++
Meconium ileus describes the presence of neonatal intestinal
obstruction secondary to the pathophysiologic changes in stool character
from cystic fibrosis (CF). Approximately 10% to 20% of
newborn infants with CF will present with meconium ileus. Detailed
discussion of the pathophysiology and diagnosis of CF is found in Chapter 514.1
+++
Clinical Presentation
++
Newborn infants with meconium ileus present with symptoms and signs
of neonatal intestinal obstruction secondary to abnormally thick,
viscous meconium that creates mechanical intestinal obstruction.
The infants will have abdominal distention, feeding intolerance
with or without bilious emesis, and faillure to pass meconium. The
meconium is high in protein content given the relative deficiency
of pancreatic proteinases and is often described as sticky, tarlike,
and tenacious. The infant may have meconium-filled intestinal loops
with a distended, “doughy’ character on palpation.6 Initial
passage of meconium or rectal examination may find white mucus or
thick, grey meconium. The presence of neonatal peritonitis is more
typical of intestinal perforation or volvulus, whereas infants with
in utero intestinal perforation and pseudocyst formation may have
a palpable abdominal mass without significant tenderness. Infants
with meconium ileus will typically have intestinal obstruction of
the terminal ileum from meconium concretions or pellets; a small,
unused but functionally normal microcolon may be observed. The proximal
intestine is often distended, with muscular hypertrophy of the intestinal
wall.
++
Simple meconium ileus is characterized by mechanical obstruction
of the intact intestinal lumen by abnormally thick meconium. In
such cases mechanical removal of the meconium impaction, usually
by retrograde irrigation or contrast enema, provides effective treatment. In
contrast, fetal intestinal distention from meconium can lead to
proximal volvulus of the dilated intestinal segment and perforation
or atresia from loss of mesenteric vascular supply. These events
are categorized together as complicated meconium ileus because their treatment
typically requires operative intervention. Complicated meconium
ileus associated with in utero intestinal perforation classically presents
with neonatal intestinal obstruction and a calcified peritoneal
pseudocyst from sterile meconium peritionitis.
++
Plain abdominal radiographs are the initial diagnostic test of
choice in most neonates with suspected neonatal bowel obstruction.
Infants with meconium ileus will have multiple fluid-filled loops
of intestine. The mixture of thick meconium and gas together create
a “soap-bubble” or “ground-glass” appearance
of the intestine on abdominal radiographs. More proximal gas-filled
intestinal loops may be observed. A calcified, cystic abdominal
mass visible on plain radiograph is highly suspicious for complicated
meconium ileus.
++
Retrograde contrast enema is useful from both a diagnostic and
therapeutic standpoint. Infants with simple meconium ileus will
have a patent, unused microcolon. Reflux of contrast into the distal
ileum will often demonstrate the obstructing meconium. The inability
to reflux contrast into the dilated proximal bowel is consistent
with either persistent obstruction from meconium or intestinal atresia.
++
Neonates with suspected meconium ileus should be managed as any ...