Nonbacterial Thrombotic Endocarditis Presenting as a Mass in the Right Atrium Diagnosed by Open Chest Surgery: A Case Report.

Nonbacterial thrombotic endocarditis (NBTE) is a condition that results in the development of vegetation on cardiac valves that are devoid of inflammation and bacteria. We herein report a 60-year-old man who transferred to our hospital because of a systemic embolism and heart failure. A mass in the right atrium and vegetation on the mitral valve were observed. He was first diagnosed with infectious endocarditis according to the Duke criteria. During treatment, however, the patient was diagnosed with antiphospholipid syndrome and cancer. After four weeks of antibacterial therapy, the patient underwent open chest surgery, and the postoperative histological diagnosis was NBTE.