High-grade left atrial intimal sarcoma mimicking myxoma: The diagnostic and therapeutic relevance of tumor topography.

Primary cardiac tumors are rare; among them, sarcomas represent an aggressive minority with complex diagnosis and poor prognosis. We report the case of a 45-year-old woman with a history of dysautonomia who presented with progressive dyspnea (New York Heart Association class II-III) and exertional angina. Transthoracic echocardiography revealed a 38 × 27 mm mobile mass in the left atrium, attached to the posterior wall, partially obstructing the mitral inflow tract. A presumptive diagnosis of myxoma was made.Intraoperatively, a 5 × 5 cm fibrolipomatous mass infiltrating the posterior atrial wall and pulmonary veins was resected, and structural reconstruction was performed with autologous and bovine pericardial patches. Histopathology showed a high-grade intimal sarcoma, MDM2 and vimentin positive, with a Ki-67 index of 50%.Postoperatively, the patient developed persistent sinus node dysfunction requiring permanent pacemaker implantation, and refractory bilateral pleural effusion managed with thoracic drainage. Positron emission tomography-computed tomography showed no metastatic disease but revealed bilateral jugular thrombosis and hepatic congestion. She began chemotherapy (doxorubicin/ifosfamide), but experienced rapid local recurrence and new hepatic metastases. She began second-line therapy with progressive disease.This case emphasizes the importance of tumor origin. A posterior infiltrative mass suggests malignancy, and preoperative recognition of this pattern may guide surgical planning and oncologic intervention. Learning objective: This case underscores the importance of correctly identifying intimal sarcomas, often misdiagnosed as undifferentiated pleomorphic sarcomas, to ensure accurate prognosis and management. It demonstrates the diagnostic utility of MDM2 and vimentin, and the value of imaging in suggesting malignancy based on tumor topography-specifically, when arising from the posterior left atrial wall. Recognizing these patterns may help avoid misclassification and guide timely surgical and oncologic decisions.