Mucinous Non-neoplastic Cyst of the Pancreas
A 69-year-old woman was admitted to our hospital for evaluation of an asymptomatic cystic mass of the pancreas detected incidentally during a health checkup. The patient did not have a history of smoking or alcohol abuse. The serum amylase level was 60 IU/L (normal range, 54 to 168 IU/L), lipase level was 39 IU/L (normal range, 15 to 60 IU/L), and clinical signs suggesting pancreatitis were not observed. Routine laboratory values, including tumor markers and serological tests for hepatitis B and hepatitis C virus, were negative. Contrast-enhanced abdominal computed tomography demonstrated a multilocular low density cystic lesion measuring approximately 3.0 cm in the tail of the pancreas. The diameter of the main pancreatic duct was normal, and there was no evidence of an enhanced solid portion. Three-dimensional magnetic resonance cholangiopancreatography imaging revealed a multilocular cystic mass in the pancreatic tail with multiple cysts in the head and body of the pancreas (). Surgical exploration revealed a 3×2.5 cm-sized, multilocular cyst in the tail of the pancreas. The lesion consisted of variable-sized (0.3-1.5 cm) multiple macrocysts separated by thin septa. Mucinous material was observed in several cysts. There was no communication with the main or large branch pancreatic ducts (). The cysts were lined by a monolayer of cuboidal to columnar epithelial cells with focal pseudostratification (). The cyst walls consisted of paucicellular fibrous tissue. There was no ovarian-like stroma in the cyst walls. There was no evidence of nuclear pleomorphism or mitotic figure, suggesting a malignant tumor. The remaining pancreatic tissue was histologically unremarkable. Immunohistochemically, the duct lining epithelial cells were diffusely strongly positive for keratin 7, 19, and Muc6 and showed weak Muc1 expression, whereas the cells were negative for Muc2 and Muc5Ac (, inset). On the basis of histological and immunohistochemical findings, a final diagnosis of MNCP was made.