Congenital alimentary tract malformations are rare developmental mass lesions that can occur anywhere in the entirety of the gastrointestinal (GI) tract. These lesions have been assigned several different names, including enterocystomas, enterogenous cysts, supernumerary accessory organs, ileum duplex, giant diverticula, giant thoracic cysts, and unusual Meckel diverticulum.
As suggested by Gross, current nomenclature relies on the anatomic location of the duplication in relation to the normal intestinal tract and does not rely on the histologic features of the mucosal lining.  Further characterization defines these abnormalities as either cystic or tubular. Although intestinal duplications are considered to be benign lesions, they may result in significant morbidity and mortality if left untreated.
This article reviews the incidence, embryology, anatomy, common clinical presentations, principles of diagnosis, and surgical interventions of the spectrum of alimentary tract duplications.
History of the Procedure
The term intestinal duplication was first used by Fitz in 1844 in a paper suggesting that alimentary tract duplications arose from persistent omphalomesenteric remnants.  but was not widely adopted until it was popularized by Ladd in the 1930s,  with further classifications by Gross in the 1950s.  Calder is said to have first reported lesions similar to them in 1733.  Ladd was the first to use the term duplication of alimentary tract, applying it to congenital lesions having the following three characteristics:
Epithelial lining of GI mucosa
Presence of well-developed smooth muscle in the wall
Association with the GI tract
Because of the relative scarcity of such anomalies, the current literature mainly consists of small populations and case reports rather than any large multi-institutional series.
Intestinal duplications are intimately attached to an adjacent segment of normal intestine (ie, share a common wall). Such anomalies possess at least one exterior coat of smooth muscle and are lined with various types of GI mucosa.
Approximately two thirds of all intestinal duplications are discovered within the first 2 years of life, with one third identified in the newborn period. Although the exact incidence is unknown, Potter in 1961 reported two cases in more than 9000 fetal and neonatal autopsies.  They may be slightly more common in males.  About 80% of intestinal duplications are found in the abdomen, 20% in the thoracic cavity. Because multiple duplications may be present in as many as 20% of patients, other duplications should be sought if one duplication is diagnosed.
Because duplication of the alimentary tract takes many different forms, application of a single embryologic theory is not likely to be considered valid. This has led to the proposal of several different theories in an attempt to explain the embryologic events that culminate in intestinal duplication. The etiology therefore is generally based on the supposed origin or nature of the duplication.
The supposed origin of an alimentary tract duplication may be from the foregut, the midgut, or the hindgut.
The duplication may be extremely short or may include a large amount of the length of the normal intestine. It may thus be described as either cystic or tubular in nature. In contrast to the cystic variety, the tubular variety may communicate with the normal intestine at one or several points along the common wall.
There are four major theories regarding the origin of duplication cysts:
Partial twinning theory
Split notochord theory
Canalization defects theory
Environmental factors theory
The partial twinning theory states that organs can be double as a result of abnormal twinning. Multiple organs can be formed in such cases and major skeletal abnormalities might also be noted. Some cases have been reported for complete doubling of a set of organs. Such cases can be explained by late abortion of this twinning process.
The split notochord theory, first postulated by Bentley, states that during the third to forth week of gestation, when the notochord starts separating from the endodermal cells, gaps may appear in the notochord through which endodermal cells can herniate and form diverticula. This theory may explain long duplication cysts, as well as intrathoracic or foregut duplications. It proposes an explanation for the 15% of enteric duplications with associated vertebral defects.
The canalization defects theory is based on the process by which all GI organs begin as solid organs in the embryologic state and gradually vacuolate to form the lumen. During this process, multiple diverticula form in the fetal stage, which regress with development. Some postulate that this may be the most common explanation, in that most of these fetal diverticula are found in the ileum, the most common site of duplication cysts. This is said to happen at 5-8 weeks' gestation.
The environmental factors theory postulates that stress, hypoxia, and trauma may induce duplications. Vascular accidents and compression from other organs may explain a few of these findings.
Most duplications are incidentally diagnosed. In some instances, they are diagnosed on prenatal ultrasonography. Those that are missed on prenatal ultrasonography are usually diagnosed by the second or third year of life.
