414 A Real-World Diagnostic Algorithm for Identifying Carotid Artery Stenosis

Abstract Aim Eighty-five percent of ischaemic strokes are caused by extracranial atheromatous lesions involving a narrowing of the Internal Carotid Artery so accurate and timely diagnosis is vital for management. The aim of this study was to correlate CT angiogram (CTA) and ultrasound doppler (US) derived measurements of carotid artery stenosis (CAS), with a view to identify those cases where second modality is required to reduce potential errors. Method All consecutive carotid US and CTA examinations performed in 2021 and 2022 were included for comparison in this retrospective cohort study. Collected data was then reviewed and evaluated by a multidisciplinary team. North American Symptomatic Carotid Endarterectomy Trial (NASCET) and St Mary’s criteria were used to narrow down the percentage stenosis. Results There were fifty-one patients (102 carotid arteries) over this period who had both studies performed. Twenty-nine males and twenty-three females with a median age of seventy-three. Initial data analysis showed no discrepancy in ninety-one (90%) carotid arteries between both modalities. After MDT review, there were eight (7.1%) false positive results and three (2.9%) true positive (2 symptomatic & 1 asymptomatic). In three (2.9%) cases quantification was significantly inaccurate in the initial imaging modality because of heavily calcified vessels. Conclusions This study supports the use of US or CTA as a single modality in grading CAS. Heavily calcified vessels on the first test should be a ‘red flag’ for triggering further alternative imaging to reduce the risk of error. Persistent discrepancies even after the second modality will require a further modality e.g., enhanced magnetic resonance angiography.