—  SPECIALTY CONFERENCE  —

Gastrointestinal Pathology

Case 2 - Ectopic Pancreas

Barbara McKenna
University of Michigan
Ann Arbor, Michigan


Click on each slide thumbnail image for an enlarged view
Clinical History:
A 40-year-old woman presented with epigastric pain. CT scan of abdomen showed a small distal gastric mural nodule, suspicious for neoplasm. The patient underwent a partial gastrectomy. A 1.5 cm tan, well-circumscribed subserosal nodule was present on the distal gastric wall.


Case 2 - Figure 1 - A large pancreatic-type duct is surrounded by fibrous tissue in the muscular wall of the stomach.
Case 2 - Figure 2 - Lobular arrangements of mucous glands are also present between muscle bundles of the muscularis propria.


Case 2 - Figure 3 - Muscle tends to wrap around the glandular structures.
Case 2 - Figure 4 - Round nests of endocrine cells identical to normal pancreatic islets are scattered in the interstitium of the muscularis propria.

Definition and Names:
Ectopic pancreas is formally defined as pancreatic tissue that is not normally situated, has no contact with the normal pancreas, and has its own duct system (if it has ducts) and its own vascular supply. Practically speaking, it is the presence of any of the various elements of pancreatic parenchyma at a site not contiguous with the pancreas. This terminology is not generally used for examples of pancreatic acinar tissue confined to the mucosa of any part of the gastrointestinal tract (pancreatic acinar metaplasia, see below).

Pancreatic ectopias may contain any mixture of pancreatic tissues: usually ducts and mucin-producing glands, but also acini and islets. Occasionally there are only ducts or only islets. When ducts predominate, they are often surrounded by thick bundles of smooth muscle.

The common finding of predominantly ducts and muscle has led to there being a number of synonyms. The list of names includes:

  • ectopic pancreas
  • heterotopic pancreas
  • adenomyomatous hamartoma
  • myoglandular hamartoma
  • myoepithelial hamartoma
  • adenomyoma

Pathogenesis:
The pathogenesis is not known. The "misplacement theory" suggests that during embryologic rotation of the foregut, and/or during fusion of the dorsal and ventral buds, fragments of the pancreas become separated and develop into mature pancreatic tissue. This would explain the sites proximate to the pancreas, but not sites farther away, such as colon. Another theory is that pancreatic ectopia develops as a result of pancreatic metaplasia of endodermal tissue that is misplaced in the submucosa or another location during embryogenesis.

Gross and Histologic Features:
The most common locations for ectopic pancreas are upper small intestine—duodenum and upper jejunum; followed by the stomach—prepyloric region, greater curvature or posterior wall. They manifest as round or lobulated firm intramural nodules that are most often in the submucosa, but may involve the muscular wall or be subserosal. Most cases are less than 3 cm. The endoscopic appearance is of an intramural nodule that may have an umbilication on the mucosal surface, the site of a draining duct.

Ectopic pancreas may include any of the tissues of the pancreas. Ducts and collections of mucous glands associated with smooth muscle are common. Acini and variable numbers of islets may also be found.

In addition to these more common sites, ectopic pancreas has been reported in the ileum, Meckel's diverticulum, colon, spleen, liver, gallbladder and biliary tract, mesentery, esophagus, lung, ampulla of Vater, mediastinum, and lymph nodes.

Clinical Presentations:
Pancreatic ectopia is most often an incidental finding at laparotomy, or during imaging or endoscopic studies. It is clear that most examples are of no clinical import, since careful autopsies will disclose ectopic pancreas in anywhere from 2 to 25% of cases. When they are found as a result of symptoms, these symptoms include abdominal pain, gastrointestinal bleeding due to mucosal ulceration, obstruction, or intussusception.

Ectopic pancreatic tissue may be affected by any ailment that affects the normal pancreas, including pancreatitis, abscess, and ductal or endocrine neoplasms.

"Cystic dystrophy" occurs in some cases of ectopic pancreas. This consists of cysts surrounded by inflammation and fibrosis, intermingled with pancreatic ducts and lobules in the gut wall. It may present with mass-related symptoms: obstruction or stenosis of intestine or biliary tract.

Weird presentations seem to be the cause of numerous case reports in the pathology, surgery and radiology literature. They are too numerous to mention, but here are some of them:

  • Cystic change, resulting in radiologic appearance interpreted as gastric duplication cyst
  • Gastric serosal nodule composed entirely of islets interpreted as carcinoid tumor on frozen section
  • ectopic pancreas in a neonate associated with nesidioblastosis
  • in cystic duct causing acalculous cholecystitis
  • associated with (causing?) intra- and extrahepatic choledochal cysts
  • massive gastrointestinal bleeding from jejunal ectopic pancreas
  • dysphagia due to esophageal ectopic pancreas
  • Tumors: mostly ductal, some acinar or endocrine
    • Jejunal pancreatic ductal carcinoma
    • mucinous cystadenocarcinoma arising in heterotopic pancreas in the spleen
    • Anaplastic carcinoma arising in ectopic pancreas located in the distal esophagus.
    • Ductal adenocarcinoma arising in a heterotopic pancreas situated in a hiatal hernia.
    • Solid and papillary neoplasm arising from an ectopic pancreas in the mesocolon
    • Insulin-producing islet cell tumor in an ectopic pancreas of a red fox (Vulpes vulpes).
  • False-positive cytology in diagnostic laparoscopy due to ectopic pancreas.
  • Biliary cirrhosis secondary to obstruction of the common bile duct by ectopic pancreas in a cow
  • Ectopic pancreas complicated by pancreatitis and pseudocyst formation mimicking jejunal diverticulitis
  • Induction of gastroduodenal prolapse by antral heterotopic pancreas.
  • Ectopic pancreas cyst in the mesocolon
  • Ectopic pancreas presenting as an umbilical mass.
  • Ectopic pancreas in the fallopian tube
  • Etc., etc.

Pancreatic Acinar Metaplasia:
Pancreatic acinar metaplasia (PAM) is a collection of pancreatic acinar cells, often mixed with mucous glandular cells, that is found in the mucosa of the gastrointestinal tract. It does not include ducts, muscle or islets. It is considered an entity distinct from ectopic pancreas.

PAM is common in the gastric cardia found in 14% and 61% of esophagogastrectomy specimens, and 24% of biopsies in three studies. Its presence was not found to be associated with histologic evidence of gastroesophageal reflux or H. pylori. Mucosa with PAM was inflamed.

PAM has also been described in Barrett's mucosa. As a matter of fact, at one point there was speculation that it could be a marker for Barrett's mucosa, but this has not turned out to be the case.

PAM is found in the gastric antrum and body as well, but less often than the cardia. In pediatric patients, in whom antral biopsies are routine, but cardia biopsies are uncommon, 3.3% of patients have upper endoscopy with biopsy had PAM in the antrum. These patients were biopsied for a variety of indications. There is one case report of PAM in a gastric inlet patch.

Pancreatic acinar metaplasia does not seem to have any particular clinical significance, at least none that has been identified to date. Its nature, whether congenital or metaplastic, is not known for sure, despite the name.

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