Abstract
Chronic expanding hematoma (CEH) is a rare condition characterized by a slowly enlarging hematoma. While chronic expanding hematomas can occur following trauma or surgery, their idiopathic presentation is exceedingly rare. An expanding hematoma can silently lead to diastolic cardiac dysfunction. A 69-year-old woman without a history of thoracic surgery or chest trauma presented with an incidentally discovered pericardial mass measuring 90 × 60 × 45 mm. Imaging revealed a mass with a calcified capsule that compressed the right heart in the anterior mediastinum. Despite initial attempts at off-pump resection, the procedure was converted to on-pump resection because of cardiac injury caused by extensive adhesions. The excised specimen was encapsulated and filled with an old hematoma. Histopathological examination results confirmed the diagnosis of chronic expanding hematoma with no evidence of malignancy. Despite being asymptomatic, the mass was significantly compressing the heart, necessitating surgical resection for diagnostic and therapeutic purposes.