET appears to be more suitable for carotid stenosis quantification. For high-grade stenosis, morphological quantification performance is impaired due to extensive calcification of large atheromatous plaques. However, it is possible that less calcified nature of low-grade stenosis and the use of a rigorous methodology will allow reproducible assessment in routine practice. This technique has not yet been evaluated although it is a frequent situation in patient follow-up. This study therefore suggests to evaluate the inter-observer reproducibility of morphological quantification of these stenosis by the ECST method with a precise methodology.