Definition of Carotid Artery Free Floating Thrombus: A Systematic Review and Call for Standardisation of Imaging and Nomenclature.

Objective: Free floating thrombus in the carotid artery (cFFT) is a rare and poorly understood condition with an unclear definition and diagnostic criteria. This systematic review aimed to propose a reporting standard to ensure diagnostic consistency and a universal definition of cFFT. Methods: PubMed and EMBASE were systematically searched from inception until 01 May 2025, using terms including "free floating thrombus" and "carotid", along with imaging modalities. Eligibility criteria included studies on patients with cFFT, diagnosed through well defined imaging criteria. Two authors independently screened eligible literature and extracted data. Study quality was assessed with the Methodological Index for Non-Randomized Studies (MINORS) score. The composite endpoint was the radiological description of cFFT per imaging modality. Results: A systematic search identified 611 publications, from which 20 were included. These studies were predominantly of low quality, with a mean MINORS score of 9 for non-comparative and 16 for comparative studies. These 20 studies identified 17 distinct imaging based descriptions of cFFT. The descriptions were derived from five different imaging modalities, encompassing both static and dynamic imaging. Computed tomography angiography (CTA) was the most reported modality, followed by duplex ultrasound (DUS). On CTA, cFFT is diagnosed as a thrombus with circumferential flow, proximal attachment to the vessel wall, and extending distally in the lumen. On DUS, cFFT is diagnosed by circumferential flow, attachment to the arterial wall, and synchronous movement with the cardiac cycle. Conclusion: The published literature lacks high quality studies. It is suggested that the diagnosis of cFFT requires static imaging, preferably with CTA. If static imaging is inconclusive, a dedicated dynamic assessment by DUS, performed by an experienced sonographer, is suggested. The proposed definition aims to standardise the diagnostic workflow for cFFT, thereby ensuring consistent interpretation and unified terminology across research and clinical practice, which should also enhance individual patient data meta-analyses on cFFT in the future.