[Heterotopic tissue in the gastrointestinal tract]

Heterotopia of the gastrointestinal tract is a common finding. This is due to the complex embryogenesis and the relative ease to detect heterotopic tissue during endoscopy. The reason for biopsy is mostly to rule out neoplasms or to define specific causes of inflammation. Heterotopic tissue can occur in any location of the gastrointestinal tract. The most frequent are gastric heterotopia, pancreatic heterotopia, and heterotopia of Brunner's gland. On rare occasions, heterotopic tissue of salivary gland type as well as heterotopias of apocrine glands, thyroid, and prostatic tissue have been described. The most frequently involved organs are the small intestine, in particular the duodenum, the esophagus, and the stomach. Heterotopia of the large bowel occurs exclusively in the rectum. Most heterotopias do not cause symptoms and are easily diagnosed by biopsy and histology. However, depending on location, size, and the kind of underlying heterotopic tissue, they may cause significant complications, such as inflammation, ulceration and perforation, obstruction, intussusception, and severe life-threatening bleeding. Another rare but significant complication is neoplasia. Gastric heterotopias may give rise to pyloric gland adenomas within the bowel or rarely adenocarcinomas of the esophagus. Pancreatic heterotopia can be complicated by ductal type pancreatic adenocarcinomas, by acinus cell carcinomas, by intraductal papillary mucinous neoplasias, and also by endocrine tumors. The present paper summarizes our current knowledge about heterotopias in a topographic clinico-pathological manner.