Duplications of the gastrointestinal tract occur from the tongue to the anus. Classification was simplified by Ladd in 1937, when he pointed out that lesions throughout the gastrointestinal tract, previously termed enteric cysts, enterogenous cysts, diverticula, giant diverticula, ileum duplex, jejunum duplex, and unusual Meckel's diverticula, shared common characteristics and treatment.

Duplications have three common features regardless of their location. They are hollow structures, lined with gastrointestinal tract epithelium, which have a smooth muscular wall, often shared with the contiguous intestinal tract. The epithelial lining of the duplication may be different (heterotopic) from that of the adjacent bowel. Symptoms vary depending upon the location of the duplication, but are produced by the mass effect of the cyst, which causes obstruction of the intestinal tract or airway, or by haemorrhage or perforation caused by acid secretions from heterotopic gastric mucosa within the cyst. Rarely, volvulus of an affected segment of bowel may occur. While duplications may present themselves at any age, they generally are identified in infancy or childhood.

In considering the aetiology of duplications, Lewis and Thyng identified intestinal tract diverticula budding into the subepithelial connective tissues during development. These diverticula may become isolated from the intestinal lumen to form cysts; however, the diverticula occur around the entire circumference of the bowel and are not limited to the mesenteric border, where duplications are found. Incomplete resolution of the solid phase of the intestinal tract, when the lumen of the intestine is entirely filled with epithelial cells during early development, may produce duplications. Such cysts, however, would not be limited to the mesenteric border of the bowel nor surrounded by a separate smooth muscle wall. In human embryos the solid stage of enteric development has not been identified distal to the duodenum. A more acceptable explanation for some duplications involves the persistence of the neuroenteric canal, the embryonic communication between neural ectoderm and the gastrointestinal endoderm. Such an event, resulting in the canal extending through the mesodermal layer which forms the spine (the notochord), will result in a dorsal enteric fistula or communication between the intestine and the dorsal skin surface, passing through a bifid spinal cord. Lesser degrees of this process with only partial resolution of the canal may result in cystic duplications; in some cases duplications are associated with abnormalities of the spine.

Extensive colonic duplications appear to be a result of partial ‘caudal twinning’ because they are often associated with duplication of the urinary tract and external genitalia. Their aetiology may be distinct from that of other forms of duplication. Duplications are occasionally seen in association with atresia of the intestine: this was noted in 11 per cent of 68 cases reported by Gross and associates. Multiple atresias are seen in 15 per cent of patients.

The frequency of duplications throughout the intestinal tract is shown in Fig. 1 2139. Duplications occur most frequently in the ileum; the second most common site is the oesophagus. Although Ladd stated that none of the patients in his initial report was diagnosed before surgery, most are now identified by imaging before exploration. Thoracic lesions are often discovered incidentally on radiographs of the chest; a barium swallow or CT scan may be required to define the lesion fully. Abdominal duplications are reliably defined on ultrasound examination, because of their cystic nature. The radionuclide [&sup9;&sup9;Tc&supm;]pertechnetate macroaggregated albumin scan can demonstrate the presence of heterotopic gastric mucosa within the duplication.

Resection of duplications is recommended once they are identified, since large cystic lesions of the colon and ileum may perforate following progressive distension by mucosal secretions or may cause intestinal obstruction. Neoplasia has been described at almost every site of duplication, but usually occurs in patients 26 to 65 years old. Both squamous carcinoma and adenocarcinoma have been reported.

Oesophageal duplications may produce dysphagia or respiratory distress, particularly when present in the cervical oesophagus or between the trachea and oesophagus in the upper mediastinum. Many, however, are asymptomatic and are identified on chest radiographs obtained for other reasons (Fig. 2) 2140,2141.

Resection of oesophageal duplications is performed through a thoracotomy. Recognition of the shared wall between the cystic duplication and the oesophagus is critical to avoid injury to the oesophagus. The muscular layer overlying the cyst is opened and the muscosal portion of the cyst is dissected from the shared oesophageal wall. The epithelial lining may be squamous, ciliated respiratory, or, less frequently, ectopic intestinal or gastric mucosa. Communication with the oesophageal lumen is rare. Bronchogenic cysts occurring within the mediastinum are thought to result from diverticula of the bronchial tree. They may also have a squamous epithelial lining similar to the oesophagus since they share a common embryological anlagen. They are distinguished from oesophageal duplication cysts only by their lack of proximity to the oesophagus.

Large cystic duplications within the thorax may communicate distally with the duodenum or intestine. Patients harbouring these duplications may present with respiratory symptoms secondary to the large size of the duplication, sepsis from intestinal colonization, or haemorrhage from peptic erosion arising from heterotopic gastric mucosa. Large thoracoabdominal duplications extending into the thorax through the diaphragm are often adherent to the spine and are frequently associated with spinal anomalies. Complete resection is required and may be performed through a thoracoabdominal incision or through separate thoracic and abdominal incisions.

Gastric duplications are generally identified within the first year of life. Presenting symptoms and signs include a palpable abdominal mass, vomiting, weight loss, abdominal pain, anaemia, melaena, haematemesis, or fever. Of the 83 cases reviewed by Pruksapong most occurred along the greater curvature (54), with fewer along the lesser curve (7), anterior wall (5), posterior wall (9), or in the region of the pylorus (1). In seven cases the location was not well described. Communication with the gastric lumen is unusual unless it occurs secondary to peptic erosion.

Gastric duplications require surgical excision. A limited partial gastrectomy of the shared wall is often performed for lesions of the greater curve, but in lesions of the lesser curve a submucosal resection can be performed.

Pyloric duplications are very rare. Gastric outlet obstruction is often the presenting symptom and resection of the duplication may be curative.

