Teaching Case

A 3-day-old baby was presented with failure to pass meconium and abdominal distension.

This full-term baby was born by normal vaginal delivery, and his weight birth was 3200 g. The prenatal sonographic examinations were found to be normal, and there was no family history. This newborn was presented with failure to pass meconium and abdominal distension. A supine abdominal radiograph was taken, which showed the presence of multiple dilated large and small bowel loops. Gas was absent in the rectum. A nonionic iso-osmolar water-soluble enema showed a transition zone between the narrow and the dilated portions of the descending colon in the shape of an inverted cone.

The causes of neonatal lower intestinal obstruction include imperforate anus, meconium plug syndrome, meconium ileus, Hirschsprung's disease, small left colon syndrome, megacystis-microcolon-intestinal hypoperistalsis syndrome, and colonic atresia or stenosis. The histopathologic basis to assert the diagnosis of Hirschsprung's disease is the absence of ganglion cells in the myenteric plexus. This results in a narrowed aganglionic segment with a proximal dilated colon. The myenteric ganglion cells arise from the neural crest and migrate cephalo-caudally along the vagal trunks through the intestines. An early arrest in the migration between the 7th and 12th weeks of gestation leads to Hirschsprung's disease and can affect a variable length of the colon and the small bowel. The incidence of Hirschsprung's disease is one per 5,000 live births. Hirschsprung's disease occurs three to four times more often in boys and, for unknown reasons, is rare in premature infants. During the neonatal period, 80% of the patients exhibit symptoms including delay in the passage of meconium, abdominal distention, constipation, and bilious vomiting. Complications of Hirschsprung's disease include enterocolitis and perforation of the bowel (colon, appendix, or ileon). Retrograde opacification is contraindicated in patients with clinical signs of fulminant enterocolitis or signs of perforation on abdominal radiographs. The key radiologic examination in those infants is the water-soluble contrast medium enema. The most reliable radiographic sign of Hirschsprung’s disease is the presence of a gradual transition zone between the abnormal and the normal bowel. The transition zone is found in 65% infants in the rectosigmoid or sigmoid colon with a rectosigmoid caliber ratio less than 1, 14% in the descending colon, 8% in the rectum, and 10% in a more proximal segment of the large bowel. The patient should not have any prior cleansing enema prior to radiographic studies, as it may interfere with the demonstration of the transition zone. As soon as the transition zone has been detected, the examination should be discontinued as filling of the dilated bowel may lead to impaction. The transition zone is seen in approximately 80% of the infants. The diagnosis is unequivocal in only 50% of them during the first week of life. In dubious cases, delayed radiographs may be helpful in evaluating the evacuation of contrast material. The post-evacuation images may also show a transition zone, which had not been shown by the initial radiographs. Contrast medium trapping is not specific but it may be the only sign of Hirschsprung's disease in total colonic aganglionosis. A false positive transition zone at the splenic flexure may be seen in neonates who have small left colon syndrome. The other radiographic findings include denervation hyperspasticity (narrowing) of the distal segment with a sawtooth configuration due to muscular contractions, microcolon, and bowel shortening. In addition to the contrast-enhanced enema, a rectal manometry has to be performed. This examination usually shows the absence of rectoanal inhibitory reflex. If both studies confirm the disease, a mucosal rectal biopsy is not necessary before surgery. This child successfully underwent surgical resection of the denervated segment.