What is the definition and pathophysiology of a left atrial myxoma?

Left Atrial Myxoma: Definition and Pathophysiology

Definition

Left atrial myxoma is the most common primary benign cardiac tumor, accounting for approximately 50% of all benign cardiac neoplasms, with an incidence of 0.02% in autopsy series. 1, 2

• Myxomas are benign neoplasms that arise from primitive multipotent mesenchymal cells in the endocardium 3
• Approximately 90% occur sporadically, while 10% have a familial autosomal dominant inheritance pattern, often as part of Carney complex 3
• The tumor most frequently originates in the left atrium, typically attached to the interatrial septum at the fossa ovalis region 1, 2

Pathophysiology

Cellular Origin and Microscopic Architecture

The tumor develops from undifferentiated mesenchymal cells with characteristic histologic features that define its behavior and embolic potential. 3

• Cellular components include myxoma cells (lepidic cells) that are polygonal to stellate-shaped with eosinophilic cytoplasm, arranged singly or in small clusters 2
• Stromal characteristics consist of abundant loose, gelatinous myxoid matrix rich in mucopolysaccharides (hyaluronic acid and chondroitin sulfate) that appears basophilic on H&E staining 1, 2
• Vascular elements include thin-walled blood vessels of varying caliber scattered throughout, with frequent hemorrhage and hemosiderin deposition 1, 2
• Surface architecture may be villous or papillary, which correlates directly with higher embolic risk due to friable surfaces that readily generate thrombus or tumor fragments 1, 3

Three Principal Pathophysiologic Mechanisms

The clinical manifestations of left atrial myxoma result from three distinct mechanisms that determine symptom severity and urgency of intervention. 1

1. Mechanical Obstruction

• The tumor causes intermittent obstruction of blood flow across the mitral valve during diastole 1, 2
• This reduces left ventricular filling and cardiac output, leading to cerebral hypoperfusion 2
• Results in syncope, heart failure symptoms, or sudden death 1
• May trigger reflex vagal responses causing vasovagal-type syncope 2

2. Embolic Complications

• The overall embolism rate is 25% in untreated patients, with embolic stroke being the presenting symptom in up to 50% of cases 1, 2
• Ischemic stroke results from either embolization of thrombus that forms on the tumor surface or direct embolization of tumor fragments 1
• Villous or papillary surface morphology indicates greater embolic potential and urgency for surgery 2

3. Constitutional Symptoms

• Fever and weight loss occur, likely mediated by cytokine release from the tumor 1

Clinical Pitfalls and Important Distinctions

• Familial cases present at younger ages, involve multiple cardiac chambers simultaneously, and have significantly higher recurrence rates (up to 20%) compared to sporadic cases (1-5%) 3
• Anticoagulation or antiplatelet therapy alone is inadequate and does not prevent embolic complications—surgical excision is the only definitive treatment 1, 2
• The tumor's mobility and size determine the severity of mechanical obstruction and embolic risk 4