A Pseudo-Right Atrial Mass in Massive Pulmonary Embolism: A Case Report Highlighting Multimodality Imaging and Multidisciplinary Team Review

Transthoracic echocardiography (TTE) is often the first-line imaging modality in cardiac assessment due to its accessibility and rapid acquisition. However, compared with cardiac magnetic resonance (CMR), it offers limited tissue characterisation and may misinterpret anatomical variants as pathology. Consequently, multimodality imaging and multidisciplinary team (MDT) review are frequently required for accurate diagnosis. A 44-year-old man presented with acute dyspnoea following long-haul travel. Computerised tomography pulmonary angiography revealed massive bilateral pulmonary emboli without right ventricular strain, and he was treated with rivaroxaban 20 mg once a day. Three months later, follow-up TTE demonstrated a right atrial mass, reported as a possible thrombus, prompting anticoagulation change to warfarin. At six months, CMR showed no intracardiac mass. However, repeat TTE at one year again suggested a right atrial mass. A review during the cardiac imaging MDT concluded that the apparent "mass" represented epicardial fat entering the imaging plane. Rivaroxaban 20 mg once a day was reinstated for indefinite anticoagulation. This diagnostic pitfall led to an unnecessary switch to warfarin, highlighting how misinterpretation of anatomical variants can significantly alter clinical management. This case underscores the critical role of multimodality imaging and MDT review in the evaluation of intracardiac masses to prevent misdiagnosis and unnecessary treatment.