Abstract
A 73-year-old woman presented with a cystic lesion measuring 18mm in diameter in the pancreatic tail on plain CT. The cyst diameter had doubled in nine years. A Contrast-enhanced MRI showed a smooth and enhanced cyst-wall measuring 2mm in thickness, with Endoscopic Ultrasound (EUS) revealing a septal structure, but no mural nodules. The patient was followed without treatment because the cyst was small and no mural nodules were observed. However, the cyst size continued to increase, reaching 30mm × 35mm at 18 months. Thus, distal pancreatectomy was performed due to a suspected mucinous cystic neoplasm (MCN). A postoperative pathohistological examination revealed the cyst to be mostly lined with a monolayer of cuboidal mucinous-epithelium, but it was partly covered with a columnar mucinous-epithelium without atypia. Neither communication with the pancreatic duct nor ovarian-like stroma was identified, leading to a diagnosis of a simple mucinous cyst (SMC). It was difficult to distinguish this cystic mass as a SMC preoperatively because it mimicked MCN with an enhanced thick-wall and a septal structure, and had been increasing in size over time. SMCs have only recently been defined as a type of mucinous cystic lesion that should be differentiated from MCN. SMC should be considered as a possibility when diagnosing MCN-like pancreatic cysts.
