Free-Floating Thrombus in Carotid Artery: Atherosclerosis and 'Donut Sign' on CTA

Revised: Atherosclerosis is the most common cause of free-floating thrombus in the carotid artery, with fibrous cap rupture being the primary culprit in approximately 90% of stroke-related thrombosis cases. When a plaque ruptures, the lipid's necrotic core is exposed to circulation, promoting thrombosis and leading to stroke events. Free-floating thrombus is characterized by a cylindrical thrombus attached to the arterial wall, surrounded by blood flow at the distal end, and exhibiting periodic movements related to the cardiac cycle. On CTA, it appears as a filling defect in the carotid artery lumen on at least two contiguous axial source images, surrounded by contrast agent, and extending to some extent in the direction of the head, described as the 'donut sign'. The ultrasonography features of this case align with the above imaging findings.