Duodenal atresia represents complete obliteration of the duodenal lumen. A duodenal diaphragm (or duodenal web) is thought to represent a mild form of atresia. Duodenal stenosis (incomplete obstruction of the duodenal lumen) is discussed with duodenal atresia because the 2 disorders together represent a spectrum of similar intrauterine events.
Annular pancreas occurs when pancreatic tissue surrounds the second portion of the duodenum. If the encirclement is complete, it may be associated with complete or incomplete duodenal obstruction. Since duodenal atresia or duodenal stenosis occurs in all cases of annular pancreas, the anomalous pancreas should be considered a secondary change rather than a primary cause of duodenal obstruction.
Pathophysiology
The etiology of duodenal atresia and stenosis is unknown. Failure of recanalization of the duodenal lumen remains the favored theory, compared with intrauterine vascular ischemia.
During the third week of embryonic development, the second portion of the duodenum, at the junction of the foregut and midgut, forms biliary and pancreatic buds, which are derived from endoderm. During the next 4 weeks, these buds differentiate into the hepatobiliary system, with the development and subsequent fusion of the 2 pancreatic anlagen. Concurrently, the epithelium of the duodenum undergoes active proliferation, which, at times, completely obliterates the duodenal lumen. Vacuolization, followed by recanalization, reestablishes the hollow viscus.
The second part of the duodenum is the last to recanalize. The early forming biliary system consists of 2 channels arising from the embryonic duodenum. This structure creates a narrow segment of bowel, approximately 0.125 mm in length, that is interposed between the 2 biliary channels. This narrow region is the area most prone to problems, with recanalization and with atresia formation. The ampulla of Vater usually is immediately adjacent to or traverses the medial wall of the diaphragm. The presence of a bifid biliary system, or the insertion of 1 duct above the atresia and 1 duct below it, is rare, occurring when both biliary duct anlagen remain patent. The presence of bile above and below the atresia indicates a bifid biliary system.
Frequency
United States The incidence of duodenal atresia is 1 per 6000 births. Intrinsic congenital duodenal obstruction constitutes two thirds of all congenital duodenal obstructions (duodenal atresia, 40-60%; duodenal web, 35-45%; annular pancreas, 10-30%; duodenal stenosis, 7-20%).
International The incidence in Finland of congenital obstruction (intrinsic, extrinsic, combined) is 1 per 3400 live births.
Mortality/Morbidity
If duodenal atresia or significant duodenal stenosis is left untreated, the condition rapidly becomes fatal as a result of electrolyte loss and fluid imbalance.
One half of the neonates with duodenal atresia or stenosis are born prematurely.
Hydramnios occurs in approximately 40% of neonates with duodenal obstruction.
Duodenal atresia or duodenal stenosis is most commonly associated with trisomy 21. About 22-30% of patients with duodenal obstruction have trisomy 21. Other problems associated with trisomy 21 include cardiac defects (most commonly ventricular septal defects and endocardial defects), as well as Hirschsprung disease.
Race
No racial predilection exists.
Sex
The incidence of duodenal atresia and duodenal stenosis is approximately equal in males and females.
Age
Infants with duodenal atresia present with vomiting in their first few hours of life, but patients with duodenal stenosis present at various ages. The clinical findings depend on the degree of stenosis. Occasionally, with duodenal web or duodenal stenosis, presentation occurs in adulthood.
Anatomy
In most cases, duodenal atresia occurs below the ampulla of Vater. In a very few cases, the atresia occurs proximal to the ampulla.
Presentation
Bile-stained vomit in neonates aged 24 hours or younger is the typical presentation of atresia or severe stenosis. Minimal duodenal obstruction in mild stenosis or duodenal membrane may have few symptoms. In a few cases, the atresia is proximal to the ampulla of Vater and the vomit is free of bile.Both duodenal anomalies can be associated with other GI and biliary tract abnormalities (malrotation, esophageal atresia, ectopic anus, annular pancreas, gallbladder or biliary atresia, vertebral anomalies). In addition, duodenal atresia can be associated with a duodenal diaphragm, as well as with congenital abnormalities in other systems. Examples include VATER (vertebral defects, anal atresia, tracheoesophageal fistula with esophageal atresia, radial and renal anomalies) association and VACTERL (vertebral, anal, cardiac, tracheal, esophageal, renal, limb) syndrome.Anomalies of the kidneys can occur in VATER association; the most common of these renal abnormalities include aplasia, dysplasia, hydronephrosis, ectopia, persistent urachus, vesicoureteral reflux, and ureteropelvic obstruction.
A few familial cases have been reported.
Preferred Examination
Plain radiographs that demonstrate a double-bubble appearance with no distal gas are characteristic of duodenal atresia. Distal bowel gas indicates stenosis, incomplete membrane, or a hepatopancreatic ductal anomaly. Occasionally, a radiograph must be obtained with the patient in the erect or the decubitus position to delineate the duodenal component. If a combination of esophageal atresia and duodenal atresia is present, ultrasonography is preferred.
Limitations of Techniques
No oral contrast materials are necessary in the evaluation of complete duodenal obstruction. Occasionally, a small amount of positive contrast material can be instilled through a feeding tube into the distal stomach and duodenum to differentiate the diaphragm from a long stenosis.
Occasionally, barium enema examination is suggested as an adjunct study in the evaluation of duodenal atresia. Barium enema findings can demonstrate a malpositioned cecum, but this is not always diagnostic of malrotation and volvulus. In addition, if a microcolon is demonstrated, the presence of additional, more distal atresias can be suggested. Succus entericus may be prevented from reaching the colon because of the additional area of bowel obstruction. Multiple atresias are present in approximately 15% of patients. However, most surgeons can determine the presence of malrotation and additional atresias at the time of surgery.
