The Role of Cardiovascular Magnetic Resonance (CMR) in Unmasking Atrial Masses: A Case Series

Description of Clinical Presentation: Atrial masses represent a diagnostic challenge with differential diagnosis including thrombus, benign neoplasms such as myxoma, and malignant tumors. Echocardiogram and CT often identify the presence of a mass but may not reliability distinguish its etiology. CMR offers superior tissue characterization providing critical information for accurate diagnosis and management. We aim to evaluate CMR findings in atrial masses with various etiologies.



Patient Cases


Patient 1 is a 72-year-old female with atrial fibrillation status post left atrial appendage occlusion device, CKD post-renal transplant, and CAD without symptoms referred after CT finding of possible myxoma versus thrombus.


Patient 2 is a previously healthy 28-year-old female who presented with fever, systemic symptoms, and chest pain, in whom echocardiography revealed a left atrial mass (Figure 2, panel A).


Patient 3 is a 72-year-old female with chronic heart failure, atrial fibrillation, right atrial mass seen on echocardiogram during prior COVID-19 infection and Staphylococcal bacteremia on vancomycin. Recent CT showed mass with high HU of 130-150 and on TEE cystic appearance of the mass was described.

Diagnostic Techniques and Their Most Important Findings: All patients underwent CMR on a Siemens Aera 1.5T MRI scanner for further tissue characterization.


CMR for patient 1 showed a well-circumscribed mass seen on the left atrial septum. Imaging revealed isointense T1, hypointense T2, and no LGE (Figure 1, panel F), findings that favored thrombus. There was interval reduction in the size of the mass on anticoagulation compared to size on CT.


CMR for patient 2 demonstrated a 5.6 x 4.4 cm mass with a broad attachment near the roof of the left atrium, and mass extension into pulmonary vein, isointense on T1, hyperintense on T2, and heterogenous delayed enhancement, features concerning for malignant tumor (Figure 2, panels B through F). Surgical resection revealed a spindle cell neoplasm with fibroblastic features, consistent with low-grade sarcoma.


CMR for patient 3 revealed a 3.5 cm mobile, pedunculated right atrial mass adjacent to the SVC, isointense to myocardium on standard T1- and T2-weighted images. Quantitative mapping showed heterogenous appearance of the mass and elevated T1 ( >1200 ms) and T2 ( >60 ms) values (Figure 3, panels E through G), indicating active inflammation. The lesion showed no enhancement on perfusion or delayed imaging (Figure 3, panels H and I) and was dark on inversion recovery sequences, findings most consistent with infected thrombus related to recent bacteremia.

Learning Points from this Case: CMR holds value in differentiating atrial masses between benign or malignant tumor, and thrombus. This case series highlights the role of CMR in refining diagnoses and guiding decisions regarding anticoagulation, surgery, or antimicrobial therapy in cases of atrial mass.

Figure 1. Multimodality Imaging of Left Atrial Thrombus
Figure 2. Multimodality Imaging of Left Atrial Mass (Low-Grade Sarcoma)
Figure 3. Cardiac Magnetic Resonance Images of an Infected Thrombus