Retroperitoneal and mediastinal pancreatic pseudocyst accompanied by pancreas divisum

A 68-year-old man with a history of alcoholism was seen in the clinic for dyspnea on exertion. Chest X-ray showed a large right pleural effusion. He was admitted to our hospital. Amylase level in the effusion was elevated, and plain CT demonstrated a retroperitoneal and mediastinal low density area and multiple calcifications in the pancreas. Enhanced CT after drainage of the pleural effusion revealed that the low density area was a cystic lesion, and the lesion grew to a large size. A cluster of small pancreatic pseudocysts in the pancreatic tail and body were noted. We diagnosed a pancreatic pseudocyst of the mediastinum and retroperitoneum, and pancreatic pleural effusion secondary to chronic pancreatitis. An internal fistula between the pancreatic pseudocysts and the cystic lesions in the retroperitoneal space was suspected by MRCP. The fistula was not recognized by ERCP because of pancreas divisum. Distal pancreatosplenectomy was performed and the mediastinal pancreatic pseudocyst disappeared on CT four months postoperatively. MRCP was an effective tool to diagnose an internal fistula in a patient with pancreas divisum.