Meconium Plug Syndrome

Meconium plug syndrome is functional lower intestinal obstruction in a term or near term infant caused by a plug of thick, inspissated meconium in the colon or rectum, with failure to pass meconium in the first 24 to 48 hours.

It is uncommon. Most infants recover after passage of the plug. A minority have underlying Hirschsprung disease or cystic fibrosis, so both must be excluded.

Associations include maternal magnesium sulphate treatment, maternal diabetes, maternal hypothyroidism, maternal opioid use, prematurity, small left colon syndrome, Hirschsprung disease, cystic fibrosis and neonatal hypothyroidism.

Pathophysiology.

Reduced colonic motility and dehydrated, viscous meconium cause a luminal plug that blocks the distal colon. The plug can itself be diagnostic and therapeutic once removed.

In cystic fibrosis, abnormal pancreatic and intestinal secretions increase meconium viscosity. In Hirschsprung disease, aganglionic distal bowel fails to relax.

• Progressive abdominal distension and bilious vomiting.
• No meconium passed in 24 to 48 hours, with a normally placed anus.
• Rectal examination may trigger explosive passage of a plug and stool.

Red flags.

• Tense distension with shock or fever suggests perforation or enterocolitis from underlying Hirschsprung disease.
• Delayed passage past 48 hours with persisting symptoms after plug passage.

• Abdominal X-ray: multiple dilated loops with air fluid levels suggest low obstruction.
• Water soluble contrast enema is diagnostic and often therapeutic. Findings are a filling defect (the plug) with a normal calibre colon.
• Exclude associated disease: suction rectal biopsy at least 2 cm proximal to the dentate line if symptoms recur or constipation persists, sweat chloride (over 60 mmol/L is diagnostic, 30 to 59 mmol/L is intermediate) or genetic testing for cystic fibrosis once the infant is 2 weeks old and over 2 kg, thyroid function tests and the newborn screening result for immunoreactive trypsinogen.

Differential diagnosis. Hirschsprung disease, ileal atresia, meconium ileus, anorectal malformation, small left colon syndrome, hypothyroidism and sepsis with ileus.

• Nil by mouth with nasogastric decompression and IV maintenance fluids of 60 to 80 mL/kg on day 1, increased by 10 to 20 mL/kg/day as required.
• Rectal stimulation with a lubricated thermometer or catheter, and a glycerol infant suppository.
• Warm 0.9% sodium chloride rectal washout, 10 mL/kg with a soft catheter, repeated as needed.
• Contrast enema using isotonic or diluted low osmolar contrast under fluoroscopy. Undiluted hyperosmolar agents risk fluid shifts and perforation.
• Antibiotics only for suspected sepsis or enterocolitis.
• Restart feeds once stool passes, abdomen is soft and aspirates are clear. Observe for 24 to 48 hours for recurrence.

Monitoring. Abdominal girth, stool passage, aspirates and electrolytes. Review at follow up for constipation or growth faltering.

Referral and escalation. Refer to paediatric surgery if the plug cannot be passed, perforation is suspected, or symptoms recur. Refer for cystic fibrosis and Hirschsprung disease workup when the findings suggest either.