RESUMO
Accumulation of free fluid in the peritoneal cavity is called ascites. The first step in identifying its etiology is to determine the serum-ascites albumin gradient [SAAG]. According to this parameter, a high SAAG is regarded as a gradient greater than 1.1 g/dL. This condition has some differential diagnoses such as liver cirrhosis, Budd-Chiari syndrome, heart failure, and idiopathic portal fibrosis. In the present article, we present a young man with abdominal distention due to a high SAAG. Further evaluation of the abdominal and thoracic cavity revealed a mass in the posterior mediastinum, which had compressed the inferior vena cava and left atrium and led to Budd-Chiari syndrome. Evaluation of the biopsy sample showed fibrosarcoma. Mediastinal fibrosarcomas, though rare, should be considered in the differential diagnosis of mediastinal masses