Meconium Ileus

General Considerations

• Obstruction of the small bowel in the terminal ileus from impacted meconium
• May develop in utero and manifests within 48 hours of birth

• Meconium is normally evacuated within first 6 hours
• Earliest sign of cystic fibrosis
• Autosomal recessive
• Predominantly Caucasians
• Diseased exocrine gland function affecting primarily the lungs and the pancreas
• May also be seen with other pancreatic disease such as stenosis of the pancreatic duct
• In a few cases, the pancreas is normal and there is decreased intestinal motility

Clinical Findings

• Abdominal distension
• Failure to pass meconium within 48 hours
• Bilious vomiting

Imaging Findings

• On conventional radiographs
• Meconium, being fluid density, is normally invisible on radiographs
• In meconium ileus, there may be dilated loops of bowel (small bowel) typically without air-fluid levels because of the viscosity of the secretions
• Bowel distension can achieve very large sizes
• Bubbly appearance of intestinal contents in the right lower quadrant
• On contrast enema
• Required to establish the diagnosis
• Nonionic contrast agents (e.g. Omnipaque or Hypaque) or dilute Gastrografin
• Fluid shifts have been reported with Gastrografin
• Microcolon
• Underused colon in antenatal obstruction
• May be seen with other causes of distal small bowel obstruction
• Multiple oval filling defects in distal ileum and colon from inspissated meconium
• On ultrasound
• Enlarged loops of bowel
• Possible RLQ “mass” representing inspissated meconium

Differential Diagnosis

• Hirschsprung’s disease
• Small bowel atresia with meconium ileus
• Meconium plug syndrome
• Functional immaturity of the ganglion cells in the colon leading to failure to pass meconium
• Considered same as small left colon syndrome
• Imperforate anus

Treatment

• Water soluble contrast enema usually clears the meconium

Complications

• Associated with cystic fibrosis in almost 100% of cases
• About 20% of patients with cystic fibrosis first present with meconium ileus
• Volvulus
• Ischemic bowel
• Bowel necrosis
• Ileal stenosis
• Ileal atresia
• Perforation

• Meconium peritonitis
• Usually produced by intrauterine bowel perforation
• Frequently the result of meconium ileus
• May be sterile at first but become infected

• Meconium ileus-equivalent syndrome is a term applied to a partial small bowel obstruction in an older patient with known cystic fibrosis

• While the bowel gas pattern may resemble that of meconium ileus, the findings are not due to meconium which is present only in the newborn

Meconium ileus. At top, a conventional radiograph of a newborn abdomen shows a "mass" in the right lower quadrant (white arrow) made up of loops of ileum with inspissated meconium, markedly dilated loops of bowel (black arrow) and a "soap-bubbly appearance to the meconium (white oval). In the contrast enema on the bottom, a small, unused microcolon (white arrows) is seen and there are filling defects representing meconium pellets in the terminal ileum and colon (black arrow).
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Meconium Ileus eMedicine  Hekmatnia, A; McHugh, K; Hiorns, M.