Meconium ileus (also know as distal intestinal obstructive syndrome (DIOS)) is defined as an intestinal obstruction due to inspissated meconium within terminal ileum. It comes from the abnormal composition of the fetal meconium in cystic fibrosis. The most common cause of intestinal blockage without prior surgery in Caucasian children is DIOS. DIOS is described as protein rich, inspissated meconium causing obstruction of the distal ileum, and extremely viscid. DIOS may even be an early indication of a much more severe phenotype of Cystic Fibrosis.
Abnormalities of exocrine mucous secretion caused the meconium in DIOS differs from normal meconium with less water, lower level of sucrase, lower level of lactase, decrease of pancreatic enzymes, and increased albumin. All of the above causes a more viscous intestinal mucous making the meconium thick and dehydrated, obstructing the intestine.
Pediatric surgeons often evaluate newborns for suspected bowel obstruction, and in such cases DIOS should be considered in the differential diagnosis. Sonographic characteristics of DIOS are hyperbolic, intra-abdominal mass of inspissated meconium, non-visualization of the gallbladder, and dilated bowel.
Simple Meconium Ileus: newborns with uncomplicated DIOS appear healthy immediately after birth. Since DIOS is much like many types of neonatal small bowl obstruction, the clinician should consider and evaluate for malrotation, volvulus, meconium plug syndrome, small left colon syndrome, duodenal atresia, small bowel atresia, colonic atresia, Hirshsprung disease, anal stenosis, and rectal atresia. Failure to pass meconium (stool) may lead to bilious vomiting and abdominal distention.
Complicated Meconium Ileus
Half of all DIOS patients have complications, which may consist of volvulus, intestinal necrosis, intestinal atresia, meconium peritonitis, or bowel perforation. Complications can occur in utero (perforation or bowel compromise), immediately after birth or later after birth. Prenatal perforation may result in sign of peritonitis that don’t show up until after bacterial colonization. Abdominal distension can be severe enough to respiratory distress.
A pseudocyst formation caused by bowel perforation, is suggested by a palpable mass in the newborn. The neonate is often in extremis and needs immediate resuscitation and surgical exploration. Volvulus (twisted bowel) used to be the most common complication of DIOS. It can lead to loss of mesenteric blood flow which will lead to segmental necrosis and intestinal atresia associated with mesenteric defect. Some authors describe 4 types of meconium peritonitis:
Adhesive meconium peritonitis
Giant cystic meconium peritonitis
Infected meconium peritonitis
Bowel perforation is a common etiology in all four of the peritonitis forms.
Most DIOS patients can be treated nonoperatively with water-soluble enemas or. Textbook criteria for the enema cleanout is as follows:
1. The infant shows signs of no complications.
2. An initial diagnostic contrast enema must exclude other causes of neonatal distal intestinal obstruction.
3. The infant should be well prepared for enema.
4. The enema has to be done under fluoroscopic control.
5. Intraveneous antibiotics should be administered.
6. Close surgical supervision from initial evaluation throughout hospital course.
For complicated DIOS (see above), an operative approach is generally required.
In highly selected cases at tertiary care hospitals, Golytely via nasogastric tube at a low rate with close monitoring may be offered in consultation with pediatric gastrointestinal or pediatric surgical specialists.
T-tube ileostomy involes placing a surgical T-tube in the bowel to allow for further washouts. Other surgical options include a distal chimney enterostomy, also known as a Bishop-Koop. This procedure involves resection of the segment of ileum containing the mass of meconium. The distal ileum is brought out as an irrigating and decompressive ileosotomy. Nestled between the side of the distal segment of bowel just within the abdominal cavity and end of the proximal segment an anastomosis is created. This procedure allows normal gastrointestinal transit while managing distal obstruction through ileostomy, if needed. The advantage to using this method, in the absence of a distal obstruction, is that the stoma output isn’t difficult to manage. Successful resection of the anastomosis depends on the resection of compromised bowel, complete proximal distal evacuation of meconium, and the preservation of adequate blood supply of the anastomosis. Mikulicz double barrel enterostomy is also described, and preferred by some centers.
In surgical treatment, intraoperative instillation of Gastrophin may facilitate the evacuation of inspissated meconium. Tenacious meconium has to often be removed directly through enteronomy.