LAUSR

Introduction Simple mucinous cyst (SMC) of pancreas is a disease defined by the Baltimore Consensus in 2014. Pancreatic mucus-producing neoplasms are considered to be premalignant tumors, but SMC is not considered to have a risk of malignancy or recurrence. Presentation of case The case was a woman in her 50s with a chief complaint of abdominal pain. A blood exam showed an increase in the inflammatory response, and a slight increase of Amylase. CT showed a cystic lesion 80 mm in size at tail of the pancreas, and disproportionate fat stranding and ascites around it. We diagnosed peritonitis associated with the rupture of a cystic lesion accompanied by pancreatitis. Abdominal pain was improving, and we decided to proceed with the detailed examination. MRI showed a uniform hyper-intensity on T2WI, and a nodular-like hypo-intensity was observed inside, which was enhanced. During the follow-up, the lesion had gradually grown and re-ruptured. As we could not deny malignancy by image findings, distal pancreatectomy was performed. The intracystic fluid was browny and turbid, and Amylase, CEA and CA19-9 of the cystic fluid were elevated. We diagnosed it SMC by histopathological findings. Currently, she had no recurrence for 1 year. Discussion SMC is a type of true cysts, so rupture was rare. However, if the cyst wall becomes weak due to complications such as acute pancreatitis. It is probable that our case had pancreatitis and the cyst wall was weakened. Conclusion SMC detected by rupture was very rare, so we report this case.