Objective: To validate a previously proposed filling defect length threshold of >3.8 mm on CT-angiography (CTA) to discriminate between free-floating thrombus (FFT) and plaque of atheroma.

Materials and Methods: Prospective multicenter observational study of 100 participants presenting with TIA/stroke symptoms and a carotid intraluminal filling defect on initial CTA.  Follow-up CTA was obtained within one week, and at weeks 2 and 4 if the intraluminal filling defect was unchanged in length.  Resolution or decreased length was diagnostic of FFT, whereas its static appearance after 4 weeks was indicative of plaque. Diagnostic accuracy of FFT length was assessed by receiver operating characteristic analysis.

Results: Ninety-five participants (mean age [standard deviation], 68 [13] years; 61 men; 83 participants with FFT; 12 participants with a plaque) were evaluated. The >3.8 mm threshold had a sensitivity of 88% (73/83) (95% confidence interval {CI}: 78%, 94%) and specificity of 83% (10/12) (95% CI, 51%, 97%) (area under the curve [AUC], 0.91, p<.001) for the diagnosis of FFT. The optimal length threshold was >3.64 mm with a sensitivity of 89%( 74/83) (95% CI, 80%, 95%) and specificity of 83% (10/12) (95% CI, 51%, 97%). Adjusted logistic regression showed that every 1 mm increase in intraluminal filling defect length is associated with an increase in odds of FFT of 4.6 ([95% CI] 1.9-11.1; p=.01).

Conclusion: CTA enables accurate differentiation of FFT versus plaque using craniocaudal length thresholds.

Clinical Trial Identifier: www.clinicaltrials.gov NCT02405845.

Classification of Evidence: This study provides Class I evidence that in patients with TIA/stroke symptoms, the presence of a carotid intraluminal filling defect with length > 3.8 mm on CTA accurately discriminates free-floating thrombus from atheromatous plaque.

Standard Protocol Approvals, Registration, and Participant Consents: this prospective multicenter observational study was approved by the institutional ethics boards (REB: 20150092-01H; REB:16-391; REB: 15-2456; clinical trial identifier: www.clinicaltrials.gov (NCT02405845). Informed consent was obtained from participants. This study was reported following the guidelines of the Standards for Reporting of Diagnostic Accuracy Studies (STARD).¹⁷

Primary Research Question and Classification of Evidence

Primary research question: Can CTA discriminate between free-floating thrombus (FFT) and plaque in patients with stroke/TIA?

This study provides Class I evidence that in patients with TIA/stroke symptoms, the presence of a carotid intraluminal filling defect with length > 3.8 mm on CTA accurately discriminates free-floating thrombus from atheromatous plaque.