Ileal atresia

The diagnosis is usually apparent on the plain films. The abdominal radiograph shows a few dilated bowel loops (three or four air bubbles), more than in the case of duodenal atresia and fewer than in ileal atresia or in other causes of low bowel obstruction (Fig. 1.14). The loop just proximal to the site of the atresia is frequently disproportionately dilated with a bulbous end. There is no air in the lower portion of the abdomen this is observed most clearly in the upright film (Rathaus and Grunebaum 1992) (Fig. 1.15). The colon cannot be identified and air... 

For practical purposes, the differential diagnosis of low intestinal obstruction in the neonate consists of five conditions. Two conditions involve the distal ileum and include ileal atresia and meconium ileus, and three involve the colon, which are colonic atresia, Hirschsprung s disease, and functional immaturity of the colon that includes meconium plug... 

Fig. 1.18a,b. High intestinal obstruction, a Plain radiograph of a newborn infant that shows an airless abdomen with air only in the stomach. Despite the lack of intestinal air, there is distension of the flanks and elevation of the diaphragms, b Sonography demonstrates the abdominal distension to be produced by fluid-filled intestinal loops. At surgery, a proximal ileal atresia was found... 

Ileal atresia is an important cause for low intestinal obstruction. It represents approximately 50% of small bowel atresias and the etiology is similar to that of jejunal atresia. As jejunal atresias, they are believed to result from an intrauterine vascular injury. Approximately 25% have a history of polyhydramnios (Sweeney et al. 2001). 

Plain film shows numerous dilated loops of bowel occupying the entire abdominal cavity, including the pelvic portion, and multiple air-fluid levels in upright film (Fig. 1.19). With this degree of distension the mucosal pattern of the small bowel is effaced and it is impossible to differentiate the small bowel from the colon (Winters et al. 1992). Examination of the colon is then warranted to disclose the presence or absence of a colonic lesion. In ileal atresia, the colon is normally placed but has an abnormally small caliber, the so-called functional microcolon typical of distal small bowel obstruction (Dalla Vecchia et al. 1998) (Fig. 1.19d,e). The presence of pneumoperitoneum indicates that perforation has occurred and a colon examination is contraindicated. Intraperitoneal calcifications, indicative of meconium peritonitis, are not uncommon in ileal atresia. 

Fig. 1.19a-e. Ileal atresia, a-c Supine, lateral, and upright abdominal radiographs show multiple dilated air-filled bowel loops occupying the entire abdominal cavity, with air-fluid levels in the upright radiograph. Note in (b) the absence of air in the rectum. With this degree of distension it is impossible to differentiate the small bowel from the colon. d,e Contrast enema outlines the minute size of the colon corresponding to an unused colon... 

Fig. 1.21a,b. a Neonate with cystic fibrosis. Sonography shows intestinal loops filled with hyperechogenic and thick meconium. b Neonate with ileal atresia. Intestinal loops are filled with hypoechoic fluid and air... 

Fig. 1.26. Meconium peritonitis with intrauterine bowel perforation. Free air within the peritoneal cavity is observed (arrows) in this neonate with ileal atresia. No bowel distension is observed. A patent bowel perforation was found at surgery...

The radiological diagnosis of obstruction is usually visible on the conventional (plain) radiograph. In uncomplicated cases these radiographs of the abdomen are sufficient. The pre-atretic intestinal loops are dilated because of accumulation of large amounts of fluid and fluid levels are usually present on horizontal beam films. In case of jejunal atresia only a few loops of distended jejunum are present in the left upper abdomen, while in ileal atresia many dilated loops are identified. In complicated cases, especially with an abnormally distended and painful abdomen, a colon enema or US can be useful- particularly from the differential diagnostic point of view to exclude meconium ileus or meconium peritonitis. In case of atresia, a microcolon without the presence of meconium is usually found (Devos and Meradji 2003). 

In ultra-short segment Hirschsprung s disease the barium enema may show a large mega-rectum but no other specific findings. In NID, chronic intestinal pseudo-obstruction and total colonic agangiionosis the barium enema is often non-contributory. However, total colonic agangiionosis may sometimes have the appearance of a microcolon and therefore needs to be differentiated form ileal atresia and meconium ileus. 

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