Duodenal atresia, or stenosis, is a leading cause of intestinal obstruction in newborns and one of the most common gastrointestinal anomalies that can be diagnosed prenatally. A commonly held developmental theory is that at 1 month of gestation, the lumen of the duodenum is thought to be obliterated by proliferating epithelium. This solid core of epithelium undergoes vacuolization and recanalization, restoring the lumen. Failure of recanalization of the solid stage is thought to result in duodenal atresia or stenosis. Atresia is more common than stenosis and occurs in approximately 70% of cases (Boyden et al., 1967; Skandalakis et al., 1994). Skandalakis et al. (1994) have described 3 types of duodenal atresia. The most common duodenal anomaly (69% of cases) is membranous mucosal atresia (type I) with an intact muscular wall. The proximal duodenum is ballooned out while the duodenum distal to the atresia is narrowed. This mucosal membrane may take on the shape of a “wind sock” because of peristalsis and increased proximal intraluminal pressure (Rowe et al., 1968). The origin of the wind-sock membrane is usually intimately associated with the ampulla of Vater. A type II duodenal atresia is rare (2% of cases) and has a short fibrous cord connecting the two ends of the atretic duodenum. Type III duodenal atresia has a complete separation between the two ends of the duodenum and can be associated with biliary tract anomalies in 6% of cases (Reid, 1973a and b; Jona and Berlin et al., 1976; Paine and Noblett, 1977; Knechtle and Filston, 1990). Duodenal stenosis accounts for the remaining 23% of cases. These anatomic relations are rarely evident sonographically. An annular pancreas occurs in 20% to 30% of patients with duodenal atresia or stenosis (Fonkalsrud et al., 1969; Reid, 1973a and b; Wesley and Mahour, 1977). The developmental relationship between annular pancreas and duodenal atresia and stenosis is unclear.

An annular pancreas can produce extrinsic compression and result in stenosis, but it is more commonly associated with an intrinsic obstruction due to complete atresia (Merrill and Raffensperger, 1976).

Duodenal stenosis or atresia occurs in approximately 1 in 10,000 livebirths (Fonkalsrud et al., 1969; Forrester and Merz, 2004).

Prenatal sonographic diagnosis of duodenal obstruction has been made as early as 20 weeks of gestation (Hancock and Wiseman, 1989). The majority of cases, however, are not diagnosed until the third trimester. The most common indication for sonography is uterine size greater than dates because of polyhydramnios, which is present in up to 53% of cases (Girvan and Stephens, 1974; Farrant et al., 1981). Prenatal sonography may show the characteristic “double bubble” sign (Figure 72-1) that represents the dilated fluid-filled stomach and proximal duodenum (Balcar et al., 1984; Langer et al., 1989). Although occasionally seen earlier, duodenal atresia is not usually diagnosed prior to 24 weeks of gestation. If the fetus has recently vomited (Figure 72-2), or in cases of stenosis in which sufficient amounts of amniotic fluid pass the obstruction, these features may be subtle or absent (Bowie and Clair, 1982). If the diagnosis of duodenal atresia or stenosis is suspected, serial ultrasound examination may be required to prove the diagnosis. Because 30% of patients with duodenal atresia will have trisomy 21, other sonographic features of Down syndrome should be sought, including nuchal fold thickening, hypomineralization of fifth finger middle phalanx (clinodactyly), and elevated biparietal diameter and fetal length ratio (Lockwood, 1993), (see Chapters 2 and 3).

MRI has been used as an adjunct to ultrasound examination in the diagnosis of duodenal atresia. On T2-weighted sequences, the fluid within the stomach and duodenum will appear hyperintense and the post atretic bowel will have normal size bowel loops. The bowel produces sufficient secretions to yield a normal appearance by MRI (Veyrac et al., 2004).

A persistently dilated fluid-filled fetal duodenum is always abnormal and should raise the suspicion of possible duodenal atresia or stenosis. This can be a difficult diagnosis to make prior to 24 weeks of gestation (Nelson et al., 1982; Bovicelli et al., 1983). The differential diagnosis, in addition to duodenal atresia or stenosis, should include annular pancreas, malrotation with either obstructing Ladd’s bands or midgut volvulus, gastric or duodenal duplications, and preduodenal portal vein. Isolated duodenal stenosis may be indistinguishable from annular pancreas with associated duodenal stenosis until surgical exploration. Malrotation may give a similar “double bubble” appearance but, unlike atresia, there will be some amniotic fluid in loops beyond the duodenum. Ladd’s bands may partially obstruct the duodenum, mimicking duodenal stenosis. One sonographic clue to midgut volvulus is the reversed relation of the superior mesenteric vein and artery by Doppler ultrasound study, in which the superior mesenteric vein appears anterior to the superior mesenteric artery. Large gastric or duodenal duplications can be indistinguishable from duodenal atresia (Figure 72-3) (Malone et al., 1997). Anomalous development of the paired embryonic vitelline veins contributes to the myriad complex anatomic defects of this region. Persistence of a primitive vitelline vein results in an anterior or preduodenal portal vein that passes over the pancreas and third portion of the duodenum, which can partially obstruct the duodenum.

More than half of the fetuses with duodenal atresia have associated anomalies. Trisomy 21 is the most frequently associated condition, occurring in 27% to 34% of cases (Fonkalsrud et al., 1969; Nixon and Tawes, 1971; Reid, 1973a and b; Girvan and Stephens, 1974; Davey, 1980; Hancock and Wiseman, 1989) (Table 72-1). In several large series, congenital heart disease was also commonly associated, occurring in 17% to 33% of cases (Fonkalsrud et al., 1969; Nixon and Tawes, 1971; Reid, 1973a and b; Girvan and Stephens, 1974; Davey, 1980; Hancock and Wiseman, 1989). The most common cardiac lesions encountered are atrial or ventricular septal defect. Other anomalies associated with duodenal atresia include malrotation, annular pancreas, esophageal atresia, tracheoesophageal fistula, and genitourinary and anorectal malformations. Numerous pancreatic and biliary anomalies have been reported in association with duodenal atresia and stenosis. These include biliary atresia, choledochal cyst, pancreatic lipomatosis, pancreas divisum, and persistent dual biliary duct drainage to duodenum proximal and distal to the atresia. Unusual biliary duct anomalies that occur in association with duodenal atresia are seen in infants with type III defects. The association of congenital anomalies with maternal and gestational and preexisting diabetes (Schaefer-Graf et al., 2000) is also thought to increase the frequency of duodenal atresia (Ozturk et al., 2007). Adeyemi (1988) has identified an association between duodenal atresia, partial situs inversus, and right-sided diaphragmatic hernia through the foramen of Bochdalek. This is an extremely rare condition known as multiple organ malrotation syndrome (MOMS) (Adeyemi, 1988).