Leiomyosarcoma of the left atrium mimicking a left atrial myxoma

Unlike benign neoplasms, primary cardiac malignancies are rarely intracavitary and, when located in the left atrium, may mimic myxoma on cardiac imaging. Cardiac surgeons should be alerted to ask for prompt surgical pathologic study in any case of intracavitary cardiac mass. A 21-year-old woman was admitted to the hospital with pulmonary edema and shock. Transthoracic echocardiography showed a large (4 × 7-cm) mobile mass within the left atrium obstructing the mitral valve orifice during diastole. The diagnosis of left atrial myxoma was put forward, and an emergency operation was performed with the patient on cardiopulmonary bypass. The left atrium was approached via an extended transseptal incision. The left atrium was occupied by a whitish mass, and the tumor appeared entrapped in the mitral orifice without infiltration of the leaflets or the annulus. The mass originated from the roof of the left atrium, between the pulmonary veins. The tumor and the underlying endocardium were smoothly dissected from the myocardium of the atrial wall, which appeared soft and without evidence of invasion. The operation was performed without complications. At gross examination, the mass appeared whitish and ovoid. It measured 7 × 3 × 3.5 cm and weighed 51 g. The surface was slightly irregular and wrinked, hard to cut with a knife. Accessory clusters of small round masses were also present. Microscopic examination of histologic sections revealed a storiform proliferation with pleomorphic cells enmeshed in a myxoid extracellular matrix with a high mitotic index. Necrotic foci and lymphocytic-plasmacellular infiltrates were also observed. At immunohistochemistry, the neoplastic cells appeared vimentin, desmin, and α-smooth muscle actin positive and myogenin negative, in keeping with a pleomorphic leiomyosarcoma. The patient was treated with anthracycline-based chemotherapy (doxorubicin plus fosfamide plus cisplatin alternated with fosfamide plus cisplatin every 15 days for 2 months). Eleven months later, the patient underwent reoperation for suspected recurrence of the tumor on the anterior mediastinum, but the removed mass turned out to be a reactive hyperplasia of the thymus secondary to chemotherapy. At 24 months from surgical resection, the patient is well, without evidence of local recurrence or metastases on computed axial tomography.