Congenital duodenal obstruction occurs in 2.5-10/100,000 live births. In most cases, it is caused by atresia, an intrinsic defect of bowel formation. It can also result from extrinsic compression by abnormal neighboring structures (e.g., annular pancreas, preduodenal portal vein), duplication cysts, or congenital bands associated with malrotation. Although intrinsic and extrinsic causes of duodenal obstruction occur independently, they can also coexist. Thus, a high index of suspicion for more than one underlying etiology may be critical to avoiding unnecessary reoperations in these infants.

Duodenal atresia complicates 1/10,000 live births and accounts for 25-40% of all intestinal atresias. In contrast to more-distal atresias, which likely arise from prenatal vascular accidents, duodenal atresia results from failed recanalization of the intestinal lumen during gestation. Throughout the 4th and 5th weeks of normal fetal development, the duodenal mucosa exhibits rapid proliferation of epithelial cells. Persistence of these cells, which should degenerate after the 7th week of gestation, leads to occlusion of the lumen (atresia) in approximately two thirds of cases and narrowing (stenosis) in the remaining one third. Duodenal atresia can take several forms, including a thin membrane that occludes the lumen, a short fibrous cord that connects 2 blind duodenal pouches, or a gap that spans 2 nonconnecting ends of the duodenum. The membranous form is most common, and it almost invariably occurs near the ampulla of Vater. In rare cases, the membrane is distensible and is referred to as a windsock web. This unusual form of duodenal atresia causes obstruction several centimeters distal to the origin of the membrane.

Approximately 50% of infants with duodenal atresia are premature. Concomitant congenital anomalies are common and include congenital heart disease (30%), malrotation (20-30%), annular pancreas (30%), renal anomalies (5-15%), esophageal atresia with or without tracheoesophageal fistula (5-10%), skeletal malformations (5%), and anorectal anomalies (5%). Of these anomalies, only complex congenital heart disease has been associated with increased mortality. Annular pancreas has been associated with increased late complications, including gastroesophageal reflux disease, peptic ulcer disease, pancreatitis, gastric outlet and recurrent duodenal obstruction, and gastric cancer. Thus, long-term follow-up of these patients into adulthood is warranted. Nearly half of patients with duodenal atresia have chromosome abnormalities; trisomy 21 is identified in up to one third of patients.

Clinical Manifestations and Diagnosis

The hallmark of duodenal obstruction is bilious vomiting without abdominal distention, which is usually noted on the 1st day of life. Peristaltic waves may be visualized early in the disease process. A history of polyhydramnios is present in half the pregnancies and is caused by inadequate absorption of amniotic fluid in the distal intestine. This fluid may be bile stained due to intrauterine vomiting. Jaundice is present in one third of the infants.

The diagnosis is suggested by the presence of a “double-bubble” sign on a plain abdominal radiograph (Fig. 322-1). The appearance is caused by a distended and gas-filled stomach and proximal duodenum, which are invariably connected. Contrast studies are occasionally needed to exclude malrotation and volvulus because intestinal infarction can occur within 6-12 hr if the volvulus is not relieved. Contrast studies are generally not necessary and may be associated with aspiration. Prenatal diagnosis of duodenal atresia is readily made by fetal ultrasonography, which reveals a sonographic double-bubble. Prenatal identification of duodenal atresia is associated with decreased morbidity and fewer hospitalization days.

Figure 322-1 Abdominal radiograph of a newborn infant held upright. Note the “double-bubble” gas shadow above and the absence of gas in the distal bowel in this case of congenital duodenal atresia.

The primary etiologies of congenital small bowel obstruction involve intrinsic abnormalities in anatomic development (jejeunoileal stenosis and atresia), mucus secretion (meconium ileus), and bowel wall innervation (long-segment Hirschprung disease).

