Primary Atrial Undifferentiated Sarcoma Found on FDG PET/CT Mimicking Cardiac Myxoma.

A 52-year-old man had shortness of breath and chest discomfort for 2 months. Chest CT and MRI showed a mass in the left atrium attached to the mitral annulus without obvious enhancement. Initial diagnosis was suspected of myxoma. Preoperative FDG PET/CT demonstrated the corresponding lesion with abnormal FDG uptake, indicating a malignancy. Finally, histopathologic examination revealed primary undifferentiated sarcoma.