Studying plaque characteristics in extracranial carotid artery disease using CT angiography - Risk predictors beyond luminal stenosis.

OBJECTIVES: Carotid atherosclerosis accounts for around 20 % of ischemic strokes. Literature on CT angiography [CTA] to study plaque morphology is limited. We studied plaque characteristics of extracranial carotid arteries using CTA to ascertain the high risk features beyond luminal stenosis. MATERIALS AND METHODS: Retrospective study design, where patients with carotid territory ischemia who underwent CTA from January 2011 till December 2015 were recruited from medical records. CT images were reviewed for plaque characteristics like attenuation, ulceration, plaque thickness and presence of intraluminal thrombus [ILT] along with percentage stenosis. RESULTS: 114 patients with 201 carotids [102 symptomatic and 99 asymptomatic] were reviewed. Mixed density plaques [p = 0.05], ulceration [p = 0.001], ILT [p = 0.004] and higher soft plaque thickness [p < 0.001] were significantly associated with symptomatic carotids whereas calcified plaques were seen in asymptomatic carotids [p = 0.005]. Plaque characteristics were comparable in symptomatic patients with moderate[50-69 %] and severe[70-99 %] stenosis. Multivariate analysis showed that increased soft plaque thickness remained significantly associated with symptomatic carotid. A cut-off value for soft plaque thickness of 2.75 mm could predict symptomatic carotid disease with a sensitivity of 85.2 % and specificity of 68.0 % [Youden's index]. An increase in soft plaque thickness of 4.0 mm significantly predicts change from asymptomatic to symptomatic carotid [p < 0.05]. CONCLUSIONS: Of the studied CTA plaque characteristics, soft plaque thickness is an independent predictor of symptomatic disease irrespective of the percentage stenosis. Soft plaque thickness over 2.75 mm and smallest detectable change[4 mm] are new measures to help ascertain the risk of ischemic events in carotid atherosclerotic disease.