A simple semi-quantitative score based on FDG-PET and CT angiography can help for the evaluation of stenotic carotid atherosclerotic plaques in symptomatic and asymptomatic patients.

Objectives In this study, we developed a simple semi-quantitative score for the classification of carotid plaques in patients with symptomatic carotid plaque, based on morphological and functional imaging criteria extracted from FDG-PET and CT angiography, respectively. We then tested the prognostic value of this score in a cohort of asymptomatic patients with carotid stenosis.

Methods A total of 54 patients with carotid plaques were imaged with PET 2 hours after injection of 4 MBq/ kg of FDG followed by CTA of the supra-aortic trunks. Morphological aspects of plaques identified with CTA and metabolic activity quantified with FDG-PET (Tissue to Background ratio, TBR) were measured in the region of the operated carotid artery with the highest degree of luminal stenosis and graded using semi-quantitative CT based on plaque morphology (maximal score = 6) and PET scores based on the intensity of FDG uptake in the carotid plaque (maximal score = 4). A combined score was calculated for each carotid artery by summing the CT and PET scores (maximal score = 10). The combined score was first tested in 23 patients undergoing carotid endarterectomy. Plaque obtained after carotid endarterectomy was classified as complicated (thrombus, plaque rupture or intra-plaque haemorrhage) or non-complicated. The combined score was then evaluated in a cohort of asymptomatic patients with carotid stenosis > 50 %. Patients were followed for the occurrence of clinical cerebral ischemic events or carotid endarterectomy showing the presence of complicated plaques.

Results A total of 54 patients with carotid stenosis > 50 % (31 symptomatic; 23 asymptomatic) were imaged in this study. Among the 29 atherosclerotic plaques obtained from carotid endarterectomy, 23 plaques were classified macroscopically as complicated. The combined score measured in complicated vs. non-complicated plaques was 6.1 ± 1.9 vs. 3.7 ± 2.0 (p < 0,05). A combined score 蠅 4 identified complicated plaques with a sensitivity of 90 % and a specificity of 67 % (accuracy 83%). We then tested this threshold value of combined score in the cohort of patients with carotid stenosis > 50 % but not scheduled for carotid endarterectomy (n = 16). During a mean follow-up of 13 ± 9 months, 5 patients (1 acute ischemic cerebral event, 4 carotid endartectomy with complicated plaques) met the primary endpoint: 4 patients in the group with combined score 蠅 4 and 1 in the group of a combined score < 4 (odds ratio = 3,9 for a combined score 蠅 4).

Conclusions A simple semi-quantitative score based on combined FDG-PET-CTA imaging can help for the identification of complicated carotid plaques in symptomatic patients. In a small cohort of asymptomatic patients with carotid stenosis > 50 %, we found that a score >= 4 was associated with an increased risk of acute cerebral ischemic events or carotid endarterectomy showing complicated plaques. The value of this score for risk stratification of asymptomatic patients with carotid stenosis will need to be confirmed in a larger group of patients.