A case of ectopic pancreas of the stomach accompanied by intraductal papillary mucinous neoplasm with GNAS mutation

Abstract

Background: Ectopic pancreas is basically a benign disease and is not always necessary to be removed. However, all types of neoplasms occurring in the normal pancreas such as ductal adenocarcinomas and intraductal papillary mucinous neoplasms (IPMNs) may develop even within ectopic pancreas. We recently encountered an extremely rare case of ectopic pancreas in the gastric antrum associated with IPMN possessing a GNAS mutation.

Case presentation: A 71-year-old Japanese woman complained of epigastric pain. Computed tomography and upper gastrointestinal endoscopy showed an intramural cystic mass in the antrum of the stomach. Endoscopic ultrasound-guided fine needle aspiration (EUS-FNA) biopsy did not give a definitive diagnosis, and the patient underwent resection of the lesion. Histology of the resected specimen showed that the gastric intramural lesion was ectopic pancreas. Moreover, the lesion contained dilated duct components with tubulo-villous epithelial proliferation consistent with pancreatic IPMN. Since the covering epithelial cells had highly atypical nuclei, the lesion was diagnosed as IPMN with high grade dysplasia. Immunohistochemistry showed that the IPMN component showed to be MUC2-, MUC5AC-, and CDX2-positive but MUC1- and MUC6-negative. Mutational analyses using genomic DNA revealed that the IPMN component had a mutation of GNAS at exon 8 (Arg201Cys).

Conclusion: We finally diagnosed this case as gastric ectopic pancreas accompanied by intestinal type IPMN with high grade dysplasia possessing GNAS mutation. Although there were 17 cases of ectopic pancreas with IPMN including 6 cases of gastric ones reported in the English literature, this is the first case of ectopic pancreas with IPMN which was proved to have GNAS mutation. Intimate preoperative examinations including imaging analyses and EUS-FNA biopsy/cytology are recommended to decide whether the lesion has to be resected or not even if they are not effective for getting the right diagnosis.

Keywords: Ectopic pancreas; GNAS mutation; Heterotopic pancreas; IPMN; Intraductal papillary mucinous neoplasm; Pancreatic heterotopia.

Fig. 1

Findings of CT and upper gastrointestinal endoscopy. Coronal section of CT revealed an intramural cystic lesion of the stomach (a). Upper gastrointestinal endoscopy showed an elevated lesion covered with normal mucosa in the gastric antrum (b). Arrows in a and b indicate the lesion

Fig. 2

Macroscopic findings of the resected stomach and cut surface of the sliced specimens. Resected stomach showed a flat elevated lesion in the antrum (a). Cut surface of the specimens longitudinally sliced at the central portion of the lesion appeared to be solid but not cystic (b). Arrows in (a) and (b) indicate the lesion

Fig. 3

Histological and immunohistochemical findings of the gastric intramural lesion. Low and medium power views of the specimen showed that the lesion was ectopic pancreas located mainly in the proper muscular and subserosal layers (a, b). Dilated duct components with tubulo-villous epithelial proliferation at the deep portion of the lesion were consistent with pancreatic IPMN (c). The covering epithelial cells were MUC2- (d), MUC5AC- (e), and CDX2-positive (f). b, c High-power images of insets b and c in a

Fig. 4

Mutational analysis of GNAS gene using genomic DNA extracted from histological specimen. IPMN component associated with ectopic pancreas had a heterozygous mutation of GNAS gene at codon 201 in exon 8 (Arg201Cys)