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Neonatal Intestinal Obstruction 377
Figure 61.1: Radiograph showing ground-glass appearance of meconium ileus.
Figure 61.2: Meconium peritonitis with calcification and pseudocyst due to in
utero perforation.
Figure 61.3: Meconium ileus with perforation.
are present in the submucosal layer of the intestine and migrate from
the neural crest distally along the bowel to reach the rectum at about
7–10 weeks’ gestation. HD is the congenital absence of neuroganglion
cells; consequently, the peristaltic relaxation phase is absent distally,
and the affected intestine does not appropriately relax, causing a func-
tional obstruction. The extent of the aganglionic segment varies with
each patient, but extends from the distal rectum proximally. The level
at which the proximal but healthy bowel starts to dilate is called the
transition zone (Figure 61.5).
The genetic defects responsible for HD consist of abnormalities on
more than one chromosome and include the RET proto-oncogene, located
at chromosome 10q11.21. RET interacts with a protein termed EDNRB,
encoded by the gene EDNRB, which is located on chromosome 13.
Anorectal malformation
At 4 to 6 weeks’ gestation, the hindgut separates into the urogenital sinus
and the anorectum, which then undergoes canalisation. The distal third of
the anus develops from ectoderm and becomes the anal pit, whereas the
proximal portion of the anal canal is derived from mesoderm. An anal
membrane covers the canal until 8 weeks’ gestation, when it perforates
and becomes a patent anus. Imperforate anus results if this sequence of
events occurs improperly.
In summary, conditions of NIO include:
• hernia (inguinal, internal);
• atresia, stenosis, web (oesophageal, duodenal, jejunoileal, colonic);
• anorectal malformation;
• Hirschsprung’s disease;
• meconium ileus or plug; and
• malrotation with midgut volvulus.
Clinical Presentation
History
The history of NIO is typical for the level (high/ low) and type
(mechanical, functional) of obstruction. High intestinal obstruction
presents with early vomiting, whereas low intestinal obstruction pres-
ents with abdominal distention and later onset vomiting. Feeding intol-
erance with bile-stained vomiting, absent meconium, and abdominal
distention are therefore paradigmatic. With late presentation, the symp-
tom presentation might change due to complications and malnutrition.
On antenatal ultrasound, polyhydramnios is a common feature.
Intrauterine bowel dilatation may also be noted if scanned after 24
weeks’ gestation.
Physical Examination
Depending on the level of intestinal obstruction, the physical find-
ing is that of a distended abdomen. Within the African context, these
babies often present late with aspiration pneumonia, malnutrition,
and final events such as intestinal perforation and sepsis. A careful
examination and search for typical signs (e.g., abdominal distention,
peristaltic waves across the abdomen, absent anus or perianal fistulas,
severe distention, and malnutrition in HD) usually reveal the appro-
priate suspected diagnosis.
Investigations
The most important and useful test in any NIO is the abdominal
radiograph (AXR). A single supine and lateral shoot-through is usu-
ally sufficient. The distribution of the air contrast directs one to the
appropriate diagnosis. Very distended loops of bowel are indicative
of atresia. Long-standing drainage from a nasogastric tube (NGT),
however, could make such a diagnosis difficult. A duodenal atresia
could in this way be missed purely by the duodenal bulb being col-
lapsed from the ongoing drainage. A repeat radiograph with injection
of some air through the NGT facilitates the diagnosis.