Abstract
The patient was a 60-year-old man without any particular complaints, but he underwent abdominal computed tomography (CT) and magnetic resonance cholangiopancreatography (MRCP) due to a fatty liver, which revealed two similar cystic lesions regarded as branch duct-type intraductal papillary mucinous neoplasm (BD-IPMN) in the pancreatic body [BD-IPMN (b), 16 mm in size] and tail [BD-IPMN (t), 13 mm in size] without a “high-risk stigmata” or “worrisome features”. He subsequently received follow-up by MRCP every 6 months. Two years later, MRCP showed prominent dilation of the main pancreatic duct (MPD) and mural nodule formation within the dilated MPD adjacent to the BD-IPMN (b). Distal pancreatectomy specimens revealed that the BD-IPMN (b) was lined by low-papillary gastric mucinous epithelium with low-to-intermediate-grade dysplasia and involved the MPD, forming a malignant mural nodule showing pancreatobiliary-type IPMN. In contrast, the BD-IPMN (t) was lined by flat, monolayer columnar gastric mucinous epithelium without atypia, which suggested the possibility of a “simple mucinous cyst”. A genetic analysis showed KRAS mutation only in BD-IPMN (b). Differences in the histological and genetic findings between two similar BD-IPMNs in the present case may suggest what kinds of examinations should be performed in patients with BD-IPMNs without any worrisome features.
Highlights
Intraductal papillary mucinous neoplasm (IPMN) has variable malignant potential, ranging from premalignant intraductal lesions to malignant neoplasms with invasive carcinoma
We must address the relationship between the pre-existing branch ducttype intraductal papillary mucinous neoplasm (BD-IPMN) (b) and main duct (MD)-IPMN with mural nodule complicated after 2 years—whether MD-IPMN was merely concomitant and located nearby or had continuously developed from the branch duct (BD)-IPMN (b)
The communication between the BD-IPMN (b) and main pancreatic duct (MPD) was not clear on the initial images, but the sequential progression from the BD-IPMN (b) to MD-IPMN seems to be more likely than concomitant development for the following reasons: (1) resected specimens revealed totally sequential spread between the BD-IPMN (b) and MD
Summary
Intraductal papillary mucinous neoplasm (IPMN) has variable malignant potential, ranging from premalignant intraductal lesions to malignant neoplasms with invasive carcinoma. We report a surgically resected case of two small, low-risk BD-IPMNs, one of which involved the MPD and formed a malignant mural nodule and the other which was almost stable except for cyst enlargement during 2 years of follow-up. After 2 years, MRCP showed an enlargement (16–21 mm) of the BD-IPMN of the body [BD-IPMN (b)] and a prominent dilation of the adjacent MPD measuring 5 mm (Fig. 1b). The BD-IPMN (b) was lined by tall columnar epithelium with oval nuclei and clear mucinous cytoplasm showing flat to papillary configurations with mild epithelial stratification and low to intermediate cellular dysplasia (Fig. 3d). A genetic analysis showed no mutations of KRAS or GNAS
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