Jejunoileal atresia and stenosis are among the most common causes of neonatal intestinal obstruction. Atresia is a complete obstruction of the lumen of the bowel. It is far more common than stenosis or partial luminal obstruction. These lesions can occur anywhere in the small bowel but are most common in the proximal jejunum or distal ileum, where they account for 31% and 36% of cases, respectively (Robertson et al., 1994). In addition, multiple atresias of the small bowel are found in 6% of cases (deLorimier et al., 1969). These conditions are thought to result from intrauterine vascular accidents such as volvulus, intussusception, internal hernia, or vascular constriction (Louw and Barnard, 1955). In utero vascular compromise as a cause of intestinal atresias was first suspected because of associated volvulus, intussusceptions, constriction at the abdominal wall defect in gastroschisis, and kinking of bowel that were often found in association with intestinal atresias. This was supported by experimental work by Louw and Barnard (1955), who were able to replicate the pathophysiology of small intestinal atresias in animals by in utero ligation of mesenteric vessels.

The bowel lumen distal to an atresia contains bile (bile is first seen at 11 weeks of gestation), planocellular epithelium (first seen at 12 weeks), and lanugo (first seen at 6–7 months), which suggests that a vascular accident occurred well after organogenesis was complete (Romero et al., 1988). In keeping with the theory of a mesenteric vascular accident, the incidence of associated chromosomal and extraintestinal anomalies associated with jejunoileal atresia is quite low. In addition to sporadic occurrence of jejunoileal atresias, they have also been reported as a complication of amniocentesis (Richwood, 1977; Swift et al., 1979; Therkelson and Rohder, 1981). Intussusception had been considered to be a rare cause of vascular disruption resulting in atresia (Nixon and Tawes, 1971; Dalla Vecchia et al., 1998). Komuro and colleagues suggest that antenatal intussusception with or without associated volvulus may be a more important etiology of small bowel atresia than has been previously recognized (Komuro et al., 2004). In a single institution’s review of 48 newborns with small bowel atresia, this group found evidence of intussusception in 12 and volvulus in 13 cases at the time of surgery. They noted that neither intussusception nor volvulus was observed in cases of high jejunal atresia, apple peel deformity, or multiple atresias.

The most useful and commonly accepted classification of intestinal atresias is that proposed by Louw and Barnard in 1955, with numerous subsequent modifications (Figure 73-1). Type I atresias have an intraluminal diaphragm in continuity with the muscular coats of the proximal and distal segments; they account for 32% of cases. Type II atresias have a fibrotic cord connecting the two blind-ending bowel segments with an intact mesentery; they account for 25% of cases. Type III atresias are divided into those with complete separation of the blind-ending loops of bowel with a U-shaped mesenteric defect (type IIIa); they comprise 15% of cases. The other, type IIIb atresia, is associated with an extensive mesenteric defect and an associated “apple peel” deformity. The terminal ileum is perfused in a retrograde fashion from a single ileocolic artery around which the distal ileum coils, giving the appearance of an apple peel. Although these are unusual atresias, accounting for only 11% of cases, they are frequently seen in extremely premature infants and result in significant shortening of bowel length and the short-bowel syndrome (Dickson, 1970). They may also recur in families. Type IV lesions are multiple atresias of the small intestine and account for 6% to 17% of cases.

When associated anomalies occur in jejunoileal atresia, they generally involve the gastrointestinal tract. While the incidence of extragastrointestinal anomalies is very low, other gastrointestinal anomalies may be seen in up to 45% of patients. These abnormalities include malrotation (23%), intestinal duplications (3%), microcolon (3%), and esophageal atresia (3%) (deLorimier et al., 1969; Nixon and Tawes, 1971). Meconium ileus and meconium peritonitis occur in 12% and 8% of cases, respectively. Associated cardiac and chromosomal anomalies are rare (Rescorla and Grosfeld, 1985) (Table 73-1).

Meconium ileus may be the underlying cause of jejunoileal atresia in infants with cystic fibrosis, who have signs of prenatal volvulus or meconium peritonitis as a result of small-bowel perforation. The incidence of meconium ileus is 20% in most series of jejunoileal atresia (Santulli et al., 1970). For this reason, cystic fibrosis mutation testing or sweat chloride analysis is advisable for all cases of jejunoileal atresia. Gastroschisis is also associated with jejunoileal atresia and is thought to be due to ischemic injury to the bowel from constriction at the abdominal wall defect (see Chapter 63).

