60 Microcolon/Meconium Ileus

Clinical Presentation

Term neonate presents with a distended abdomen and failure to pass meconium after 48 hours.

Figure 60A

Radiologic Findings

Non-ionic contrast enema (Fig. 60A1) in a 2-day-old girl demonstrates a microcolon. Reflux of contrast has occurred into mildly dilated loops of distal ileum, containing meconium plugs, but does not reach the more proximal dilated air-filled loops. Further reflux was achieved during a repeat examination the following day (Fig. 60A2), with opacification of significantly more dilated loops in the mid-ileum, containing further inspissated meconium.

Diagnosis

Meconium ileus

Differential Diagnosis

Low gastrointestinal (GI) obstruction on abdominal radiograph-wide differential
- Ileal atresia
- Hirschsprung’s disease
- Functional immaturity/left colon syndrome
- Anorectal anomaly
- Colonic atresia
- Sepsis/electrolyte disturbance
- Megacystis-microcolon-hypoperistalsis syndrome (rare)
Microcolon on enema
- Ileal atresia—microcolon with reflux of contrast into nondilated distal ileum. If contrast reaches the atretic segment, an abrupt convex termination is seen, with residual unopacified dilated proximal small bowel loops.
- Megacystis-microcolon-hypoperistalsis syndrome (rare)—transient neonatal microcolon in association with a large-volume bladder and a variable degree of upper renal tract dilatation. Malrotation is common.
- Total colonic Hirschsprung’s disease (may present as a small-caliber colon, although not usually as small as a “microcolon”)

Discussion

Background

Meconium ileus is a neonatal obstruction of the ileum by abnormally viscid, inspissated pellets of meconium.

Etiology

Almost all cases are associated with an underlying diagnosis of cystic fibrosis (CF). Conversely, meconium ileus is the initial presentation of 10 to 15% of CF cases.
Rare cases have been described in association with partial pancreatic aplasia or stenosis of the pancreatic ducts.

Clinical Findings

Low GI obstruction—abdominal distension, failure to pass meconium, and sometimes vomiting — within the first 48 hours of life

Associated Conditions

Complications

Prenatal complications occur in —50% and include perforation, which may result in meconium peritonitis and/or pseudocyst formation (walled-off local perforation), intestinal atresia, and closed-loop segmental volvulus. Migration of intraperitoneal meconium through the patent processus vaginalis testis can result in multiple small calcified scrotal masses. Rare labial meconium masses are described in girls.
Postnatal perforation resulting in pneumoperitoneum
Iatrogenic perforation during diagnostic or therapeutic contrast enema

Figure 60B Supine (1) and cross-table lateral (2) abdominal x-ray of a 2-day-old girl showing generalized bowel dilatation with a mottled appearance of air mixed with meconium, in this case more prominent in the left flank. Enema confirmed meconium ileus with an underlying diagnosis of CF.