Meconium ileus is most often an early manifestation of cystic fibrosis, which causes gastrointestinal secretions to be extremely viscid and adherent to the intestinal mucosa. Meconium ileus is the presenting clinical manifestation of cystic fibrosis in 10 to 20% of cases. Of infants with meconium ileus, 80 to 90% have cystic fibrosis.
Obstruction occurs at the level of the terminal ileum (unlike the colonic obstruction caused by meconium plug syndrome) and may be diagnosed by prenatal ultrasonography. Distal to the obstruction, the colon is narrow and empty or contains small amounts of desiccated meconium pellets. The relatively empty, small-caliber colon is called a microcolon and is secondary to disuse.
About 50% of cases are complicated by malrotation, intestinal atresia, or perforation. The distended loops of small bowel may twist to form a volvulus in utero. If the intestine loses its vascular supply and infarcts, sterile meconium peritonitis can result. The infarcted intestinal loop may be resorbed, leaving an area or areas of intestinal atresia. Infants with meconium ileus are also at increased risk of developing cholestasis.
After birth, unlike normal neonates, infants with meconium ileus fail to pass meconium in the first 12 to 24 hours. They have signs of intestinal obstruction, including emesis that may be bilious and abdominal distention. Loops of distended small bowel sometimes can be palpated through the abdominal wall and may feel characteristically doughy. Meconium peritonitis with respiratory distress and ascites can occur secondary to perforation.
Prenatal ultrasonography can detect changes in utero suggestive of cystic fibrosis and meconium ileus (eg, dilated bowel, polyhydramnios), but these changes are not specific.
Diagnosis of meconium ileus is suspected in a neonate with signs of intestinal obstruction, particularly if a family history of cystic fibrosis exists. Patients should undergo abdominal x-rays, which show dilated intestinal loops; however, fluid levels may be absent. A “soap bubble” or “ground glass” appearance due to small air bubbles mixed with the meconium is diagnostic of meconium ileus. If meconium peritonitis is present, calcified meconium flecks may line the peritoneal surfaces and even the scrotum. A water-soluble contrast enema reveals a microcolon with an obstruction in the terminal ileum.
Patients diagnosed with meconium ileus should be tested for cystic fibrosis.
Obstruction may be relieved in uncomplicated cases (ie, without perforation, volvulus, or atresia) by giving ≥ 1 enema with a dilute radiographic contrast medium plus N-acetylcysteine under fluoroscopy; hypertonic contrast material may cause large gastrointestinal water losses requiring IV rehydration.
If the enema does not relieve the obstruction, laparotomy is required. A double-barreled ileostomy with repeated N-acetylcysteine lavage of the proximal and distal loops is usually required to liquefy and remove the abnormal meconium.