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Pancreatic tissue is present outside its normal location.

Aberrant (ectopic) pancreas, which is incidentally found in 2% of all routine postmortem examinations.   

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This anomaly is most commonly localized in the wall of the stomach, duodenum and jejunum, 

More rarely, it has been found in Meckel's diverticulum of the ileum, the common bile duct, gall bladder, liver, spleen and various other foci in the abdominal cavity.

In the wall of the gastrointestinal tract, pancreatic nodules localize immediately below the mucosa, in the muscularis beneath the serosa, or in small diverticula.

The tissue contains all the components of normal pancreas, namely, acini, ducts, and islets.

The most plausible theories of the origin of aberrant pancreas are:

(1) Incomplete atrophy of the left ventral anlage;

(2) Regression to a more primitive pattern of differentiation reminiscent of that seen in lower vertebrates, especially certain fish in which exocrine and endocrine pancreatic tissue are diffusely distributed in liver, intestinal wall, and peritoneum;

(3) Inappropriate expression of the pleuripotent developmental capacity of the embryonic gut;

(4) Buds of embryonic pancreatic tissue that have penetrated the intestinal wall and have become isolated from the main mass and thus misplaced by rapid longitudinal growth of the intestine.

Of these theories, the last two (3) and (4) seem more probable.

Ectopic pancreas is a rare entity but the second most prevalent pancreatic anomaly. Heterotopic pancreas is defined as the presence of pancreatic tissue without any anatomic or vascular continuity with the main body of the pancreas. Its aetiology is not clearly established. In 1916, Poppi published for the first time evidence of heterotopic pancreas in the gallbladder. A review of the literature up to the present showed only 28 more cases worldwide of ectopic pancreas in the gallbladder. Aberrant pancreas is incidentally discovered in 2% of autopsies and has been estimated to occur once in every 500 upper abdominal explorations. Ninety per cent of ectopic pancreas is found in the stomach, duodenum, and jejunum. Mostly it is asymptomatic and benign. For this reason, therapy is indicated only in patients with symptoms such as pyloric obstruction, bleeding, and malignant transformation. Surgical resection or endoscopic mucosal resection as a newer method are recommended.

Heterotopic pancreas mimicking cholangiocarcinoma. Case report and literature review.JOP. 2007 Jan 9;8(1):28-34.

CONTEXT: Majority of the patients developing obstructive jaundice have an underlying malignancy. Identification of a benign pathology like heterotopic pancreas as an aetiology is uncommon and usually occurs only subsequent to a major operation. CASE REPORT: We report a case of heterotopic pancreas adjacent to the ampulla of Vater mimicking distal cholangiocarcinoma. A 47-year-old patient presented with abdominal pain and obstructive jaundice. ERCP demonstrated a distal common bile duct stricture suspicious of cholangiocarcinoma. He underwent a pylorus-preserving pancreaticoduodenectomy. Histology showed a nodule of heterotopic pancreatic tissue adjacent to the ampulla. CONCLUSION: We have reviewed the literature on heterotopic pancreas of the periampullary region presenting with biliary obstruction. This is a rare entity and remains difficult to diagnose, despite advances in radiological and endoscopic imaging techniques. For symptomatic patients with an established diagnosis of periampullary heterotopic pancreas, local excision may be sufficient. However, in the absence of unequivocal imaging or histological confirmation of benign pathology, and when there is a suspicion of underlying malignancy, pancreaticoduodenectomy may be the only treatment option, as in this case.

A rare case of ectopic pancreas in the ampulla of Vater presented with obstructive jaundice.Ann Ital Chir. 2006 Nov-Dec;77(6):517-9.

A rare case of ectopic pancreas in the ampulla of Vater presented with obstructive jaundice. Ectopic pancreas is a common congenital disorder which is referred to as pancreatic rest. The incidence in autopsy series varies from 1 to 2% (range 0.55 to 13%). Most common site of ectopic pancreatic tissue is the stomach, although it can be found anywhere in the foregut and the proximal midgut. Ectopic pancreatic tissue in the ampulla of Vater is a very rare condition. Searching in the literature, using the terms "ectopic pancreas" and "Ampulla of Vater", we found only 10 records. The authors report on a rare case of a 69 years old female with ectopic pancreas in the ampulla of Vater, presented with painless obstructive jaundice, and the diagnostic and therapeutic strategy that followed.

Cancer of an ectopic pancreas in the duodenal wall.Gastroenterol Clin Biol. 2005 Feb;29(2):201-3.

Ectopic pancreas is defined as pancreatic tissue outside the normal location of the pancreas. It can be affected by the same complications as the orthotopic pancreas, such as adenocarcinoma. This extremely rare complication (only 14 published cases) may have a better prognosis that adenocarcinoma of an orthotopic pancreas. Endoscopic ultrasonography may be useful in the diagnosis of this disease. We report a case of malignancy of the duodenal wall originating in aberrant pancreatic tissue, and review the literature.

A case of proximal jejunal ectopic pancreas causing sporadic vomiting.
Turk J Pediatr. 2003 Apr-Jun;45(2):161-4.

