What is the diagnosis and cause of fainting episodes in a patient with a small, circumscribed round mass in the left atrium?

Diagnosis and Management of Left Atrial Mass with Syncope

A. Diagnosis: Left Atrial Myxoma

The diagnosis is left atrial myxoma, the most common primary cardiac tumor, accounting for approximately 50% of all benign cardiac neoplasms. 1, 2

• Myxomas occur most frequently in the left atrium, typically attached to the interatrial septum 1
• They are most common in patients between the 4th and 6th decade of life, with female predominance 3
• The tumor appears as a small, circumscribed round mass on imaging (CT and echocardiography) 4, 5
• Cardiac myxomas have an incidence of 0.02% in autopsy series 1, 2

B. Mechanism of Fainting Episodes

The syncope results from mechanical obstruction of blood flow across the mitral valve during diastole, causing transient reduction in cardiac output and cerebral hypoperfusion. 1, 6, 5

Primary Mechanism: Obstructive "Ball-Valve" Effect

• The mobile tumor prollapses into the mitral valve orifice during diastole, causing dynamic flow obstruction 5, 7
• This intermittent obstruction reduces left ventricular filling and cardiac output, leading to cerebral hypoperfusion and loss of consciousness 1, 4
• Syncope is particularly common with positional changes or exertion when hemodynamic demands increase 4, 8

Additional Contributing Mechanisms

• Cardiac arrhythmias (including symptomatic bradycardia) can occur due to tumor proximity to the conduction system 5
• The tumor may cause reflex vagal responses leading to vasovagal-type syncope 6
• Larger myxomas (>6 cm) are associated with worse prognosis and more severe obstructive symptoms 3, 4

C. Microscopic Findings of Cardiac Myxoma

Cellular Components

Myxoma cells (lepidic cells):

• Polygonal to stellate-shaped cells with abundant eosinophilic cytoplasm
• Round to oval nuclei with fine chromatin
• Cells arranged singly or in small clusters within myxoid stroma 2

Stromal characteristics:

• Abundant myxoid (mucopolysaccharide-rich) extracellular matrix
• Loose, gelatinous appearance with basophilic staining
• Rich in acid mucopolysaccharides (hyaluronic acid and chondroitin sulfate)

Vascular elements:

• Thin-walled blood vessels of varying caliber
• Hemorrhage and hemosiderin deposition common
• Occasional thrombosis within tumor vessels

Additional features:

• Inflammatory cells (lymphocytes, plasma cells, macrophages) scattered throughout
• Calcification may be present, especially in older lesions
• Surface endothelial lining when attached to endocardium
• Glandular structures occasionally present (rare)

Histologic Pattern

• The cells are embedded in a loose myxoid stroma creating a characteristic "stellate" appearance
• Perivascular condensation of tumor cells is typical
• Surface may show fibrin deposition and thrombus formation (source of embolic risk) 1

Management Recommendations

Surgical excision is the definitive and only established treatment for cardiac myxoma and should be performed urgently to prevent life-threatening complications. 1, 2, 6

Surgical Indications (Class I)

• All symptomatic left atrial myxomas require surgical resection 1, 2
• Surgical excision reduces stroke risk compared to conservative management 1
• The overall embolism rate is 25% in untreated patients, with 30-40% of myxomas causing embolic events 1

Pre-operative Considerations

• Echocardiography (transthoracic and transesophageal) is the diagnostic technique of choice 2
• Cardiac MRI or CT provides additional characterization for surgical planning 2
• More villous tumor morphology indicates greater embolic potential and urgency for surgery 1

Post-operative Outcomes

• Surgical removal results in resolution of obstructive symptoms including syncope 5
• Arrhythmias (including bradycardia) typically resolve after tumor excision 5
• Prognosis is excellent with complete surgical resection 8

Critical Pitfalls to Avoid

• Do not delay surgery once diagnosis is established—risk of sudden death from complete mitral obstruction or massive embolism 4
• Do not perform pericardiocentesis if pericardial effusion is present, as this may worsen hemodynamics 1
• Avoid anticoagulation alone as definitive therapy—it does not address the mechanical obstruction and may increase bleeding risk 1