Free-floating thrombus in the carotid artery causing watershed cerebral infarction

A 39-year-old female with a history of hypertension presented at the emergency department with sudden onset right-sided weakness and speech disturbances lasting six hours. Neurological examination revealed right hemiparesis, dysarthria and mild cognitive impairment with intact cranial nerve functions. Vitals were: blood pressure 150/90 mmHg, pulse 78 bpm, regular.

MRI imaging weighted images—DWI (Figure 1a), ADC (Figure 1b), and FLAIR (Figure 1c)—demonstrated acute watershed infarct between the left anterior cerebral artery and middle cerebral artery territory. On Doppler ultrasonography, an echogenic intraluminal structure was identified in the left internal carotid artery, suggestive of a thrombus. CT angiography (CTA) confirmed a free-floating thrombus in the left internal carotid artery with no significant underlying atherosclerotic stenosis (Figures 2a, 2b and 2c).

Later laboratory tests showed elevated D-dimer (2.5 mg/L) and normal coagulation profile. The lipid profile showed elevated LDL cholesterol (140 mg/dL).

Background

A carotid free-floating thrombus (FFT) is defined as an elongated thrombus that is partially attached to the internal carotid artery wall, allowing blood to flow circumferentially around it [1]. It is often associated with hypercoagulable states, arterial injury, or cardioembolic phenomena [2]. It is especially significant due to the risk of embolic ischemia. Watershed infarcts, resulting from hypoperfusion or embolisation, typically involve junctional brain territories, where the perfusion pressure is lowest.

Clinical Perspective

Patients often exhibit acute neurological symptoms, such as transient ischemic attacks or strokes, accompanied by a significant risk of recurrence [3]. Imaging is essential for identifying the cause and guiding treatment. FFT poses a high risk for recurrent embolisation, requiring prompt detection and intervention. Physicians should be informed about the thrombus’ location, mobility, and embolic risk to optimise treatment planning.

Imaging Perspective

Key findings include a mobile intraluminal filling defect without significant arterial stenosis on Doppler and CTA. Non-invasive imaging, including Doppler ultrasound, is pivotal for screening, while CTA or magnetic resonance angiography (MRA) provides detailed visualisation of thrombus morphology and associated vascular abnormalities. Definitive diagnosis of FFT relies on dynamic imaging to confirm mobility, distinguishing it from stable plaque-associated thrombi.

Outcome

The management of FFT includes anticoagulation, endovascular thrombectomy, or carotid endarterectomy. In this case, anticoagulation with unfractionated heparin followed by endovascular thrombectomy resolved the thrombus and restored arterial patency. Prognosis is generally favourable with timely intervention, and imaging significantly impacts therapy planning by identifying patients requiring urgent surgical or endovascular treatment [4].

Take Home Message / Teaching Points

• Free-floating thrombus (FFT) in the internal carotid artery is a rare but critical condition requiring urgent diagnosis.
• Imaging plays a crucial role in identifying FFT and its complications.
• Early intervention prevents recurrent strokes and improves outcomes.

Written informed patient consent for publication has been obtained.