Failure to Pass Meconium: Diagnosing Neonatal Intestinal Obstruction

Author: Vera Loening-Baucke, Ken Kimura
Date: Nov 1, 1999

Timely passage of the first stool is a hallmark of the well-being of the newborn infant. Failure of a full-term newborn to pass meconium in the first 24 hours may signal intestinal obstruction. Lower intestinal obstruction may be associated with disorders such as Hirschsprung's disease, anorectal malformations, meconium plug syndrome, small left colon syndrome, hypoganglionosis, neuronal intestinal dysplasia and megacystis- microcolon-intestinal hypoperistalsis syndrome. Radiologic studies are usually required to make the diagnosis. In addition, specific tests such as pelvic magnetic resonance imaging, anorectal manometry and rectal biopsy are helpful in the evaluation of newborns with failure to pass meconium. (Am Fam Physician 1999;60:2043-50.)

The first stool is passed within 24 hours of birth in 99 percent of healthy full-term infants and within 48 hours in all healthy full-term infants.1 Failure of a full-term newborn to pass meconium within the first 24 hours should raise a suspicion of intestinal obstruction. Among premature infants, however, one study2 revealed that only 37 percent of 844 preterm infants passed their first stool in the first 24 hours; 32 percent had delayed passage of the first stool beyond 48 hours. In 99 percent of the preterm infants, the first stool was passed by the ninth day after birth.

Clinical Presentation of Meconium Retention

Failure to pass meconium combined with progressive abdominal distention, refusal to feed and vomiting of bilious intestinal contents are the classic clinical signs of intestinal obstruction in neonates. Abdominal examination often reveals distended loops of bowel, which may be visible or palpable. Anal inspection is essential to exclude the presence of anal atresia, perineal fistula with anal atresia, the membranous form of anal atresia and anal stenosis.

Plain radiographs of the abdomen do not allow differentiation of small bowel obstruction from large bowel obstruction. The differential diagnosis for small bowel obstruction in neonates includes duodenal atresia, malrotation and volvulus, jejunoileal atresia, meconium ileus and meconium peritonitis. Bilious vomiting, with or without abdominal distention, is usually the first sign of small bowel obstruction. The differential diagnosis for large bowel obstruction in neonates includes Hirschsprung's disease, anorectal malformations and meconium plug syndrome (Table 1).

In many cases of suspected neonatal intestinal obstruction, the clinical history and physical examination combined with plain abdominal radiographs, contrast enema radiographic examination, anorectal manometry and rectal biopsy eventually yield the diagnosis. The most difficult management decision is to decide between conservative management and emergency surgery. Ideally, all newborns suspected of having bowel obstruction should receive treatment at a center where a pediatric surgeon is available.

Illustrative Case

A 3,480 g (7 lb, 7 oz) male infant was born after 40 weeks' gestation. There were no complications during the pregnancy and delivery. He did not pass meconium after birth, and he had the onset of vomiting on the first day. His abdomen became mildly distended. The infant was not able to feed, and abdominal distention increased.

Rectal examination revealed a tight anus. On the second day, flat and upright abdominal films demonstrated numerous loops of dilated bowel (Figure 1a). Barium enema radiographic examination showed that most of the dilated bowel was colon; no transition zone was seen (Figure 1b).

The surgeon performed an anal dilatation, and the infant subsequently passed gas and meconium, which was followed by resolution of all symptoms.

After discharge from the hospital, the infant's mother continued performing periodic anal dilatation because he had difficulties moving his bowel. Digital rectal examination by the physician when the infant was five weeks of age revealed a tight anus and liquid stool but no impaction.

One week later, the mother noticed a bloody ring around his bowel movements. Barium enema radiographic examination at this time showed a transition zone in the distal portion of the sigmoid colon, with marked dilatation of the descending colon and left side of the transverse colon (Figure 1c). Anorectal manometry showed an absent rectosphincteric reflex. No ganglion cells were seen in the rectal biopsy. These findings were consistent with Hirschsprung's disease.

Hirschsprung's Disease

Hirschsprung's disease, or congenital aganglionic megacolon, has an overall incidence of one in 4,000 live births.3 It accounts for 20 to 25 percent of the cases of neonatal bowel obstruction.4 The disease affects four times as many boys as girls, and 8 percent of patients with Hirschsprung's disease also have Down syndrome.5 The abnormal bowel innervation affects the internal anal sphincter. Most often, the rectosigmoid is involved, but a variable length of gut can be involved. A 30-year retrospective study6 revealed that the mean age at diagnosis has decreased to 2.6 months because of vigilance on the part of physicians, the use of anorectal manometry for assessment of the anal sphincter and early rectal biopsy to confirm the clinical diagnosis.