Most patients present with a combination of pain and obstructive symptoms. These symptoms may be the direct effects of distention of the duplication or may be caused by compression of adjacent organs (including their associated blood supplies). In addition, abrupt hemorrhage with hemodynamic instability can be encountered in the case of a cyst lined with gastric mucosa  that ulcerates and eventually erodes into adjacent organs or vessels. The presentation usually depends on the location of the duplication cyst.
Duplications in the chest usually present as pulmonary symptoms or dysphagia. Pain may be noted. The lesion is often picked up as a cystic mass on a chest x-ray.
Pain and vomiting are the usual symptoms associated with duplications in the abdomen.
Duplications arising from the foregut, besides causing pain and vomiting, can give rise to bleeding and perforation from ulceration. They may also present as gastric outlet obstruction and therefore must be differentiated from hypertorophic pyloric stenosis and other causes of gastric outlet obstruction.
Duplications arising from the midgut can cause pain in the right lower quadrant and may be confused with appendicitis. In some cases, the duplication cyst may cause intussusception.
Duplications arising from the hindgut can present as a secondary opening in the perineum; in females, they can also form a rectovaginal fistula. Symptoms in these cases can range from obstruction to incontinence. Mass effect from these cysts, which tend to be giant, can also cause obstruction of the ureters.
Indications for surgical intervention with regard to duplications of the alimentary tract often arise in an acute setting. Specifically, patients with previously undetected duplications may present in the setting of bowel obstruction or severe GI hemorrhage (ie, ulcerating gastric mucosa within a duplication cyst). If incidentally encountered, duplications should be surgically addressed to avoid future complications.
A review of the literature regarding alimentary tract duplications in more than 500 patients reveals a widely varied anatomic distribution (see the image below). Approximately 75% of duplications have been reported to be located within the abdominal cavity, whereas the remaining are intrathoracic (20%) or thoracoabdominal (5%). Jejunal and ileal lesions are the most commonly encountered (53%), followed by mediastinal (18%), colonic (13%), gastric (7%), duodenal (6%), rectal (4%), thoracoabdominal (2%), and cervical (1%) lesions.
Some 75-80% of duplications are considered cystic, with no communication to adjacent intestine, whereas the remaining duplications are true cylindrical structures that may or may not have one or more direct communications across the common septum.
All intestinal duplications contain at least one layer of smooth muscle and some type of intestinal mucosal layer within the lumen. They are often intimately attached to an adjacent segment of the normal GI tract; sacrificing a segment of normal intestinal tract is sometimes necessary during the resection of a duplication cyst.
The mucosal lining within alimentary tract duplications does not necessarily correspond with the adjacent normal intestine and may display components of several different types of GI tract mucosa. Noncommunicating duplications typically contain clear alkaline fluid, except in cases where gastric mucosa is present (25%) and acidic fluid is observed. In addition, nonactivated pancreatic enzymes may also be observed in cases of ectopic pancreatic tissue within the duplication lesion. 
Cervical and thoracic duplications
Esophageal duplications are relatively uncommon, and patients tend to present at a later age than those who have duplications in other areas of the alimentary tract.
Although duplications of the esophagus are reported throughout its length, most are located in its distal half. These lesions are cystic and located in the posterior mediastinum (more commonly on the right side than the left side), with a high association of vertebral abnormalities (eg, spina bifida, hemivertebrae, myelomeningocele) compared with nonthoracic duplications. Additionally, posterolateral diaphragmatic herniation and esophageal atresia have been reported in association with esophageal duplications.
Esophageal duplications account for approximately 20% of all duplications. Gastric mucosa has been reported to be present in approximately 30-50% of esophageal duplications; it frequently gives rise to bleeding secondary to mucosal ulceration and erosion into adjacent structures. Excision of the cyst is advised for these duplication cysts.
Thoracic and thoracoabdominal duplications
These lesions account for 20% of all duplication cysts. Thoracoabdominal lesions, like thoracic lesions, are more often located on the lower end of the posterior mediastinum, most commonly on the right side. These are also called neuroenteric cysts. They tend to have associated spinal and vertebral anomalies as well. Generally considered rare, they are believed to represent long diverticula that originate in the intestine and extend into the thoracic cavity.
Prenatal ultrasonography has been able to diagnose these.
