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
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
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.
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
- Cystic change, resulting in radiologic appearance interpreted as gastric
- Gastric serosal nodule composed entirely of islets interpreted as carcinoid
tumor on frozen section
- ectopic pancreas in a neonate associated with
- in cystic duct causing acalculous cholecystitis
- associated with (causing?) intra- and extrahepatic choledochal cysts
gastrointestinal bleeding from jejunal ectopic pancreas
- dysphagia due to esophageal ectopic
- Tumors: mostly ductal, some acinar or endocrine
pancreatic ductal carcinoma
- mucinous cystadenocarcinoma arising in heterotopic pancreas in the
- Anaplastic carcinoma arising in ectopic pancreas located in the distal esophagus.
- Ductal adenocarcinoma arising in a heterotopic pancreas situated in a hiatal hernia.
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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