ABSTRACT NUMBER: ESOC2026A504 LIMITATIONS OF NASCET CRITERIA IN MEASURING CAROTID BULB STENOSIS: IS IT TIME TO CONSIDER ALTERNATIVE MEASUREMENT APPROACHES?

Abstract Background and aims The North American Symptomatic Carotid Endarterectomy Trial (NASCET) method is the guideline-endorsed standard for quantifying internal carotid artery (ICA) stenosis. However, the method uses the distal ICA as a reference diameter, which is inherently smaller than the carotid bulb where atherosclerotic disease most commonly occurs. The purpose of this review is to explore the geometric limitation of NASCET measurement in carotid bulb stenosis, evaluate whether adjustment is possible, and compare alternative stenosis measurement methodologies. Methods Conceptual and geometric analysis of NASCET, European Carotid Surgery Trial (ECST), common carotid artery (CCA) based , and area-based stenosis measurement methods was performed, supported by diagrammatic comparisons and literature review. Results NASCET systematically underestimates stenosis severity for bulb-based lesions due to mismatch between reference and native vessel diameter. This is more pronounced in case of "Giant bulb" where the bulb diameter is greater than 10 mm. No validated adjustment factor exists within the NASCET framework. Alternative methods such as ECST and area stenosis account for bulb anatomy but are not interchangeable with NASCET and lack guideline equivalence. Conclusions Despite its geometric limitations, NASCET remains the clinical standard. When stenosis is located in the carotid bulb, radiologists should acknowledge potential underestimation and may provide supplementary anatomic context without altering NASCET values. Further research is required in this area and identification of high risk markers on other imaging modalities like dedicated vessel wall imaging and Doppler ultrasound characteristics of the atherosclerotic plaque should be considered in clinical practice. Conflict of interest Saeedur Rahman: Nothing to disclose