Mesothelial cyst of the pericardium, absent on earlier computed tomography.

Pericardial cysts are benign intrathoracic lesions that are considered to be congenital. They are usually found incidentally upon chest radiography and typically cause few symptoms. Their true incidence is unknown. Herein, we describe the case of a 41-year-old man who, over nearly a decade, had undergone frequent hospital admissions for fever and thoracic pain. Computed tomography had shown no evidence of any intrathoracic mass. He was admitted to the hospital with fever, chest pain, tachycardia, dyspnea, and cough. The symptoms persisted despite medical therapy. Computed tomography revealed a pericardial cyst on the right side of the anterior mediastinum, near the confluence of the brachiocephalic vein and the superior vena cava and very close to the ascending aorta. The mass compressed the right main bronchus. Due to the cyst's unusual location and the ineffectiveness of medical therapy, we excised the tumor via median sternotomy. We found a large (7 x 4-cm), well-circumscribed, unilocular cyst, which unexpectedly involved the outside pericardial surface and the phrenic nerve. Histopathologic examination confirmed that the lesion was a simple mesothelial cyst of the pericardium. After the surgery, the patient's fever and chest pain resolved. We know of no other report of a pericardial cyst that had gone undetected upon earlier computed tomography. We believe that surgical treatment of pericardial cysts should be reserved for patients who have severe symptoms due to complications, or when diagnosis is uncertain and malignancy is suspected.