Meconium ileus

Meconium found in the intestine of a newborn, consisting of succus entericus (bile salts, bile acids, and debris from the intestinal mucosa) Meconium is normally evacuated within 6 hours of birth or earlier. Meconium ileus occurs with meconium becomes inspissated and obstructs the distal ileum. It is usually a manifestation of cystic fibrosis. It is usually understood as synonymous with cystic fibrosis until proven otherwise. Approximately 20% of infants with cystic fibrosis present with meconium ileus at birth. It may also be seen with pancreatic atresia or stenosis of the pancreatic duct. It may rarely occur without cystic fibrosis or pancreatic abnormality in cases likely related to gut immaturity (more favorable outcome). Further complications include ileal atresia or stenosis, ileal perforation, meconium peritonitis, and volvulus with or without pseudocyst formation. It is more common in white populations. It affects both sexes almost equally.

• Prenatal ultrasound findings associated with meconium ileus include polyhydramnios, fetal ascites, peritoneal wall calcifications, and intraabdominal cysts.
• Meconium is normally invisible radiographically.
• Occassionally, has a mottled appearance on radiographs during the first 2 days of life.
• Classically, a paucity or absence of air-fluid levels and a “bubbly” appearance of distended intestinal loops on radiographs.
• Microcolon seen on barium enema.
• Characteristic findings often not seen, and thus relatively unreliable.

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Meconium ileus must be differentiated from other diseases that cause a failure to pass meconium or abdominal distension in infants, including meconium plug syndrome, small left colon syndrome, and congenital hypothyroidism.

Disease	Prominent clinical features	Radiological findings
Meconium plug syndrome	Transient intestinal obstruction for 1-2 days after birth. Obstruction is functional due to dilated colon and delayed passage of feces. Usually seen in premature infants.[1]
Small left colon syndrome	Reduced caliber of the colon starting from splenic flexure and going down, causing intestinal obstruction. Characterized by a sudden change of the colon diameter. Usually associated with gestational diabetes.[2]
Distal small intestine/colon atresia	Failure to pass meconium due to failure of intestine recanalization. Proximal lesions have an earlier onset of symptoms than distal lesions. Colonic atresia may affect normal children or may be associated with other abnormalities as Hirschsprung’s disease or gastroschisis.[3]
Meconium ileus	Intestinal obstruction due to inspissation of meconium in the distal ileum. Most cases of meconium ileus are secondary to cystic fibrosis. Typically presents with failure to pass meconium and abdominal distension with or without vomiting. Meconium ileus may first present with complications, including perforation and volvulus.[4]
Congenital hypothyroidism	Most infants are born asymptomatic.[5] Symptoms, if present, may include, but not limited to: Macroglossia Hoarse cry Umbilical hernia Puffy facies Increased head circumference Hypothermia

• Meconium
• Meconium plug syndrome

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