[A case of mucinous cystadenoma of the pancreas resected after a 10-year follow-up].

A 40-year-old woman was hospitalized because of acute pancreatitis. CT showed a monolocular cyst thought to be a pseudocyst. The patient was followed as an outpatient. The size of the cyst decreased 6 years later. Ultrasonography 10 years later demonstrated an enlarged cyst with a cyst-in-cyst formation. A tendency to increase in size and the irregular wall thickening indicated that the cyst was a malignant mucinous cystic neoplasm (MCN) and distal pancreatectomy was performed. The tumor was diagnosed histologically as a mucinous cystadenoma. A case of MCN resected after long-term follow-up is extremely rare. The present case is thought to be important for elucidation of the natural history of MCNs.