Duodenal duplications are rare and occur primarily in the first and second portions of the duodenum, on the pancreatic margin. In 50 cases of duodenal duplication summarized by Leenders and associates, 45 were posterior to the duodenum; only four communicated with the lumen. In contrast to what are termed peripancreatic duplications, they do not communicate with the pancreatic duct. Because of their location, submucosal resection to remove gastric mucosa is often required to avoid pancreatic injury. A cystoduodenostomy may be performed for lesions without gastric mucosa, but resection is preferred and marsupialization into the peritoneal cavity is to be avoided.

Peripancreatic duplications present with symptoms of nausea, vomiting, weight loss, and abdominal pain. The majority (62 per cent) occur within the head of the pancreas, and most communicate with the pancreatic duct. Most contain gastric mucosa (90 per cent). Intermittent bathing of the pancreatic duct by acid secretions produces pancreatitis and the presenting symptoms. Identification of these lesions may be difficult, but they should be sought in every patient presenting with ‘idiopathic’ pancreatitis in childhood. Ultrasound examination shows a cystic area within or adjacent to the pancreas. Endoscopic retrograde cholangiopancreatography may demonstrate communication with the pancreatic duct, but if inflammation is present, the cyst may not fill.

At surgery the mucosal lining of the cyst must be removed if the cyst itself cannot be resected completely. Pancreatoduodenectomy has been performed in some patients in whom lesser options were not suitable to achieve complete removal of the cyst or its lining.

Intestinal duplications are found within the leaves of the mesentery, with the blood supply to the intestine draped over their surface. Smaller lesions may be missed if the mesentery is not closely inspected. They occur as either a long tubular duplication extending along a significant length of small intestine, or as small spherical cysts. Signs and symptoms include obstruction caused by the spherical lesions and, occasionally, intussusception. Less frequently, intestinal bleeding, perforation, or abdominal pain occur when ectopic gastric mucosa is present.

Limited spherical duplications, which are generally lined with intestinal mucosa, are treated by resection of the cyst and its overlying intestinal segment, with primary anastomosis. Long tubular lesions present greater challenge. Removal of these lesions is important since they often contain heterotopic gastric mucosa and communicate distally with the intestinal lumen. Acid secretions produce ulceration within the duplication or in the ileum distal to its communication with the duplication. Wrenn described a technique for submucosal resection of the duplication through a series of transverse incisions in the seromuscular wall of the cyst placed between mesenteric vessels (Fig. 3) 2142. This technique allows the entire mucosal lining of the duplication to be excised without resection of any intestine. Resection of the entire cyst between the leaves of the mesentery can be performed only if the muscular wall is not shared with the intestine, an unusual occurrence. An innovative approach to this problem is creation of an anastomosis between the stomach and the distal end of a complete intestinal duplication containing gastric mucosa. This diversion of the acid secretions of the duplication into the stomach prevents ileal or colonic peptic ulceration, and long-term follow-up has shown no evidence of blind loop syndrome or malabsorption.

Colonic duplications also occur in two forms. Limited spherical duplications occur most frequently at the caecum and are managed by partial colectomy. Long tubular duplications may extend from the ileum to the anus, and are often associated with other anomalies (80 per cent), including spina bifida and duplications of the bladder, urethra, or external genitalia. The proximal end of a tubular colonic duplication invariably communicates with the bowel lumen; half of all tubular duplications have a fistula at the distal end, connecting to the urinary tract, vagina, vulva, or perineum. Duplicated anus is rare. Tubular duplications without a distal fistula become massively distended in the distal portion of the duplication.

Tubular duplications of the colon occur on the mesenteric or antimesenteric surface of the colon suggesting a different embryological origin from that of the more proximal duplications, which invariably occur on the mesenteric surface. The mucosal lining of these lesions is generally colonic mucosa. A radionuclide scan will exclude the presence of ectopic gastric mucosa in the duplication which would require resection. Surgical management of total colonic duplications lined by colonic mucosa involves division and proximal dissection of the distal fistula to the urinary tract or perineum. A fenestration is then placed between the abnormally ending duplication and the colon at a site where they share a common wall (Fig. 5) 2145. The duplication segment should be excised beyond the fenestration to avoid distension of a blind ending segment.

Rectal duplications are spherical and occur between the rectum and the sacrum. The differential diagnosis of these lesions includes anterior myelomeningocele and sacrococcygeal teratoma. Rectal duplications are best managed by total excision from a transanal or perineal approach. Excision of the common wall is not recommended because stool in the diverticulum produced by the duplication is not effectively evacuated.

Mesenteric cysts are cystic lesions of the intestinal mesentery lined with endothelium. Symptoms caused by mesenteric cysts are primarily pain resulting from traction on the mesentery or partial intestinal obstruction, vomiting, and failure to thrive; obstruction arises due to recurring segmental volvulus or chronic partial obstruction. Because the cysts are soft, a mass is rarely palpable. Although radiographs reveal only a gasless area in the abdomen, ultrasound will demonstrate a large cystic lesion.

Only 700 cases had been reported by 1975. The primary aetiology of these lesions is probably abnormal development of the lymphatic system of the mesentery, resulting in stasis and progressive distension of lymphatic channels.

Mesenteric cysts are unilocular or multilocular. In contrast to the intestinal duplications they lack a muscular wall and are lined with endothelial cells rather than intestinal mucosa. Their contents are serous or chylous and rarely bloody, unless associated with recent trauma. Most mesenteric cysts are found in association with small intestine, less frequently in association with the mesocolon of the transverse, sigmoid, or right colon.

Treatment of mesenteric cysts is by surgical resection. A segmental resection of the involved loop of intestine is often required because of the intimate proximity of the cysts to the bowel wall.

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