Meconium, a dark green substance, is a newborn's first stool. Newborns expel meconium almost always in the first 24 hours of life. If the meconium is abnormally thick or tarlike, it can block the last part of the small intestine, called the ileum. This blockage is referred to as meconium ileus. Above the blockage, the small intestine is enlarged (dilated), resulting in abdominal swelling (distention). Below the blockage, the large intestine (colon) is narrow (called microcolon) because nothing is passing through it.
Meconium ileus is most often an early sign of cystic fibrosis. Cystic fibrosis causes intestinal secretions to be abnormally thick and sticky, and the secretions stick to the lining of the intestine, causing an obstruction of the small intestine. These extremely sticky secretions are the first indication of illness in 10 to 20% of children with cystic fibrosis. Newborns with meconium ileus almost always develop other symptoms of cystic fibrosis later. Meconium plug syndrome is similar to meconium ileus except that it is the large intestine that is blocked by meconium.
Meconium ileus is sometimes complicated by
The small intestine can perforate because it is very distended or because the dilated small intestine has twisted on itself (volvulus), which blocks the intestine's blood supply. Perforation is a dangerous condition causing leakage of meconium into the abdominal cavity. If perforation occurs before birth, the affected part of the small intestine may be shrunken and narrow (intestinal atresia), which may require surgery after birth. If perforation occurs after birth, leakage of meconium causes inflammation and infection (peritonitis), which can lead to shock and death.
After birth, newborns usually pass meconium in the first 12 to 24 hours. However, newborns with meconium ileus do not pass meconium within this time frame and also have symptoms of intestinal blockage, including vomiting and abdominal swelling. Doctors may feel enlarged loops of small bowel through the abdominal wall.
If doctors do a prenatal ultrasound, they sometimes can see signs that the fetus's intestine is blocked.
However, doctors usually first suspect the diagnosis after birth, when the newborn has symptoms of intestinal blockage. Doctors strongly suspect meconium ileus if the newborn has a family history of cystic fibrosis or if routine newborn screening tests are positive for cystic fibrosis. If doctors suspect meconium ileus, they do abdominal x-rays, which show enlarged loops of the small intestine. Sometimes they also take x-rays after giving an enema using a liquid substance that is visible on x-rays (radiopaque contrast agent). The enema shows that the colon is narrower than normal (called a microcolon) and that there is a blockage near the end of the small intestine.
Newborns that are diagnosed with meconium ileus are tested for cystic fibrosis.
Infants who have a perforated or twisted intestine need immediate surgery.
If there is no perforation or twisting, doctors try to wash out the meconium blockage using an enema. The enema contains N-acetylcysteine, which breaks down and softens the thick meconium to allow it to pass through the intestine and out the rectum. If the enema does not remove the blockage, doctors do surgery to cut open the intestine and remove the meconium. Usually they bring the open ends of the intestine out through the wall of the abdomen (ileostomy). They do more enemas through the open ends of the intestine until the meconium is completely removed. Later, the doctors do another operation to put the ends of the intestine back together.
After the blockage is removed and stool begins passing through the area, the narrowed colon eventually widens out to its normal diameter.
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