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Meconium ileus is obstruction of the terminal ileum by abnormally tenacious meconium; it almost universally 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 almost always an early manifestation of cystic fibrosis, which causes GI secretions to be extremely viscid and adherent to the intestinal mucosa. These secretions are the presenting 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) and may be diagnosed by prenatal ultrasonographt. 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, 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.
Symptoms and Signs
After birth, infants fail to pass meconium in the first 12 to 24 h, which is typical for normal neonates. 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.
Diagnosis
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 (CF)).
Treatment
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.
Meconium Plug Syndrome
(Small Left Colon Syndrome)
Meconium plug syndrome is colonic obstruction caused by thick meconium.
Meconium plug syndrome usually occurs in infants who are otherwise healthy, but it is more common among infants of diabetic mothers and toxemic mothers treated with Mg sulfate. It is generally regarded as a functional immaturity of the colon, resulting in failure to pass the first stool.
Symptoms and Signs
Infants present in the first few days of life with failure to pass stools, abdominal distention, and vomiting. Thick, inspissated, rubbery meconium forms a cast of the colon, resulting in complete obstruction.
Diagnosis
Diagnosis is of exclusion and should be differentiated primarily from Hirschsprung's disease (see Congenital Gastrointestinal Anomalies: Hirschsprung's Disease).
Plain abdominal x-rays are nonspecific and can show signs of low intestinal obstruction. Conversely, contrast enema shows the characteristic appearance of the outline of the inspissated meconium against the wall of the colon, providing a double-contrast impression. Unlike meconium ileus, microcolon is not typically seen on x-ray with meconium plug syndrome.
Treatment
The water-soluble contrast enema can be therapeutic by separating the plug from the intestinal wall and expelling it. Occasionally, repeated enemas are required. Rarely, surgical decompression is required. Although most infants are healthy thereafter, diagnostic studies may be needed to rule out Hirschsprung's disease (see Congenital Gastrointestinal Anomalies: Hirschsprung's Disease) or cystic fibrosis (see Cystic Fibrosis (CF): Diagnosis).
Last full review/revision November 2007 by William J. Cochran, MD
Content last modified November 2007
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