Abstract Body (Do not enter title and authors here): Description of Case
A 40-year-old woman presented with a 3-month history of dyspnea. A murmur was found on examination. Echocardiography reported moderate mitral stenosis and regurgitation with diffuse thickening and calcification of the anterior mitral leaflet (Fig1.A), thought to be due to rheumatic disease. She had runs of supraventricular tachycardias not controlled with diltiazem. Her dyspnea progressively worsened; transesophageal echocardiography(TEE) showed severe mitral stenosis and mitral regurgitation (mean gradient 18 mmHg; Fig1.B) with a dense CW Doppler (Fig 1.C) and a mass on left atrial free wall. Cardiac MRI revealed diffuse left atrial thickening with delayed enhancement of the left atrium, left atrial appendage, and extending into the right upper and left inferior pulmonary veins. The mass was initially suspected to be a thrombus. She was placed on rivaroxaban and scheduled to undergo mitral valve replacement.
When she presented to our emergency department with dizziness she was found to have paroxysmal atrial fibrillation and pulmonary embolism. On admission she had an intermittent opening snap and a 1/6 mid-diastolic rumble with a 2/6 holosystolic murmur at the apex. Work-up for infectious disease and antiphospholipid syndrome was negative. NT-proBNP was mildly elevated. At surgery the mass invaded the mitral valve and the anterior, septal, and superior part of the left atrial lateral wall and could only be partially excised (Fig1.D). Pathology showed high-grade undifferentiated pleomorphic cardiac sarcoma .

Discussion
This case highlights the diagnostic challenges associated with primary cardiac tumors masquerading as valvular pathology. The presentation included dyspnea, typical auscultation of mitral stenosis and features of stenosis on echocardiography. Presumptive diagnoses included rheumatic heart disease, calcific degeneration, infective endocarditis, and autoimmune processes; the atrial mass was initially thought to be a thrombus. A thorough, multidisciplinary approach to diagnosis, utilizing multimodality imaging techniques and ultimately tissue biopsy were required to make the correct diagnosis. Maintaining a broad differential when dealing with valvular masses is key, since relying solely on imaging findings may not suffice for definitive tissue diagnosis.