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

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.

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.

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.

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.