Meconium ileus is the intestinal blockage which is due to cystic fibrosis. Approximately 15% to 20% of infants with CF present with intestinal obstruction related to meconium ileus. Although it originally was thought that CF primarily affected the pancreas, it now is known that it also affects the secretions from the intestine.
CF is the most common life-shortening inherited disease in North America. CF is a complex disorder of the lungs and digestive systems. The genetics of CF are well understood with families with the disease carrying a one in four chance of having another child with the disorder. The incidence of carriers of the gene in whites is approximately 1 in 20. People of European extraction have a 1 in 3200 incidence of having a child with CF, whereas the incidence decreases to 1 in 15,000 in African-Americans and is much less in Asians. Collins first identified the genetic mutations responsible for the disorder in 1989. Since this first genetic mutation was isolated, more than 800 gene abnormalities have been identified.
In the intestine, CF leads to thickening of the meconium (first stool with the intestine of the newborn) which causes a blockage of the last portion of the small intestine.
The diagnosis of CF may be made using a variety of tests. Because it is not possible to test for all of the hundreds of genetic mutations, many approaches are used. Newborns may be tested with a dried blood spot for immunoreactive trypsinogen. This test may be falsely positive which demands that additional testing be performed. Sweat chloride testing (positive if the sweat chloride level is >60 mEq/L) is accurate, and most patients should undergo this test. Only 1% to 4% of CF patients have a normal test, but the test depends on the ability to collect sufficient quantities of sweat (at least 100 mg of sweat must be obtained), which may be difficult in neonates. Genetic testing is used increasingly. Commercial tests typically examine DNA for 25 to 100 of the most common mutations (95% of all CF patients).
Pathophysiology of Meconium Ileus
Because the small intestinal mucus glands produce overly thick secretions even in utero, the meconium formed by these infants is abnormally sticky and adherent. Characteristically in meconium ileus, the proximal ileum is greatly enlarged and contains thick, sticky meconium, whereas the last part of the ileum and colon are collapsed and obstructed by thickly packed, round, mucus plugs that resemble rabbit pellets (Fig. 62-2).
FIGURE 62-2: Simple obturation obstruction by inspissated meconium pellets. B, Complicated meconium ileus in three forms: atresia, volvulus, and perforation.
Infants born with this form of the disease have so-called simple meconium ileus obstruction of the intestine. In utero, this may progress, however, to complicated meconium ileus. In such a process, the massively dilated (enlarged), upstream intestine twists and ruptures. If this occurs early in gestation, one or more atresias (intestinal blockages) may be produced. If a twist (volvulus) of the small intestine occurs late in gestation, infants may develop intestinal rupture when the meconium spills into the abdomen.
Intestinal obstruction in infants with meconium ileus is generally evident within 24 to 48 hours after birth. Although a family history of CF is helpful, it is present only in 20% of patients. In approximately 20% of patients, particularly patients with complicated meconium ileus, there is a history of maternal polyhydramnios (excess amniotic fluid in the uterus of the mother). Although meconium ileus is uncommon in premature infants, many of those with meconium ileus are small for gestational age.
With meconium ileus, three signs of intestinal obstruction are generally evident: (1) abdominal distention, (2) vomiting of bilious (green, yellow material), and (3) failure to pass meconium (first stool in the newborn) within 48 hours. At times, it is possible to feel an enlarged intestinal loop filled with meconium. With complicated meconium ileus, patients generally present either at or shortly after birth because of severe abdominal distention that often is associated with breathing problems because the abdomen pushes up on the lungs. At times, the abdominal wall is red and inflamed. In these cases the blood pressure may be unstable and these infants may appear extremely ill. In patients with simple obstruction, one may see varying-sized loops of distended intestine and a “soap bubble” appearance of portions of the abdomen, particularly the right lower area. Other disorders that may share some of these xray findings include Hirschsprung’s disease, ileal atresia, and meconium plug syndrome. (Figure 62-3)
FIGURE 62-3 Radiographs of infant with meconium ileus. A, Plain flat plate of abdomen. Note “soap bubble” appearance in right lower area of the abdomen (arrows). B, Contrast enema with microcolon (very small colon) and thick, obstructing meconium in the terminal ileum (arrows).
When meconium ileus is suspected, a contrast enema study should be performed. The classic finding is a small colon filled with pellet-like meconium when contrast material goes back into last part of the small intestine. The xray dye may be used to wash out the obstructing plugs and dried out meconium. In patients with complicated meconium ileus, a contrast enema study is not required before laparotomy because xrays are often diagnostic. After relief of intestinal obstruction, the diagnosis of CF should be verified.
Simple Meconium Ileus
The obstructing plugs in patients with meconium ileus may be washed out. With this method, soluble contrast material is used. Regardless of the contrast material used. Approximately 30% of patients with simple meconium ileus may be managed this way, but the success rate varies widely. The remainder of patients require operative management.
In simple meconium ileus, the goal of surgery is to evacuate completely the obstructing plugs and meconium from the small intestine. One method that may be used is to irrigate the intestine and colon clear of plugs of obstructing meconium by making an opening in the small intestine. The opening in the small intestine may then be closed or brought out as an ileostomy. Many surgeons use this approach today. At times, intestinal removal with re-attachment may be needed, provided that all of the plugs can be washed out of the small intestine and colon. An alternative method in patients in whom the small intestine cannot be washed out or whose condition is precarious is the formation of a temporary ileostomy of one of a variety of types. Some surgeons use a double-barreled ileostomy. The downstream ileostomy provides an opportunity for irrigation of obstructing plugs from the downstream intestine. Cumbersome, one can place a tube into the distal stoma.
Complicated Meconium Ileus
Complicated meconium ileus means that the infant has intestine that is blocked or ruptured. Under these circumstances, dead or blocked intestine should be removed, then it is generally best to perform a double- barreled
Postoperatively, careful attention must be given to blood fluid and electrolytes and management of pulmonary complications, such as infection. Patients also require careful nutritional management. Because the pancreas doesn’t work well, supplemental pancreatic enzymes and lipid-soluble vitamins are required. Because of varying degrees of protein, fat, and carbohydrate malabsorption, special formulas such as Pregestimil are generally best. Finally, patients with small bowel stomas may lose large amounts of zinc, magnesium, bicarbonate, and sodium. Failure to thrive occurs unless these patients receive sodium supplementation.
FIGURE 62-4: Operative options for surgical treatment of meconium ileus.
In addition to pulmonary infection, many patients may have malabsorption, and intestinal obstruction. In older children who do not comply with enzyme supplementation, a meconium ileus–like picture that has been termed meconium ileus equivalent may occur that affects approximately 10% of cystic fibrosis patients. The clinical picture is identical to that of simple meconium ileus in newborns, and enemas are usually sufficient for relief. Additional pancreatic enzyme supplementation then is provided. In the mid-1990s, the use of high concentrations of pancreatic enzymes (mean dose 19,000 U/kg/day) resulted in the development of narrowing of the colon in many CF patients that required resection so that appropriate caution is in order.
Results and Outlook
In more recent years, survival has improved, with current operative mortality being 10% to 20%. The long-term outlook is the same as for all patients with CF, in whom the average life expectancy is now in the range of 32 years (based on 1998 statistics). Lung transplantation has become a promising option for selected patients with end-stage pulmonary disease related to CF.
Article and graphics adapted from O'Neill: Principles of Pediatric Surgery. © 2003, Elsevier.