What are the microscopic findings of left atrial myxoma, including the cells involved?

Microscopic Findings of Left Atrial Myxoma

Left atrial myxomas are characterized microscopically by polygonal to stellate-shaped myxoma cells (lepidic cells) with abundant eosinophilic cytoplasm embedded within a loose, gelatinous myxoid stroma rich in acid mucopolysaccharides. 1, 2

Cellular Components

Myxoma Cells (Lepidic Cells)

• Polygonal to stellate-shaped cells with abundant eosinophilic cytoplasm arranged singly or in small clusters within the myxoid matrix 1, 2
• These cells are active cells of endothelial origin based on electron microscopic studies 3
• The cells are sparse and distributed throughout an extensive mucoid stroma 4

Stromal Cells

• Spindle-shaped cells embedded within the abundant myxoid matrix 2
• These cells contribute to the structural framework of the tumor 2

Endothelial Cells

• Line the vascular channels within the tumor 2
• Partially cover the tumor surface along with myxoma cells 5

Extracellular Matrix and Stroma

Myxoid Matrix Characteristics

• Abundant loose, gelatinous extracellular matrix that appears basophilic on H&E staining 1, 2
• Rich in acid mucopolysaccharides, specifically hyaluronic acid and chondroitin sulfate 1
• This mucopolysaccharide-rich spongiosa creates the characteristic myxomatous appearance 6

Vascular Elements

Blood Vessel Architecture

• Thin-walled blood vessels of varying caliber scattered throughout the tumor 1, 2
• Highly vascularized areas within the myxoid stroma 7
• Occasional thrombosis within tumor vessels 1

Hemorrhagic Features

• Hemorrhage and hemosiderin deposition are common findings, especially in larger tumors 1, 2
• These features reflect the friable nature of the tumor vasculature 4

Surface Characteristics

Surface Architecture

• Friable, gelatinous surface with adherent thrombus that serves as a source of embolic potential 2, 4
• Villous or papillary surface architecture in some cases, which is associated with higher embolic risk and greater embolic potential 1, 2
• Surface partially covered by myxoma cells and partly by endothelial cells 5

Immunohistochemical Profile

Positive Markers

• Vimentin (consistently positive) 2
• Calretinin (positive) 2
• PGP 9.5 (positive in 75% of cases) 5
• S100 antigen (positive in 67% of cases) 5
• Neurone specific enolase (NSE) (positive in 50% of cases) 5

Negative Markers

• Cytokeratin (negative) 2
• S100 (negative in standard panels, though some studies show variable positivity) 2

Important Clinical Correlations

Embolic Potential

• The friable surface with adherent thrombus creates a 25% overall embolism rate in untreated patients 1, 2
• More villous tumor morphology indicates greater embolic potential and urgency for surgical intervention 1

Histologic Distinction

• These microscopic features are histologically and histochemically different from left atrial thrombi, which is critical for accurate diagnosis 3
• The presence of abundant basophil cell infiltration and pericellular type IV collagen creates appearances similar to nerve sheath tumors (neurofibromas) 5