A FISHY CASE: ECTOPIC PANCREATIC TISSUE CONTAINING A MUCINOUS CYSTIC NEOPLASM WITHIN THE DUODENUM IDENTIFIED BY "FISH-MOUTH" APPEARANCE ON ENDOSCOPY

Introduction:
Ectopic pancreatic tissue has been identified in various sites in the literature, including the stomach (most common) and small bowel. This ectopic tissue can be complicated by pancreatitis, cyst formation, and malignancy. A recent systematic review has evaluated 13 prior cases of intraductal pancreatic mucinous neoplasm within ectopic pancreatic tissue, including only one case seen within the duodenum¹. Here, we report another very rare case of intraductal pancreatic mucinous neoplasm (IPMN) arising from ectopic pancreatic tissue within the duodenum.
Case report:
A 64-year-old female, with no history of pancreatitis or tobacco use, was referred to our center for evaluation of a lesion seen on computed tomography (CT) imaging. The CT had showed a 2.6 x 1.5 cm soft tissue mass with attenuation similar to pancreatic parenchyma. It was adjacent to the pancreatic head and posterior and inferior to the duodenal bulb (Figure 1). Endoscopic ultrasound (EUS) was performed, and an intramural (subepithelial) lesion with central umbilication, “fish-mouth appearance”, and yellow mucous expression was found in the duodenal bulb (Figure 2A/2B). Outer margins were well defined on EUS. The lesion was anechoic, heterogenous, multicystic, and appeared to originate within the muscularis propria (Figure 2C). It measured 15 mm x 14 mm in size. Fine needle aspiration was performed, and 1 mL of clear and viscous fluid was collected. Fluid studies yielded: CEA 1.8 ng/mL, amylase 47 IU/L, glucose <10 mg/dL. Cytology showed bland mucinous epithelium with no dysplasia or carcinoma. Although the CEA level was low (possibly due to small volume aspirate), the cytology, low glucose levels, and presence of mucin were all most consistent with IPMN within aberrant pancreatic tissue in the duodenum. These findings, combined with EUS findings, were consistent with ectopic IPMN. Surveillance with MRI and EUS in 6 months was recommended by surgical oncology.
Discussion:
This rare case highlights unique endosonographic findings of aberrant pancreatic tissue containing IPMN. Given the small and stable size of the lesion over a 6 month period, this patient is undergoing continued imaging and endoscopic surveillance rather than surgical resection. Endoscopists should be aware of the key features that help characterize these lesions and know when to refer to a specialist center. With the increased use of EUS at other centers, further studies can help guide surveillance modalities and intervals for these ectopic pancreatic lesions.
References:
1. Kimura J, Okabayashi T, Sui K, et al. Clinicopathological features of intraductal papillary mucinous neoplasm derived from ectopic pancreas: A systematic review. Surg Open Sci. 2022;8:62-68. Published 2022 Mar 15. doi:10.1016/j.sopen.2022.03.001