Aberrant rests of pancreatic tissue can be found throughout the gastrointestinal system and are known as pancreatic heterotopia or ectopic pancreas (EP). Authors report a 12-year-old girl with jejunal EP with a long-lasting history of sporadic bilious vomiting. Upper gastrointestinal (GI) study showed delayed passage beyond duodeno-jejunal junction. During laparotomy a 2x2 cm mass was encountered on the mesenteric border of the jejunum, 3 cm distal to the ligament of Treitz. Histopathologic examination revealed pancreatic tissue. The mass was excised and end-to-end anastomosis was performed. Postoperative course of the patient was uneventful and she is doing well after 10 months. Intestinal obstruction due to EP has been reported to occur only if it causes intussusception. Intestinal obstruction without intussusception due to jejunal EP has not been reported. In our case, the EP tissue was located just beneath the mucosa and involved the muscular layer. The foreign body effect of the EP tissue involving the muscular layer may cause dysmotility and/or local spasm, which we think were responsible for the long-lasting sporadic bilious vomiting in our patient.

Gastric aberrant pancreas: EUS analysis in comparison with the histology.Gastrointest Endosc. 1999 Apr;49(4 Pt 1):493-7.

BACKGROUND: Histologic diagnosis of aberrant pancreas is usually difficult when tissue samples are obtained with a standard biopsy forceps. The aim of this study was to describe the endosonographic (EUS) features of gastric aberrant pancreas. METHODS: EUS was performed in 10 patients with aberrant pancreas before resection. EUS features of the lesions were analyzed and compared with resected specimens retrospectively. RESULTS: EUS in 5 lesions (50%) demonstrated the ectopic pancreatic tissue as located in the third and fourth sonographic layers (submucosa and muscularis propria) and in the third layer (submucosa) in the other 5 lesions. The margin appeared for the most part indistinct (80%) because of the lobular structure of the acinous tissue. The internal echo pattern in all cases was heterogeneous, mainly a hypoechoic image (acinous tissue) accompanied by scattered small hyperechoic areas (adipose tissue). An anechoic area (duct dilatation) (80%) and fourth-layer thickening (muscular hypertrophy) (80%) were commonly visualized. CONCLUSION: Gastric aberrant pancreas has characteristic EUS features that correlate with specific histologic components and is variable with regard to sonographic layer of origin.

Ectopic pancreas with gastric localization: a clinical case and review of the literature.G Chir. 1994 Apr;15(4):162-6.

Heterotopic pancreatic tissue localized in the upper gastrointestinal (UGI) tract rarely presents with symptoms unless it is complicated by bleeding or mucosal ulceration. The case of a 26 year old man who presented with a one year history of epigastric pain, dyspepsia and several episodes of vomiting, without signs of bleeding or ulceration is reported. Work-up, which included upper gastrointestinal endoscopy, abdominal ultrasound and UGI series, revealed an intramural mass on the lesser curvature of the stomach, with normal overlying mucosa. The patient underwent surgical excision of the lesion and histologic examination showed normal pancreatic tissue. Postoperatively the patient did well with marked clinical improvement. In reviewing the literature on aberrant pancreatic lesions of the stomach the Authors discuss the varying clinical presentation and differential diagnosis as well as treatment options: when the lesions present with disabling symptoms, surgical excision should always be performed.

Pancreatic heterotopia: a reappraisal and clinicopathologic analysis of 32 cases.South Med J. 1988 Oct;81(10):1264-75.

A total of 32 histologically documented cases of heterotopic pancreas was found in a review of the records of the department of pathology at the Chang Gung Memorial Hospital between 1977 and 1987. This review was done to ascertain the clinical significance of this uncommon entity. In 14 patients (44%), the aberrant pancreatic tissue was symptomatic; in the other 18 (56%), it was found incidentally. In the symptomatic group, the heterotopic pancreatic tissue was found in a duplication cyst of the ileum in one patient, in the common bile duct in one, in a Meckel's diverticulum in four, in the stomach in three, in a congenital duodenal diaphragm in one, in the duodenum in three, and in the ileum in one. The majority of heterotopic pancreatic tissue in the asymptomatic group was encountered in the jejunum (15 patients). Symptoms were related to complications, including obstruction of the common bile duct, mucosal ulcer with hemorrhage, intussusception, and intestinal obstruction, but not to pathologic conditions of the pancreas itself, such as pancreatitis or pancreatic cyst or neoplasm. In all of the clinically significant cases, the clinical symptoms disappeared completely after surgical removal of the aberrant tissue. In 28 cases (87%), diagnosis was made by frozen section during operation. Preoperative diagnosis of aberrant pancreas was not made in any of the cases. Histologically, all cases showed pancreatic excretory ducts; in 31 cases (97%), exocrine glands were present, and in 27 cases (84%), islets of Langerhans were discernible. There was no relationship between symptoms and the presence of islets, acini, or ducts. Mallory's phosphotungstic acid-hematoxylin stain was used to demonstrate zymogen granules in the acinar cells, and insulin, glucagon, and somatostatin were demonstrated with the horseradish peroxidase-antihorseradish peroxidase immunocytochemical staining technique; islets of Langerhans were also identified. Technetium Tc 99m scintigraphy was used to detect the bleeding source in a Meckel's diverticulum and an enteric duplication associated with ectopic gastric mucosa.