Sections demonstrate markedly ectatic venous channels characterized by large, blood-filled lumina lined by a single layer of flattened, cytologically bland endothelial cells. The vessel walls show variable thickness with well-developed smooth muscle layers and focal intimal fibrosis. Luminal contents include stagnant blood and foci of organizing thrombus. The surrounding periarticular soft tissue/synovium shows extravasated erythrocytes and scattered hemosiderin-laden macrophages. No evidence of endothelial multilayering, cytologic atypia, or infiltrative growth is identified.
Excision biopsy from Achilles joint.
Soft tissue fragments collectively measured 4.2x1.5x0.8 cm, totally embedded.
Achilles joint lesion, excision biopsy: