Meconium Plug Syndrome

Etiology

The exact etiology of meconium plug syndrome is ill-defined. In a majority of cases, meconium plug syndrome occurs in isolation. There may be an association, however, with the following conditions: 

• Prematurity
• Neonates of mothers with diabetes - (gestational diabetes mellitus and chronic diabetes mellitus)
• Neonates of mothers  who received magnesium sulfate as a treatment for eclampsia or preterm labor

Moreover, according to a recent study, by Cuenca et al., an association with magnesium tocolysis was noted in 16% of the cases and only 3.2 % with Hirschsprung disease.[6] There is also significant clinical overlap with small left colon syndrome.[6][5] While the historical association of meconium plug syndrome and Hirschsprung disease has been unclear in some recent studies, other studies demonstrate that meconium plug syndrome (MPS) has an association with Hirschsprung disease (HSCR) in 13 to 38% of patients.[7][6][7][4]

Epidemiology

Meconium plug syndrome is not associated with sex. However, a higher incidence is seen in premature infants, infants of diabetic mothers, and mothers who receive tocolytic drugs. Furthermore, historically, meconium plug syndrome is associated with Hirschsprung disease and cystic fibrosis.[8] There is also a greater incidence in infants with a higher probability of cerebral insult.[9] There have been no reports of increased prevalence in a specific race, ethnic group, or geographical population.

Pathophysiology

The exact pathogenesis is unknown. The most commonly accepted hypothesis is that meconium plug syndrome is a transient functional colonic immaturity specifically of the myenteric nervous system. Consequently, peristalsis is ineffectual, and therefore the meconium remains in the colon for a more extended period, leading to higher water absorption and the development of meconium plugs that cause obstruction.

In diabetic mothers, the higher occurrence of neonatal hypoglycemia induces the pancreas to secrete glucagon. In turn, glucagon decreases peristalsis in the left colon. Furthermore, neonatal hypoglycemia stimulates the autonomic nervous system. Increased stimulation of the sympathetic nervous system causes a decrease in intestinal movement, which accelerates the development of meconium plugs.

History and Physical

The defining presentation of meconium plug syndrome is the inability to pass meconium within the first 24 to 48 hours of life. Subsequently, infants develop abdominal distension and vomiting. The vomiting can present with bilious emesis. Neonates often exhibit with a softly distended abdomen, occasionally with palpable intestinal loops.[5] Nasogastric aspiration yields bilious content—the clinical scenario that of distal intestinal obstruction.

Evaluation

Abdominal plain films are non-specific in the majority of cases. Crosstable or lateral imaging may demonstrate multiple air-fluid levels. However, plain abdominal films cannot distinguish with high specificity the difference between small and large bowel obstruction. Rarely, if there is any air in the rectum, may there be an outline of the meconium mas on an abdominal radiograph. The abdominal film may also demonstrate small bowel gas mixed with colonic meconium producing a granular appearance similar to necrotizing enterocolitis (NEC). When a granular pattern occurs within the first 12 hours, the diagnosis is most likely meconium plug syndrome, as NEC develops after >18 hours.[10] In contrast to meconium ileus, meconium plug syndrome radiographs do not demonstrate microcolon.

Contrast Enema is the investigation of choice and is often diagnostic and therapeutic.

The contrast enema, demonstrates the classical visualization of the meconium against the colonic wall, creating a double-contrast impression.[10][9] Water-soluble contrast is the agent of choice, as barium based contrast agents have a risk of causing peritonitis in case of perforation during the study.

Chloride sweat test - to rule out cystic fibrosis.[6]

Suction rectal biopsy- to rule out Hirschsprung disease, which is characterized by the absence of ganglion cells in the rectal biopsy specimen. In 13 to 38% of cases, meconium plug syndrome (MPS) has correlations with Hirschsprung disease (HD).[4] 

Serum electrolytes - To monitor the infant's electrolyte status during treatment with contrast enema agents.

Treatment / Management

Treatment is predominantly non-surgical. The primary motive is to stimulate the rectum or colon by using a water-soluble contrast enema. Some patients might require serial enemas, possibly using acetylcysteine.[9] Most of the cases respond immediately to the enema, with the instant passage of stools and cessation of abdominal distension.

If there is no passage of stools by 48 to 72 hours, surgical options may be a consideration. A suction rectal biopsy should be performed. Additionally, if temporary decompression of the bowel is necessary, a temporary ileostomy is performed. Additional surgical approaches include the Mikulicz double-barreled ileostomy, which has a zero risk of an intraabdominal anastomosis whereas the aesthetically pleasing option is a skin bridge temporary ileostomy.

More advanced options include a distal ileostomy with a Bishop-Koop anastomosis ( end to side ileal)- known as distal chimney enterostomy and a similar proximal chimney enterostomy called the Santulli procedure. Usually, ten days following the surgery, the enterostomies can be closed by performing an end-to-end anastomosis.[11]

Differential Diagnosis

Diagnosis of meconium plug syndrome (MPS) is a challenge because several other clinical entities present similarly. The differential diagnosis includes Hirschsprung disease, malrotation, meconium disease, and intestinal atresia. The major conditions that should be ruled out are listed below:

• Meconium ileus: Here, the inspissated meconium obstructs the small intestine rather than the colon and decreases the diameter of the colon, resulting in a microcolon.  In comparison, meconium ileus is a disease of critical nature as it has a higher rate of complications such as perforation, small bowel volvulus, peritonitis, and intestinal atresia and strong association with cystic fibrosis.[12]
• Small left colon syndrome(SLCS): Historically considered along with meconium plug syndrome as both are transient functional obstructions of the colon. SLCS characteristically presents a sudden change in the colonic diameter proximal to the splenic flexure. MPS occurs mostly in preterms, whereas SLCS occurs in full-term babies. A majority of both MPS and SLCS patients revert to normal spontaneously within 30 days.[13]
• Hirschsprung disease: the absence of ganglion cells can be differentiated on rectal biopsy.
• Anorectal malformations: diagnosed by physical exam.
• Malrotation: limited upper gastrointestinal contrast study to evaluate for malrotation. 
• Intestinal atresia: upper and lower gastrointestinal series

Prognosis

Meconium Plug Syndrome usually has an excellent prognosis. While a significant proportion of cases resolve spontaneously, almost all cases respond to water-soluble contrast enema, provided the absence of other underlying diseases. It is a relatively being condition that may resolve spontaneously or with contrast enema.

Meconium plug syndrome has links with diseases such as Hirschsprung diseases and cystic fibrosis. However, there is a wide range of reported incidence in the literature, and some of this may occur from institutional definitions and potential miscoding.[3]

Complications

Almost all cases resolve with conservative treatment and rare ones might need surgery. The surgical outcome is also excellent. However, rare complications include bowel perforation, necrosis of the bowel, meconium peritonitis.