Various in-utero therapies have been used, with variable results. Before surgery, endoscopic ultrasonography and barium swallow help distinguish them from the esophagus. Electrocardiography (ECG) may help differentiate them from pericardium. Computed tomography (CT) and magnetic resonance imaging (MRI) are also done to delineate the anatomy and detect any synchronous lesions.
Surgical procedures for treating these lesions are complicated. Thoracoscopic surgery is the main approach. Intra-abdominal extensions may necessitate laparotomy at the same time or in a staged manner. If the lesions is associated with spinal and vertebral anomalies, a neurosurgeon should usually be consulted for assistance.
Duplications involving the stomach are the least common of the abdominal duplications (~5%). They are more prevalent in males than in females, and patients present at a mean age of 3 years (one third are diagnosed during the neonatal period). Gastric duplications are typically noncommunicating cystic structures located along the greater curvature or posterior aspect of the stomach, but they have been reported at the level of the pylorus and may be mistaken for hypertrophic pyloric stenosis. 
Duodenal and pancreatic duplications
Duodenal duplications vary in size and are most often located posteromedially, sharing a common wall with the true duodenum and often partially embedded in the head of the pancreas. Obstruction is the most common clinical presentation; however, pancreatitis [10, 11] and peptic ulceration of gastric mucosa within the duplication have also been reported. Pancreatic duplication is the rarest individual type of duplication cyst.
Surgical procedures in these areas are technically challenging, necessitating further diagnostic workup (eg, pancreas protocol CT and magnetic resonance cholangiopancreatography [MRCP]). Endoscopic retrograde cholangiopancreatography (ERCP) may be necessary to aid in managing biliary and pancreatic duct obstruction. ERCP is also done to facilitate surgical planning. When the anatomy is difficult and complete resection might involve major morbidity, incomplete excision with internal drainage and marsupialization of the cyst may be an operative option.
Jejunal and ileal duplications
Duplications of the ileum represent the most common form of alimentary tract duplication and typically appear as noncommunicating spherical cysts of varying sizes. When they take the form of long tubular segments, they tend to distend and cause extrinsic compression and thus obstructive symptoms. Because of their common location at the mesenteric border, they are easily mistaken for mesenteric or omental cysts, only to be clarified by identification of a mucosal rather than endothelial lining. They can present as intussusceptions.
Li from Beijing characterized these cysts into type 1 and type 2 lesions. In type 1, also called the parallel type, there are two blood vessels, one perfusing the normal vessel and the other the duplication cyst. In type 2, also called the intramesenteric type, the vessel traverses the duplication on its way to perfusing the native intestine.
In duplications of the hindgut, the long or short segments of the distal ileum, cecum, appendix, and entire colon are duplicated and drain through one or several perineal openings.  These account for 17-20% of all duplication cysts. The malformation may be accompanied by imperforate anus, involving both the normal anus and the pathologic opening; it has been associated with bladder abnormalities, duplication of external genitalia, and extrapulmonary sequestration  with esophageal communication.
Colonic or rectal duplications may distend secondary to inadequate distal drainage, resulting in obstruction and even perforation. Cystic and tubular duplications of the colon are rare entities. Cystic duplications have been reported to cause obstruction of the large bowel as a result of direct compression, volvulus, and intussusception,  whereas tubular duplications of the rectum have been described as having direct communication with the perineum. When draining into the vagina in females, they can cause rectovaginal fistula.
These lower duplications are difficult to treat. Extensive workup is needed to predict postoperative function. Patients can have debilitating problems with incontinence and wounds.
Hindgut duplications may be divided into three classes as follows:
Small intra-mesenteric duplications - These are usually cystic or small tubular lesions; similar to midgut duplications, they are usually treated with excision; resection of the native bowel is frequently required as well
Midline masses - These develop between the rectum and the sacrum; resection involves major reconstructions
Long tubular side-to-side duplications - Resection of these lesions is extremely complicated and carries a high morbidity; partial resection, marsupialization, and fenestrations are some options that may be employed to reduce the morbidity associated with complete resection
No specific contraindications to the surgical management of alimentary tract duplication are recognized. The contraindications are relative, mostly associated with complicated excision necessitating extensive reconstruction. Anesthetic complications should also be considered during nonemergency surgical procedures.
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