Description
Meconium plug syndrome, also referred to as functional immaturity of the colon or transient colonic hypoganglionosis, is a condition observed in newborns. It is characterised by the obstruction of the large intestine due to the accumulation of meconium. Meconium, the infant’s first stools, is a greenish-black, sticky substance that is usually passed in the first few days after birth.
Pathogenesis
The pathogenesis of meconium plug syndrome is not fully understood. One hypothesis suggests that it might be due to transient functional immaturity of the colon, resulting in delayed passage or inspissation of meconium. This may cause a partial or complete colonic obstruction. It should be noted that while the condition is referred to as “transient colonic hypoganglionosis”, the normal presence of ganglion cells has been documented in cases, so the terminology is likely a misnomer.
Epidemiology, Risk Factors & Associations
This condition is seen more often in full-term infants (85% of cases) than in preterm infants. The incidence is believed to be approximately 1 in 500 to 1 in 1000 live births. Risk factors include maternal diabetes, maternal use of magnesium sulphate for eclampsia, and Down’s syndrome. It is also seen more often in infants of mothers who have received medications affecting the bowel’s muscular activity, such as opioids.
Clinical Features
Typical features include a failure to pass meconium within the first 24 to 48 hours of life, abdominal distention, and vomiting. Occasionally, it can present with features of neonatal intestinal obstruction, including bilious vomiting and abdominal distension.
Complications
If untreated, complications of meconium plug syndrome may include bowel perforation and peritonitis. However, with appropriate treatment, most infants have a good outcome.
Pathological Features
The hallmark of meconium plug syndrome is the presence of a thick, sticky meconium plug obstructing the colon. Histologically, the colon appears normal in meconium plug syndrome, with an adequate number of ganglion cells, thereby differentiating it from Hirschsprung disease.
Radiological Features
General Features
- The obstruction typically occurs in the left colon, but it can extend to the entire colon.
- Dilated bowel loops – bowel diameter greater than the interpedicular width of L1
- Air-fluid levels may be seen on plain films (lateral decubitus).
- An associated “soap-bubble” or “ground-glass” appearance may be noted on abdominal radiography due to meconium mixing with air.
XR
- Dilated loops of bowel, with calibre greater than the interpedicular width of L1.
- May show multiple air-fluid levels.
- Absence of rectal gas 24 hours after birth
FL
- Enema is both diagnostic and therapeutic. Water-soluble contrast may induce meconium passage.
- Dilated left-sided colon with an intraluminal filling defect corresponding to the meconium plug.
- Filling defect may be long and cylindircal
- Rectum is normal in size
Differential Diagnosis
Other differentials of low obstruction:
Large Bowel
- Small Left Colon Syndrome (SLCS): Small left colon and meconium plug syndrome are overlapping entities in the total spectrum of functional intestinal obstruction in newborn infants. SLCS presents with similar symptoms to MPS including abdominal distension and a delay in passing meconium. Radiographically, a ‘transition zone’ can be seen at the splenic flexure with a small calibre distal colon and a normal or dilated proximal colon. It is often associated with maternal diabetes. Treatment typically involves supportive care until the passage of meconium, and then initiation of feeding.
- Hirschsprung’s Disease: This condition often presents with failure to pass meconium within the first 48 hours of life, which is also seen in MPS. However, HD is characterised by the absence of ganglion cells in the myenteric and submucosal plexus of the distal bowel. Radiographically, there is reversal of the rectosigmoid ratio, i.e. <1). A rectal biopsy is often necessary for diagnosis.
- Anorectal Malformations: These congenital anomalies can also present with failure to pass meconium and may have associated anomalies like fistulas. Physical examination can aid in diagnosis.
- Necrotising Enterocolitis (NEC): Typically seen in preterm infants, NEC presents with feeding intolerance, bloody stools, and abdominal distension. Radiological findings usually show pneumatosis intestinalis, portal venous gas or pneumoperitoneum.
- Colonic atresia: Rare congenital malformation where there may be one or more atretic colonic segments. Anal opening is present.
Small Bowel
- Necrotising Enterocolitis: Can also affect small bowel.
- Meconium Ileus: Meconium is abnormally thick or sticky causing obstruction of the small bowel, usually the terminal ileum. It is commonly associated with cystic fibrosis. It may be differentiated by a history of polyhydramnios, a palpable abdominal mass and on imaging, a ‘soap-bubble’ or ‘ground-glass’ appearance in the right lower quadrant.
Management
- The primary management of meconium plug syndrome is supportive as it usually resolves with time as the maturity of colonic musculature improves.
- The obstruction can otherwise be relieved by the administration of a contrast enema, which also helps confirm the diagnosis.
- Surgical intervention is rarely required and is reserved for complications such as bowel perforation.
- There is typically good prognosis.