Pradeep Nazarey and Thomas T. Sato
Meconium ileus describes the presence of neonatal intestinal obstruction secondary to the pathophysiologic changes in stool character from cystic fibrosis (CF). Approximately 10% to 20% of newborn infants with CF will present with meconium ileus. Detailed discussion of the pathophysiology and diagnosis of CF is found in Chapter 514.1
Newborn infants with meconium ileus present with symptoms and signs of neonatal intestinal obstruction secondary to abnormally thick, viscous meconium that creates mechanical intestinal obstruction. The infants will have abdominal distention, feeding intolerance with or without bilious emesis, and fail-lure to pass meconium. The meconium is high in protein content given the relative deficiency of pancreatic proteinases and is often described as sticky, tarlike, and tenacious. The infant may have meconium-filled intestinal loops with a distended, “doughy’ character on palpation.6 Initial passage of meconium or rectal examination may find white mucus or thick, grey meconium. The presence of neonatal peritonitis is more typical of intestinal perforation or volvulus, whereas infants with in utero intestinal perforation and pseudocyst formation may have a palpable abdominal mass without significant tenderness. Infants with meconium ileus will typically have intestinal obstruction of the terminal ileum from meconium concretions or pellets; a small, unused but functionally normal microcolon may be observed. The proximal intestine is often distended, with muscular hypertrophy of the intestinal wall.
Simple meconium ileus is characterized by mechanical obstruction of the intact intestinal lumen by abnormally thick meconium. In such cases mechanical removal of the meconium impaction, usually by retrograde irrigation or contrast enema, provides effective treatment. In contrast, fetal intestinal distention from meconium can lead to proximal volvulus of the dilated intestinal segment and perforation or atresia from loss of mesenteric vascular supply. These events are categorized together as complicated meconium ileus because their treatment typically requires operative intervention. Complicated meconium ileus associated with in utero intestinal perforation classically presents with neonatal intestinal obstruction and a calcified peritoneal pseudocyst from sterile meconium peritionitis.
Plain abdominal radiographs are the initial diagnostic test of choice in most neonates with suspected neonatal bowel obstruction. Infants with meconium ileus will have multiple fluid-filled loops of intestine. The mixture of thick meconium and gas together create a “soap-bubble” or “ground-glass” appearance of the intestine on abdominal radiographs. More proximal gas-filled intestinal loops may be observed. A calcified, cystic abdominal mass visible on plain radiograph is highly suspicious for complicated meconium ileus.
Retrograde contrast enema is useful from both a diagnostic and therapeutic standpoint. Infants with simple meconium ileus will have a patent, unused microcolon. Reflux of contrast into the distal ileum will often demonstrate the obstructing meconium. The inability to reflux contrast into the dilated proximal bowel is consistent with either persistent obstruction from meconium or intestinal atresia.
Neonates with suspected meconium ileus should be managed as any infant with suspected intestinal obstruction. The infant should not be fed, a nasogatric or orogastic tube should be placed, and intravenous fluid should be provided to establish euvolemia. The initial treatment of choice in simple meconium ileus is retrograde contrast enema with the goal of mobilizing the impacted meconium. Approximately 70% of newborns are successfully treated with retrograde irrigation using hyperosmolar contrast agents or dilute mucolytic agents such as N-acetylcysteine. Irrigation of the inspissated meconium is greatly aided by retrograde contrast guided by real-time fluoroscopy. Multiple irrigations using contrast or N-acetylcysteine may be required to adequately clear the meconium from the intestinal lumen. Intestinal perforation or mucosal injury from neonatal retrograde enema is rare at experienced neonatal and pediatric centers.
Indications for operative exploration include complicated meconium ileus with pseudocyst formation, volvulus, intestinal perforation, atresia, or persistent intestinal obstruction despite retrograde enemas. Simple meconium ileus with persistent intestinal obstruction despite retrograde irrigation is treated operatively by disimpacting the obstructing meconium and evacuating the remaining meconium from the intestinal tract. Usually, this requires opening the intestine, direct removal of the obstructing meconium, and irrigating the remaining meconium from the intestinal lumen. Primary closure of the intestine is preferred, although there are several historical operative techniques for diverting enterostomy in the setting of meconium ileus. Operative treatment of complicated meconium ileus with or without intestinal atresia must be individualized based upon the infant’s clinical condition and operative findings. Following return of gastrointestinal function and initiation of enteral feeding, oral pancreatic enzyme replacement is necessary.
MECONIUM PLUG SYNDROME
This clinical entity is characterized by neonatal intestinal obstruction secondary to a meconium plug. In contrast to the microcolon observed in meconium ileus, infants with meconium plug syndrome will usually have a normal rectum and colon. The infant will present with abdominal distention, and spontaneous meconium passage may not occur. Plain radiographs demonstrate dilated, gas-filled intestinal loops characteristic of distal bowel obstruction.
Retrograde contrast enema is diagnostic and, in most cases, therapeutic in delivering the meconium plug. Normal, bile-stained meconium is found proximal to the plug. Some infants with cystic fibrosis or Hirschsprung disease will present with intestinal obstruction from a meconium plug; therefore, infants with meconium plug syndrome should undergo newborn screening for cystic fibrosis and have rectal suction biopsy performed to exclude aganglionosis.
DISTAL INTESTINAL OBSTRUCTION SYNDROME
Distal intestinal obstruction syndrome or meconium ileus equivalent syndrome is intestinal obstruction from inspissated stool in children or adolescents with cystic fibrosis occuring outside of the neonatal period. Symptoms and signs of distal intestinal obstruction syndrome include feeding intolerance, bilious emesis, abdominal distention, and decreased or absent bowel movements. Plain abdominal radiographs are diagnostic of small bowel obstruction, with visible distal stool typically in the distal ileum and colon. Air-fluid levels are observed in upright plain films.
Treatment of distal intestinal obstruction syndrome includes retrograde contrast enema until the obstructing stool is solubilized and reflux into the proximal, dilated bowel is accomplished. Following hydrostatic disimpaction, either retrograde enemas or oral cathartic agents may be employed on a temporary basis until normal stooling patterns are established. Careful review of pancreatic enzyme dosage is warranted to ensure adequate replacement. It is important to remember that patients with cystic fibrosis and a history of neonatal meconium ileus requiring operation are also at risk for adhesive small bowel obstruction, and exploration is warranted if the obstruction is not readily resolvable via contrast enema.