Pathophysiology
Clinical meaning
Atrial myxoma is the most common primary cardiac tumor, accounting for approximately 50% of all benign cardiac neoplasms in adults. These tumors arise from multipotent mesenchymal stem cells in the subendocardium and are composed of scattered stellate or polygonal myxoma cells (lipidic cells) embedded in an abundant mucopolysaccharide-rich stroma (myxoid matrix) with variable amounts of collagen, elastic fibers, and smooth muscle cells. The gross appearance is typically a pedunculated, gelatinous, lobulated mass attached to the interatrial septum at the fossa ovalis by a narrow stalk, though sessile and broad-based variants also occur. Approximately 75 to 80% of myxomas originate in the left atrium, 15 to 20% in the right atrium, and rarely in the ventricles. The left atrial location is clinically significant because the tumor prolapses through the mitral valve during diastole, creating intermittent mitral valve obstruction that mimics mitral stenosis. This ball-valve effect produces position-dependent symptoms: patients characteristically experience dyspnea, syncope, and dizziness that worsen with specific body positions (particularly sitting upright or leaning forward) and improve with lying down or position changes that shift the tumor away from...