A heterogeneous pedunculated mass is located in the left atrium of a young adult. What is the most likely diagnosis?

• A. Lipoma
• B. Fibroma
• C. Thrombus
• D. Myxoma

Answer: (D)

Left atrial myxoma is the classic diagnosis when you encounter a pedunculated, heterogeneous mass in the chamber of a young adult. These tumors are the most common primary cardiac tumor in adults and typically arise from the atrial septum near the fossa ovalis. The pedunculated, mobile nature explains how it can intermittently obstruct the mitral valve or shed emboli, producing symptoms like dyspnea or chest events. The heterogeneous gross appearance reflects the gelatinous, mucopolysaccharide-rich stroma with variable areas of hemorrhage or calcification that characterizes myxomas.

Less fitting would be a lipoma, which tends to be a uniform, well-circumscribed, often encapsulated mass and not usually a mobile, stalked lesion. A fibrous tumor (fibroma) generally occurs in children and is intramural, not a pedunculated left atrial mass. A thrombus would be more tied to conditions causing stasis or arrhythmias and is less likely to present as a mobile, stalked mass in a young person without such risk factors.