Jejeunoileal atresias are generally attributed to intrauterine vascular accidents, which result in segmental infarction and resorption of the fetal intestine. Underlying events that potentiate vascular compromise include intestinal volvulus, intussusception, meconium ileus, and strangulating herniation through an abdominal wall defect associated with gastroschisis or omphalocele. Maternal behaviors that promote vasoconstriction, such as cigarette smoking and cocaine use, might also have a role. Only a few cases of familial inheritance have been reported. In these families, multiple intestinal atresias have occurred in an autosomal recessive pattern. Jejunoileal atresias have been linked with multiple births, low birth weight, and prematurity. Unlike atresia in the duodenum, they are not commonly associated with extraintestinal anomalies.

Five types of jejunal and ileal atresias are encountered (Fig. 322-2). In type I, a mucosal web occludes the lumen but continuity is maintained between the proximal and distal bowel. Type II involves a small-diameter solid cord that connects the proximal and distal bowel. Type III is divided into two subtypes. Type IIIa occurs when both ends of the bowel end in blind loops, accompanied by a small mesenteric defect. Type IIIb is similar, but it is associated with an extensive mesenteric defect and a loss of the normal blood supply to the distal bowel. The distal ileum coils around the ileocolic artery, from which it derives its entire blood supply, producing an “apple-peel” appearance. This anomaly is associated with prematurity, an unusually short distal ileum, and significant foreshortening of the bowel. Type IV involves multiple atresias. Types II and IIIa are the most common, each accounting for 30-35% of cases. Type I occurs in approximately 20% of patients. Types IIIb and IV account for the remaining 10-20% of cases, with IIIb being the least common configuration.

Figure 322-2 A and B, Classification of intestinal atresia. Type I: Mucosal obstruction caused by an intraluminal membrane with intact bowel wall and mesentery. Type II: Blind ends are separated by a fibrous cord. Type IIIa: Blind ends are separated by a V-shaped mesenteric defect. Type IIIb: “Apple-peel” appearance. Type IV: Multiple atresias.

(From Grosfeld J: Jejunoileal atresia and stenosis. In Welch KJ, Randolph JG, Ravitch MM, editors: Pediatric surgery, ed 4, Chicago, 1986, Year Book Medical Publishers.)

Meconium ileus occurs primarily in newborn infants with cystic fibrosis, an exocrine gland defect of chloride transport that results in abnormally viscous secretions. Approximately 80-90% of infants with meconium ileus have cystic fibrosis, but only 10-15% of infants with cystic fibrosis present with meconium ileus. In simple cases, the distal 20-30 cm of ileum is collapsed and filled with pellets of pale stool. The proximal bowel is dilated and filled with thick meconium that resembles sticky syrup or glue. Peristalsis fails to propel this viscid material forward, and it becomes impacted in the ileum. In complicated cases, a volvulus of the dilated proximal bowel can occur, resulting in intestinal ischemia, atresia, and/or perforation. Perforation in utero results in meconium peritonitis, which can lead to potentially obstructing adhesions and calcifications.

Both intestinal atresia and meconium ileus must be distinguished from long-segment Hirschprung disease. This condition involves congenital absence of ganglion cells in the myenteric and submucosal plexi of the bowel wall. In a small subset (5%) of patients, the aganglionic segment includes the terminal ileum in addition to the entire length of the colon. Infants with long-segment Hirschprung disease present with a dilated small intestine that is ganglionated but has hypertrophied walls, a funnel-shaped transitional hypoganglionic zone, and a collapsed distal aganglionic bowel.

Clinical Manifestation and Diagnosis

Distal intestinal obstruction is less likely than proximal obstruction to be detected in utero. Polyhydramnios is identified in 20-35% of jejunoileal atresias, and it may be the first sign of intestinal obstruction. Abdominal distention is rarely present at birth, but it develops rapidly after initiation of feeds in the first 12-24 hr. Distention is often accompanied by vomiting, which is often bilious. Up to 80% of infants fail to pass meconium in the first 24 hours of life. Jaundice, associated with unconjugated hyperbilirubinemia, is reported in 20-30% of patients.

