Thrombus formation can be caused by hypercoagulable states, systolic dysfunction with wall motion abnormalities, atrial fibrillation, valvular abnormalities, or artificial devices. Thrombi are the most common cause of an intracardiac mass. These are most common in LA and LV. They are at increased risk for systemic embolism.

It typically appears as a hypodense, low-attenuation filling defect in a contrast pool within a cardiac chamber and may be differentiated from primary and secondary tumors by knowledge of predisposing risk factors, attachment location, shape, and lack of mobility. But it is not without false positive and false negative diagnosis.

Chronic thrombi may develop spotty calcifications. Unfortunately, this feature has not been shown to significantly differentiate thrombus from atrial myxoma. The left atrial appendage (LAA) is the main location of thrombus formation, predominantly in patients with nonvalvular AF. Atrial thrombi, also commonly occur along the posterior wall of the LA. There are now cases of atrial thrombi arising from inter-atrial septum in the newly described left atrial septal pouch as another potential location of atrial thrombus.

Although useful imaging characteristics of myxomas and thrombi can be found on CT, potential overlap in the imaging findings may result in persisting uncertainty in the differentiation of the two disorders. Therefore, alternative imaging approaches such as MRI with superior tissue characterization with higher temporal resolution should also be considered.