RADIOLOGY: PANCREAS: Case# 32824: PANCREATIC PSEUDOCYST. The patient is a 45 year old male with a history of pancreatitis. He now presents with increasing abdominal pain. CT Findings: A large pancreatic pseudocyst measuring 21 x 14 x 24 cm is present in the LUQ situated between the stomach and spleen. The stomach is compressed and displaced medially by the pseudocyst. MR Findings: There is a large (16cm) heterogeneous fluid collection centered in the left upper quadrant, markedly compressing the stomach. The residual pancreas is difficult to identify in the tail, body, and neck regions but a small portion is seen in the pancreatic head region. The fluid collection contains predominantly high signal fluid on T2 weighted sequences with several clumps of low signal debris. This most likely represents residual pancreatic necrosis. Pancreatic pseudocysts are usually the sequelae of pancreatitis, most often associated with the subacute or chronic varieties. Peripancreatic fluid collections in the setting of acute pancreatitis are not pseduocysts. A pseudocyst is a cystic structure with a thick, fibrous wall and is not lined with epithelium (hence, it is not a true cyst). A pseudocyst may have a persistent connection to the pancreatic duct which may be demonstrated by ERCP. Typically, an uncomplicated pseudocyst will have a homogeneous water density. Increased density or inhomogeneity indicate some complicating factor such as hemorrhage or infection. Psuedocysts may also form in the walls of bowel (stomach, duodenum, colon) due to extension of pancreatic enzymes into the surrounding tissues.