In patients with obstruction due to jejunoileal atresia or long-segment Hisrchprung disease, plain radiographs typically demonstrate multiple air-fluid levels proximal to the obstruction in the upright or lateral decubitus positions (Fig. 322-3). These levels may be absent in patients with meconium ileus because the viscosity of the secretions in the proximal bowel prevents layering. Instead, a typical hazy or ground-glass appearance may be appreciated in the right lower quadrant. This haziness is caused by small bubbles of gas that become trapped in inspissated meconium in the terminal ileal region. If there is meconium peritonitis, patchy calcification may also be noted, particularly in the flanks. Plain films can reveal evidence of pneumoperitoneum due to intestinal perforation. Air may be seen in the subphrenic regions on the upright view and over the liver in the left lateral decubitus position.

Figure 322-3 A, Abdominal radiograph in a neonate with bilious vomiting shows a few loops of dilated intestine with air-fluid levels. B, At laparotomy, a type I (mucosal) jejunal atresia was observed.

(From O’Neill JA Jr, Grosfeld JL, Fonkalsrud EW, et al, editors: Principles of pediatric surgery, ed 2, St Louis, 2003, Mosby, p 493.)

Because plain radiographs do not reliably distinguish between small and large bowel in neonates, contrast studies are often required to localize the obstruction. Water-soluble enemas (Gastrografin, Hypaque) are particularly useful in differentiating atresia from meconium ileus and Hirschprung disease. A small “microcolon” suggests disuse and the presence of obstruction proximal to the ileocecal valve. Abdominal ultrasound may be an important adjunctive study, which can distinguish meconium ileus from ileal atresia and also identify concomitant intestinal malrotation.

Malrotation is incomplete rotation of the intestine during fetal development. The gut starts as a straight tube from stomach to rectum. Intestinal rotation and attachment begins in the 5th week of gestation when the mid-bowel (distal duodenum to mid-transverse colon) begins to elongate and progressively protrudes into the umbilical cord until it lies totally outside the confines of the abdominal cavity. As the developing bowel rotates in and out of the abdominal cavity, the superior mesenteric artery, which supplies blood to this section of gut, acts as an axis. The duodenum, on re-entering the abdominal cavity, moves to the region of the ligament of Treitz, and the colon that follows is directed to the left upper quadrant. The cecum subsequently rotates counterclockwise within the abdominal cavity and comes to lie in the right lower quadrant. The duodenum becomes fixed to the posterior abdominal wall before the colon is completely rotated. After rotation, the right and left colon and the mesenteric root become fixed to the posterior abdomen. These attachments provide a broad base of support to the mesentery and the superior mesenteric artery, thus preventing twisting of the mesenteric root and kinking of the vascular supply. Abdominal rotation and attachment are completed by the 12th week of gestation.

Nonrotation occurs when the bowel fails to rotate after it returns to the abdominal cavity. The 1st and 2nd portions of the duodenum are in their normal position, but the remainder of the duodenum, jejunum, and ileum occupy the right side of the abdomen and the colon is located on the left. The most common type of malrotation involves failure of the cecum to move into the right lower quadrant (Fig. 322-4). The usual location of the cecum is in the subhepatic area. Failure of the cecum to rotate properly is associated with failure to form the normal broad-based adherence to the posterior abdominal wall. The mesentery, including the superior mesenteric artery, is tethered by a narrow stalk, which can twist around itself and produce a midgut volvulus. Bands of tissue (Ladd bands) can extend from the cecum to the right upper quadrant, crossing and possibly obstructing the duodenum.

Figure 322-4 The mechanism of intestinal obstruction with incomplete rotation of the midgut (malrotation). The dotted lines show the course the cecum should have taken. Failure to rotate has left obstructing bands across the duodenum and a narrow pedicle for the midgut loop, making it susceptible to volvulus.

(From Nixon HH, O’Donnell B: The essentials of pediatric surgery, Philadelphia, 1961, JB Lippincott.)

Malrotation and nonrotation are often associated with other anomalies of the abdominal wall such as diaphragmatic hernia, gastroschisis, and omphalocele. Malrotation is also associated with the heterotaxy syndrome, which is a complex of congenital anomalies including congenital heart malformations, malrotation, and either asplenia or polysplenia (Chapter 425.11).