Acute
intestinal obstruction of the newborn
Neonatal intestinal obstruction has an
approximate incidence of 1:2000 live births. Congenital atresia and stenosis are
the commonest causes. Volvulus neonatorum, meconium ileus and Hirschsprung's disease may also be responsible.
Congenital
atresia
The incidence of atresia varies with
anatomical site:
•
duodenum — 35 per cent;
•
jejunum — 15 per cent;
•
ileum — 25 per cent;
•
ascending colon — 10 per cent;
•
multiple sites — 15 per cent.
The
high incidence of multiple sites makes peroperative assessment of the whole
small and large bowel mandatory. Except in the case of duodenal atresia there
are frequently associated abnormalities of the heart and great vessels.
Atresia/stenosis
of the duodenum
Atresia and stenosis occur with equal
frequency. In most cases, except for the oesophagus, duodenum and rectum, the
atresia is a result of an intrauterine vascular accident occurring late in
pregnancy such as volvulus, intussusception or strangulation at the umbilical
ring. As the foetus is germ-free the ischaemic portion is absorbed and
disappears. In the presence of complete obstruction, persistent vomiting occurs
from birth. The presence or absence of bile is dependent on the relationship of
the septum to the duodenal papilla. Bile-stained vomiting is nearly always
organic in origin. Distension is often absent but visible peristalsis may be
seen in the left upper quadrant. Atresia of the duodenum occurs at the level of
the ampulla of Vater. Thirty per cent of babies have associated Down’s
syndrome. Radiography reveals a classic so-called double stomach due to gross
distention of the stomach and upper part of the duodenum with two air—fluid
levels (Fig. 58.21).In
cases of partial obstruction the location of the lesion may be confirmed by
installation, via a nasogastric tube, of a small volume of gastrograffin. Once
the lesion is confirmed the medium must be aspirated. Suprapapillary duodenal
atresia may be distinguished from oesophageal atresia by the absence of
dribbling saliva, and from infantile pyloric stenosis by the absence of a lump.
Duodenal
obstruction in infancy may also be due to midgut volvulus, a band obstruction or
an annular pancreas.
Treatment
Surgery is required as soon as resuscitation
is complete. Duodenojejunostomy is the operation of choice. A silastic
catheter is introduced through a stab incision in the antrum and guided through
the anastomosis. A Witzel gastrostomy is constructed around the proximal tube
which is brought out through a stab incision. Early enteral feeding through this
tube is recommended.
Atresia/stenosis
of the jejunum/ileum
There are four main types:
•
type 1 — diaphragm with continuity of the bowel wall;
•
type 2 — gap between the two ends (may be connected by fibrous cord)
plus a mesenteric defect;
•
type 3 — multiple atresias;
•
type 4 — apple peel atresia with loss of dorsal mesentery.
The
vital importance of a diagnosis lies in the fact that proximal distention of the
bowel may be so great that the vascular integrity of the bowel wall is
compromised leading to gangrene and perforation (Fig.
In
ileal atresia the child is born with abdominal distension or it presents within
24 hours of birth. In jejunal atresia early distention is lacking but vomiting
occurs early. In both conditions the vomit contains bile and some meconium is
likely to be evacuated.
Radiography
Plain radiographs are only diagnostic when air—fluid levels are seen. When they are present the obstruction is usually well advanced.
Surgery
If the stenosis is ileal and the discrepancy
in bowel diameter above and below the obstruction is marked the two limbs may he
brought out in a manner similar to the Paul—Mikulicz procedure. The proximal
limb will need to he proud of the abdominal wall (usually by eversion) in order
to prevent skin excoriation. Secondary closure by circumstomal mobilization and
anastomosis, rather than use of crushing clamps, is recommended. When the
stenosis is jejunal, the impact of the high jejunostomy output can make
subsequent management difficult and wherever possible an end-to-end anastomosis
is recommended.
Arrested
rotation
Up to 10 weeks of gestation the gut lies
outside the abdominal cavity. The orderly return may he arrested at any stage
resulting in four major types of arrest.
The
whole bowel may remain free as a narrow-based mesentery. The caecum may he
displaced with transduodenal bands. The intestine may return in a clockwise
direction producing a reversed intestinal rotation or a failure of rotation
altogether, with the small bowel on the right and the large bowel on the left.
The
most common anomaly is where the caecum remains in the left hypochondrium and a
peritoneal band is found running from the caecum to the right side of the
abdomen and then across the second part of the duodenum — the transduodenal
hand of Ladd. The symptoms of repeated vomiting, due to pressure on the
duodenum, and the radiographic appearances are identical to those of duodenal
stenosis. Treatment consists of early laparotomy after appropriate
resuscitation. The band is divided near its attachment to the parietal
peritoneum. Often there is a second band which must also be divided, extending
from the midline to the commencement of the caecum. The caecum and the colon are
centred on the left of the abdominal cavity with the small bowel on the right
(Nixon).
Meconium ileus
This is the neonatal manifestation of cystic
fibrosis. Meconium is normally kept fluid by the action of pancreatic enzymes.
The terminal ileum becomes filled with meconium and viscid mucus resulting in
progressive inspissation in utero and
neonatal obstruction. Inspissated meconium may be palpated as a rubbery
swelling. Abdominal radiography may reveal a distended small intestine, with
mottling. Fluid levels are generally not seen. Unlike ileal atresia there is no
abrupt termination of the gas-filled intestine. As the condition is due to an
autosomal recessive genetic defect a family history may he present. Further
assessment includes absence of trypsin from stool or bile and a concentration of
sodium chloride in sweat greater than 80 mmol/litre, or a negative
immunoreactive blood trypsin estimation.
Forty
per cent of cases are associated with complications such as volvulus neonatorum,
atresia or meconium peritonitis (Dickson). Any evidence to suggest an acute
intra-abdominal process due to twisting of the grossly distended proximal bowel
indicates the need for urgent laparotomy. When this is not so, a gastrografin or
mypaque enema may be given to confirm the diagnosis. The radio-opaque fluid will
pass easily to the ileum where it may disperse the obstructing meconium and
relieve the condition owing to its high osmolarity and detergent action. As the
instilled solution is markedly hypertonic, the rapid loss of fluid into the
bowel lumen must be corrected by replacement. If conservative management fails,
laporotomy is indicated. The only condition with which meconium ileus may be confused is
Hirschsprung’s disease affecting the whole colon. The standard treatment is
resection of the most dilated segment with an end-to-side anastomosis of the
colon to the ileum. The distal ileal opening is formed into an ileostomy,
through which the meconium may he irrigated postoperatively (the Bishop—Koop
operation). The ilesotomy becomes a mucus flstula which usually requires
subsequent closure (Fig. 58.23).
Necrotising
enterocolitis
This is a common phenomenon amongst sick
premature neonates. The risk is inversely proportional to birth weight and may
be associated with hypoxia, hypothermia, hypotension and umbilical artery
cannulation. The ileum, caecum, distal colon and total colon are affected with a
complete spectrum from mucosal to transmural necrosis.
The
usual presentation is bilious vomiting, abdominal distension, colour change and
lethargy in a high-risk neonate. The abdomen is usually soft. Abdominal
radiographs may show pneumatosis intestinalis or free intraperitoneal air.
Management consists of aggressive resuscitation with intravenous feeding. The
optimal time for surgery is not in the acute phase as the baby can withstand the
pressure of necrosis better than an adult but not the stress of laparotomy. At
laparotomy excision of all necrotic bowel with primary anastomosis is usual. The
overall mortality is 25 per cent with 10—30 per cent of neonates developing a
colonic stricture.