Diffuse Large B-cell Lymphoma Presenting as a Cardiac Mass

Cardiac involvement as the initial presentation of lymphoma is a rare occurrence. The most common type of cardiac lymphoma is diffuse large B-cell lymphoma (DLBCL), which often affects the right atrium. Cardiac lymphoma can either be mediastinal DLBCL invading the heart or primary cardiac lymphoma. We describe the case of an 84-year-old female who presented with an eight-week history of dyspnea. Computed tomography angiography (CTA) of the chest showed a right-sided pleural effusion with collapse of the right middle and lower lobes as well as a large mass-like density within the anterior pericardium, compressing the right atrium and right ventricle and encasing the right coronary artery. A transthoracic echocardiogram (TTE) showed a multilocular hypoechoic mass in the right atrium with invasion into the wall of the right atrium. The patient underwent diagnostic and therapeutic thoracentesis. Pleural fluid cytology revealed diffuse large B-cell lymphoma, with positive stains for CD20, PAX5, CD10, BCL6, and Mum-1. Fluorescence in situ hybridization (FISH) revealed an abnormality of BCL2/18q (16%). A staging positron emission tomography (PET) scan showed a large mediastinal mass involving the right pericardium, focal uptake in the left thyroid lobe, left skull base, and musculature around the proximal left femur. Chemotherapy was initiated with R-mini-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone). PET scans after three cycles of chemotherapy showed a complete metabolic response with the resolution of previously noted hypermetabolic lesions. The patient completed all six cycles of chemotherapy without issues. The differential diagnosis of a right atrial cardiac mass should include lymphoma. TTE is usually the initial imaging test, and a tissue biopsy is required for a definitive diagnosis. DLBCL is highly aggressive and carries a poor prognosis if untreated. Early diagnosis and treatment with standard chemotherapy are crucial for favorable outcomes.