Alimentary Tract Duplications 

Congenital alimentary tract malformations are rare developmental errors that have been assigned several different names, including enterocystomas, enterogenous cysts, supernumerary accessory organs, ileum duplex, giant diverticula, and unusual Meckel diverticulum. The term intestinal duplication was first used by Fitz^[1] but was not widely used until it was popularized by Ladd in the 1930s,^[2] with further classifications by Gross in the 1950s.^[3]

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 (which can vary).^[3] Further characterization defines these abnormalities as either spherical 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 and principals of diagnosis, and surgical interventions of the spectrum of alimentary tract duplications.

Fitz first used the term intestinal duplication in 1844 when he published a paper in which he suggested that alimentary tract duplications arose from persistent omphalomesenteric remnants.^[1] Because of the relative scarcity of such anomalies, current literature mainly consists of small populations and case reports rather than any large single or 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.

Frequency

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 reported 2 cases in 1961 in more than 9000 fetal and neonatal autopsies.^[4]

Because duplication of the alimentary tract takes many different forms, the 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 split notochord theory proposes a neural tube traction mechanism as an explanation for the 15% of enteric duplications with associated vertebral defects. Specifically, an embryologic error may result in abnormal diverticularization of the GI endoderm through the developing notochord at 4 weeks' gestation. A second theory suggests that a failure in the regression of embryonic diverticula occurs, resulting in the formation of enteric cysts. A third proposal offers the suggestion that external compression of adjacent loops of bowel may result in side-by-side duplication caused by adherence of 2 loops. Finally, errors in epithelial recanalization (believed to occur at 5-8 weeks' gestation) have been proposed as a possible explanation for the existence of small submucosal duplications.

Although many duplications are incidentally diagnosed, 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^[5] that ulcerates and eventually erodes into adjacent organs and/or vessels.

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 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. Seventy-five percent 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 in which 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 compared with 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. Gastric mucosa has been reported to be present inapproximately30%ofesophagealduplications; it frequently gives rise to bleeding secondary to mucosal ulceration and erosion into adjacent structures.

Thoracoabdominal duplications

These duplications are also considered to be rare and are believed to represent long diverticula that originate in the intestine and extend into the thoracic cavity. Thoracoabdominal lesions are more often located on the right side of the posterior mediastinum than on the left (similar to thoracic duplications).

Gastric duplications

Duplications involving the stomach are the least common of the abdominal duplications (approximately 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 curve or posterior aspect of the stomach but have been reported at the level of the pylorus and may be mistaken for hypertrophic pyloric stenosis.

Duodenal 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^{[6, 7]} and peptic ulceration of gastric mucosa within the duplication have also been reported.

Jejunal and ileal duplications

Duplications of the ileum represent the most common location of all alimentary tract duplications and typically appear as noncommunicating spherical cysts of varying sizes. Because of their common location at the mesenteric border, they may be easily mistaken for mesenteric or omental cysts, only to be clarified by identification of a mucosal rather than endothelial lining.

Tubular duplications

These may be extremely short or comprise a large amount of the length of the normal intestine. As opposed to spherical cysts, the tubular variety may communicate with the normal intestine at one or several points along the common wall.

Duplications of the colon and rectum

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,^[8] whereas tubular duplications of the rectum have been described as having direct communication with the peroneum.

Hindgut duplications

Another entity that has been described is hindgut duplication, wherein the distal ileum, cecum, appendix, and entire colon are duplicated and drain through one or several perineal openings. This 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^[9] with esophageal communication. Colonic and/or rectal duplications may distend secondary to inadequate distal drainage, resulting in obstruction and even perforation.

No specific contraindications to the surgical management of alimentary tract duplication are recognized.