It has been also observed that there is an association between small-bowel atresia, particularly multiple atresia and placental vascular abnormalities (Komuro et al., 2004b). In a small series of 48 cases, 4 infants had significant abnormalities associated with either apple peel abnormality or multiple intestinal atresia. The placental abnormalities included marginal cord insertion, placental infarction, calcification, and cyst formation. In contrast to most cases of jejunoileal atresia, these cases were associated with extragastrointestinal abnormalities including brain, ophthalmic, and skeletal anomalies (Komuro et al., 2004b).

Jejunoileal atresias occur relatively commonly, with approximately 1 case in every 3000 livebirths. However, the incidence of intestinal atresia has been reported to range from 1 in 400 to 1 in 5000 livebirths, with boys and girls affected equally (Touloukian, 1993). This anomaly is about twice as common as esophageal atresia and three times more common than Hirschsprung’s disease (Rowe et al., 1995).

The only abdominal structures that normally contain fluid are the stomach and gallbladder, and these are readily visible on prenatal ultrasound examination (Goldstein et al., 1987). Swallowing of amniotic fluid begins at approximately 16 weeks of gestation, and meconium accumulates in the small bowel and colon throughout the second and third trimesters. The diagnosis of obstruction before 18 weeks of gestation is uncommon, and it remains difficult to detect up to 24 weeks. The bowel becomes progressively more visible and peristalsis can be seen with increasing gestational age. The meconium-filled lumen becomes increasingly echogenic as compared with the hypoechogenic muscular wall. Dilated loops of bowel with an internal diameter greater than 7 mm should be considered abnormal and may suggest obstruction (Nyberg et al., 1987). Proximal gastrointestinal obstruction often leads to polyhydramnios, which occurs in 0.4% to 1.5% of pregnancies (Wallenburg and Wladimoroff, 1977). Up to 63% of fetuses with jejunoileal atresia associated with polyhydramnios have additional anomalies, one-third of which involve the gastrointestinal tract (Damato et al., 1993).

Some authors have suggested that the association of polyhydramnios and dilated loops of bowel are markers of more severe bowel obstruction with a larger need for parenteral nutrition and longer predicted length of stay (Iacobelli et al., 2006). In this group’s experience, the presence of dilated loops and polyhydramnios were more likely to result in disproportional size of proximal and distal loops of bowel, making delayed anastomosis more likely. This information should be incorporated into prenatal counseling (Basu and Burge, 2004; Iacobelli et al., 2006).

Jejunal obstruction may be visualized on prenatal ultrasound examination by the presence of fluid-filled loops and bowel demonstrating increased peristalsis (Figure 73-2). Floating particulate matter may also be observed (Kirkinen and Jouppila, 1984). The abdomen may appear distended, and in the case of meconium ileus, increased bowel echogenicity can be present (Muller et al., 1984). Polyhydramnios occurs in approximately 25% of cases and is seen more commonly in cases of proximal obstruction. Polyhydramnios may be absent in proximal stenosis or very distal obstruction, where adequate absorption of swallowed amniotic fluid occurs. The extent of bowel dilation and mural thickening may correlate with the presence of obstruction. The incidence of obstruction increases significantly when the bowel diameter is greater than 17 mm. Similarly, the incidence of obstruction is approximately 40% with a mural thickness of greater than 3 mm (Langer et al., 1993). Visualization of increased peristalsis associated with bowel dilatation increases the likelihood of obstruction.

In recent years, magnetic resonance imaging has been used more commonly to characterize gastrointestinal anomalies (Quinn et al., 1998; Shinmoto et al., 2000; Ertl-Wagner et al., 2002; Saguintaah et al., 2002). The utility of MRI is in not only characterizing gastrointestinal tract abnormalities but also in demonstrating normal bowel close to an intra-abdominal cyst (Veyrac et al., 2004) MRI is best used as an adjunct to ultrasound examination or in combination with amniotic fluid enzyme analysis (Garel et al., 2006). MRI may be informative in evaluating sonographically detected bowel dilatation or echogenic bowel (Carcopino et al., 2007).