Meconium plug syndrome is a transient functional abnormality of the newborn's digestive system which consists of the delayed passage of the meconium (beyond 24-48 hours), abdominal distension, vomiting, and dilatation of the left colon. The disease is diagnosed and treated by radiographic contrast enema, but Hirschsprung disease and cystic fibrosis should be excluded.
Meconium plug syndrome, much like Hirschsprung disease, intestinal and anal atresia, anal stenosis, and intestinal malrotation, presents with progressive abdominal distension, an absence of meconium elimination, and bilious vomiting [1]. In this disease, the probable causes are intestinal hypomotility and increased consistency of fecal matter that adheres to the colonic wall and becomes immobile [2]. Abdominal inspection and palpation reveal dilated bowel loops.
The clinician should also evaluate the presence of predisposing factors of this disease, such as prematurity [3], cystic fibrosis [4], hypermagnesemia, Hirschsprung disease [5], hypotonia, hypothyroidism, and maternal diabetes. Provided that these factors are excluded, the long-term prognosis is excellent.
The physician should order plain abdominal radiographs in supine and left lateral decubitus positions, that point out the presence of dilated intestinal loops and an absence of rectal gas. Fluid levels are also absent throughout the small and large bowel. Diagnostic protocol implies that contrast enema is administered afterward. Barium and other contrast agents have been used, but some have been hyperosmolar and caused dehydration [6]. Furthermore, some detergents and wetting additives are toxic and should not be used [7], so clinical judgment is required to determine which contrast agent is most appropriate for the patient. This method reveals a dilated area of the colon and the meconium plug, causing total or partial obstruction and presenting a double-contrast effect [8]. Ribbon-like or sausage shaped filling defects are due to the presence of meconium. The rectum has normal size if Hirschsprung disease is absent. In some cases, the left colon may be constitutionally small, so the investigation will highlight a difference between colon diameters before and after the splenic flexure. Normally, an intestinal loop should not be wider than a lumbar vertebral body. The contrast enema can be performed more than once [9]. If the problem persists after one or two enemas, that should also have a therapeutic effect and lead to prompt meconium elimination, another cause like Hirschsprung disease should be evaluated by rectal-suction biopsy. Hirschsprung disease can be mimicked on radiological films in meconium plug syndrome because the descending colon distal to the plug may be collapsed, therefore a biopsy is highly recommended in this case. Radiological evaluation can also exclude meconium ileus, in which case the appearance is that of a microcolon, but is unable to differentiate between a large bowel and small bowel obstruction (duodenal or jejunoileal atresia, malrotation, volvulus). Differential diagnosis may also be aided by anorectal manometry.