A common presentation of Hirschsprung's disease in the newborn is failure to pass meconium during the first few days of life, with subsequent passage of a meconium plug followed by sparse bowel movements. Gastrointestinal bleeding and diarrhea are danger signs for Hirschsprung's disease- associated enterocolitis. Enterocolitis can be fatal and is thought to be due to proliferation of bacteria as a result of stasis.

Physical examination often reveals the anus and rectum to be narrow and empty of stool. Plain abdominal radiographs show gas and stool in the colon and often the distention with stool or gas does not reach distally to the pelvic rim (Figure 1a).

Barium enema radiographic examination, performed with the colon unprepared, may reveal a transition zone that separates the small- to normal-diameter aganglionic bowel from the dilated bowel above (Figure 1c). A transition zone may not be recognizable in up to 25 percent of neonates with classic Hirschsprung's disease (Figure 1b). Similarly, a transition zone may not be discernible in patients with ultrashort-segment Hirschsprung's disease, in patients with total colonic aganglionosis in whom the transition zone is above the colon and in patients who had an emergency colostomy. The presence of barium in the 24-hour delayed film is also suggestive of Hirschsprung's disease.

Anorectal Manometry

When possible, anorectal manometry should be performed in all newborns with symptoms of lower bowel obstruction. With anorectal manometry, changes in anal pressure are recorded during and after rectal distention. When ganglion cells are present, rectal distention with a balloon inhibits the internal anal sphincter, resulting in a fall in anal pressure, called the rectosphincteric reflex (Figure 2a). In patients with Hirschsprung's disease, the rectosphincteric reflex is absent (Figure 2b ).

Anorectal manometry is most helpful in excluding the diagnosis of Hirschsprung's disease in a newborn.7,8 If the rectosphincteric reflex is absent, the diagnosis of Hirschsprung's disease needs to be confirmed by rectal suction biopsy, which shows no ganglion cells and markedly increased acetylcholinesterase staining of increased coarse neural fibers within the muscularis mucosae and the lamina propria.


Surgery to remove or bypass the diseased bowel is required in all children with Hirschsprung's disease. In most neonates, a colostomy is initially placed into the normal bowel for decompression, followed by corrective surgery in three to six months. Occasionally, a primary pull-through procedure is performed.

Meconium Plug Syndrome

Meconium plug syndrome is the mildest and most common form of functional distal obstruction in the newborn. 9 It is a transient form of distal colonic or rectal obstruction caused by inspissated, immobile meconium. The incidence of meconium plug syndrome is estimated to range from one case in 500 to one case in 1,000 neonates.10 The etiology of this disorder is unclear.

Another rare cause of neonatal intestinal obstruction is the megacystis- microcolon-intestinal hypoperistalsis syndrome.22 In this disorder, the small bowel is dilated and shortened, and the colon is a microcolon (Figure 7). There is an abundance of ganglion cells in the entire gastrointestinal tract. All patients with this syndrome have megacystis and megaureters, and most eventually die of complications from the disorder.


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table 1Differential Diagnosis of Conditions That May Be Associatedwith Failure to Pass Meconium in the NewbornDiagnosis Frequency Abnormal findings TherapyHirschsprung's 1/4,0003 Tight anus, empty Surgerydisease rectum, transition zoneMeconium plug 1/500 to Meconium plugs Rectal stimulation,syndrome 1/1,00010 enemaMeconium ileus 1/2,80012 Abdominal distention Enema with at birth, cystic intravenous fibrosis fluids, surgeryAnorectal 1/4,000 to Absent anus, tight Dilatation, surgerymalformation 1/8,00014 anus or fistulaSmall left colon Rare Transition zone* at Enema, rarely,syndrome splenic flexure colostomyHypoganglionosis Rare Transition zone* Medical, TPN, surgeryNeuronal intestinal Rare Transition zone,* Medical, surgerydysplasia type A mucosal inflammationNeuronal intestinal Rare Megacolon Medical, rarely,dysplasia type B surgeryMegacystis-microcolon- Very rare Microcolon, TPNintestinal megacystishypoperistalsissyndromeTPN = total parenteral nutrition.*-Transition zone (from small- to large-diameter bowel) refers toradiographic visualization on contrast study.

The Authors VERA LOENING-BAUCKE, M.D., is professor of pediatrics at the University of Iowa School of Medicine, Iowa City. She has a special clinic for children with defecation disorders. Her research interests are anorectal physiology in children with defecation disorders and the study of the afferent pathways from the rectum to the brain. KEN KIMURA, M.D., is professor of pediatric surgery at the University of Iowa School of Medicine, Iowa City. He has special interests in children with Hirschsprung's disease and short bowel syndrome. He has developed surgical procedures for both diseases. Address correspondence to Vera Loening-Baucke, M.D., Department of Pediatrics, University of Iowa Hospitals and Clinics, JCP 2555, 200 Hawkins Dr., Iowa City, IA 52242. Reprints are not available from the authors.

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