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Meconium ileus is obstruction of the terminal ileum by abnormally tenacious meconium; it most often occurs in neonates with cystic fibrosis. Meconium ileus accounts for up to 33% of neonatal small-bowel obstructions. Symptoms include emesis that may be bilious, abdominal distention, and failure to pass meconium. Diagnosis is based on clinical presentation and x-rays. Treatment is enemas with dilute contrast under fluoroscopy and surgery if enemas fail.
Meconium ileus is most often an early manifestation of cystic fibrosis (see Cystic Fibrosis), which causes GI secretions to be extremely viscid and adherent to the intestinal mucosa. These secretions are the presenting clinical manifestation of cystic fibrosis in 10 to 25% of cases.
Obstruction occurs at the level of the terminal ileum (unlike the colonic obstruction caused by meconium plug syndrome—see 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.
About 50% of cases are complicated by malrotation (see Malrotation of the Bowel), 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.
After birth, unlike normal neonates, infants with meconium ileus fail to pass meconium in the first 12 to 24 h. They have signs of intestinal obstruction, including bilious emesis 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, but these changes are not specific. Diagnosis 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 are often 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 barium enema reveals a microcolon with an obstruction in the terminal ileum.
Patients diagnosed with meconium ileus should be tested for cystic fibrosis (see Cystic Fibrosis : Diagnosis).
Obstruction may be relieved in uncomplicated cases (eg, 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 GI 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.
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