Primary non-Hodgkin's lymphoma of the right atrium presenting as a cardiac mass: surgical debulking followed by chemotherapy.

Primary cardiac lymphoma (PCL) is a rare malignancy, representing less than 1% of primary cardiac tumors. While benign tumors like myxomas more commonly affect the left atrium, malignant lesions-particularly lymphomas and angiosarcomas-typically involve the right atrium. The nonspecific presentation often delays diagnosis and treatment. A 40-year-old male presented with progressive dyspnea, chest pain, fatigue, and pedal edema. Transthoracic and transesophageal echocardiography revealed a large right atrial mass with pericardial effusion. Cardiac magnetic resonance imaging (MRI) showed a heterogeneous mass with peripheral enhancement and central necrosis, initially suggestive of angiosarcoma. Due to inconclusive biopsy findings, the patient underwent surgical debulking. Histopathological analysis confirmed diffuse large B-cell lymphoma (DLBCL) (non-germinal center type) with CD20 positivity and a high Ki-67 index. Postoperative positron emission tomography (PET) scan showed residual mediastinal involvement. The patient received six cycles of R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, prednisone) chemotherapy with intrathecal methotrexate. Follow-up positron emission tomography-computed tomography (PET CT) demonstrated complete metabolic remission, corroborated by echocardiography. This case underscores the importance of including PCL in the differential diagnosis of right atrial masses. Early imaging, prompt tissue diagnosis, and chemotherapy can lead to excellent outcomes even in aggressive disease presentations.