A 17-year-old adolescent boy presented with a history of epigastric pain for the past 10 to 12 weeks. He had no significant family or personal medical history. The results of a physical examination were nonrevealing, therefore an esophagogastroduodenoscopy was performed. When the endoscope was introduced into the stomach, a 1-cm polypoidal lesion was seen in the gastric antrum. The lesion appeared to be submucosal with an intact submucosa and muscularis propria interface. No lymphadenopathy was seen. This lesion in the gastric antrum was excised and sent for histopathologic examination.

On microscopic examination, a well-circumscribed submucosal nodular lesion with overlying benign gastric mucosa was evident (Figure 1). The lesion displayed unremarkable pancreatic lobules with acini, ducts (Figure 2), and islets of Langerhans cells (Figure 3, arrow). No evidence of cellular pleomorphism, necrosis, mitosis, or stromal reaction was present.

Heterotopic pancreas is defined as pancreatic tissue outside the boundaries of the pancreas that lacks anatomic and vascular continuity to this organ. Heterotopic pancreas is a relatively infrequent lesion, with an incidence ranging from 0.5% to 13% in autopsy studies. Heterotopic pancreas is usually found in the upper gastrointestinal tract, with more than 90% of the cases involving the stomach, duodenum, jejunum, and Meckel diverticulum.1 Unusual locations are the colon, spleen, liver, biliary tract, mesentry, skin, lymph nodes, and fallopian tube.

The pathogenesis of this lesion is unknown; it is believed to arise during embryonic development of the gastrointestinal tract. The normal pancreas is derived from several evaginations originating from the wall of the primitive duodenum. During embryogenesis, if one or more evaginations remain in the wall of the bowel, then it may be carried away from the remainder of the gland by the developing gastrointestinal tract and may give rise to heterotopic pancreas.2 The other theory proposes pancreatic metaplasia of endodermal tissues that end up in the submucosa during embryonic life.

Pancreatic heterotopia grossly resembles normal pancreatic parenchyma as a submucosal nodule, as an intramural mass, or as a nodular lesion involving the serosa. On gross examination, the color is yellow to yellow-white, and cut section reveals a lobulated appearance. The size of the nodule varies from 0.2 to 4.0 cm. Histologically, it contains any mixture of tissues that may be found in the normal pancreas but usually consists primarily of ducts and surrounding simple mucin-producing glands. Heterotopic pancreas can be divided into 4 types: type I, those comprising all cell types (total heterotopia); type II, composed of ducts only (canalicular heterotopia); type III, composed of acinar cells only (exocrine heterotopia); and type IV, composed of islet cells only (endocrine heterotopia).3 

The majority of the patients are asymptomatic and the lesion is diagnosed incidentally on autopsy. This lesion may be mistaken endoscopically for mucosal polyps, and the diagnosis is usually unexpected by the gastroenterologist. Some patients present with gastric pain, bleeding, nausea, vomiting, and chest pain. Although rare, diseases like pancreatitis, pancreatic cysts, islet cell tumor, and adenocarcinoma can arise within heterotopic pancreas. Because heterotopic pancreas can present as a mass lesion, it is important for surgical pathologists to recognize this lesion on frozen sections.

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Author notes

Reprints: Vishal S. Chandan, MD, Department of Pathology, State University of New York, Syracuse, Upstate Medical University, 750 E Adams St, Syracuse, NY 13210 ([email protected])