Case Report: Primary Cardiac Angiosarcoma of the Right Atrium Initially Misdiagnosed as Myxoma

BACKGROUND: Primary cardiac angiosarcoma (PCAS) is an extremely rare and highly aggressive malignant tumor, accounting for ~30% of primary cardiac sarcomas. It predominantly arises in the right atrium with non-specific symptoms, leading to frequent misdiagnosis as myxomas or thrombi. Cases with an 8-year insidious course are exceptionally rare and diagnostically challenging. METHODS: A 54-year-old female with 8-year intermittent chest tightness acutely worsened for 1 day was evaluated. Diagnostic workup included transthoracic echocardiography (TTE), computed tomography (CT), and laboratory tests. The patient underwent surgical resection under cardiopulmonary bypass, followed by histopathological confirmation. RESULTS: Initial TTE suggested right atrial thrombus, while repeat TTE favored myxoma. CT confirmed a large right atrial mass with moderate pericardial effusion; multiple small pulmonary nodules were assessed as low-risk lesions with no evidence of distant metastasis. Intraoperatively, a 5.0 × 6.0 cm mass was densely adherent to the right atrial wall. Histopathology and immunohistochemistry (CD31+, CD34+, Factor VIII+, Ki-67 40%) confirmed angiosarcoma. The patient recovered uneventfully and was referred for adjuvant chemotherapy. CONCLUSIONS: PCAS has an insidious course and is easily misdiagnosed by conventional imaging. Early complete surgical resection remains the mainstay of treatment. A high index of suspicion for malignancy is essential in all patients with right atrial masses.