Congenital Intestinal Obstruction:
Intestinal Atresia,
Malrotation of Colon,
Volvulus of Midgut
Intestinal
obstruction in newborn infants is caused by a variety of congenital anomalies,
and prompt diagnosis and treatment can be life-saving. The causes of such
intestinal obstructions may be atresia of the esophagus, diaphragmatic hernia,
annular pancreas, malrotation of the colon with volvulus of the midgut,
peritoneal bands mostly compressing the duodenum, internal or
mesentericoparietal herniations, meconium ileus, aganglionic megacolon,
imperforate anus, and atresia or congenital stenosis of the
bowel.
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| CONGENITAL INTESTINAL ATRESIA |
Atresia refers to the complete congenital obstruction of the lumen of a hollow viscus, and stenosis refers to luminal narrowing of varying degrees. The most common site of intestinal atresia is the small bowel, particularly the jejunum and ileum; the colon is least commonly affected. Intestinal atresia results from an interruption in the normal development of the gastrointestinal tract, commonly during the second and third months of fetal life. In the proximal small bowel, this is often caused by failure of the intestine to recanalize. As the intestine changes from a solid structure to a hollow tube, one or more septa may persist, leaving a diaphragm of tissue with only a minute opening and setting up a stenosis. If such persisting septa leave an intact diaphragm across the lumen, or if, during the solid stage, the intestine divides to form two or more blind segments entirely separate from each other or connected by threadlike fibrous bands, atresia ensues. In the middle and distal small bowel, atresia often results from vascular disruption, leading to ischemic necrosis of the fetal intestine. Because the fetal bowel is sterile, the necrotic tissue is resorbed, leaving blind proximal and distal ends, often with a gap in the mesentery.
Intestinal
atresia can be classified into four types based on the anatomic arrangement. In
type 1, there is no discontinuity of bowel but rather obstruction of the lumen
by a diaphragm composed of mucosa and sub-mucosa. In type 2, the proximal and
distal segments are connected by a short band and bowel discontinuity is
evident. In type 3, there is complete discontinuity. Type 4 is a combination of
types 2 and 3.
The
diagnosis of intestinal atresia or stenosis can be made with prenatal
ultrasound. Findings that suggest intestinal atresia on ultrasound include bowel
dilatation or ascites. Prenatal diagnosis can lead to prompt treatment of the
infant shortly after birth and avoids the complications associated with
intestinal obstruction.
Postnatally,
the diagnosis of intestinal atresia should be suspected in newborns that
develop abdominal distention, vomiting, or an abdominal mass with or without
obstipation. However, the timing of these signs is variable and depends on the
location of the obstruction as well as its nature, whether it is a stenosis or
an atresia. X-ray study of the abdomen is indicated in any newborn suspected to
have intestinal obstruction. The presence of persisting bile-stained vomitus in
the absence of meconium stools for more than 4 hours is often
a common initial finding in proximal obstruction. A double-bubble sign on plain
x-ray with no distal gas strongly suggests duodenal atresia. If an enema is
indicated, it should be a diagnostic barium enema, unless meconium ileus
is suspected, in which case water-soluble Gastrografin should be used. It may
be necessary to aspirate air from the stomach because it might distort or
obscure the pattern of gas distribution in the small bowel, or it may be
advisable to introduce 20 mL of gas into the stomach, if no gas is present, in
cases of obstruction in the higher parts of the small intestine.
Differentiation between the shadows of the small and large intestines is often
difficult to make, because of an underdeveloped state of the circular folds of
the jejunum as well as of the colonic haustrations. For this reason, the point
of obstruction in an infant is commonly assumed to be lower than it actually
is. Total absence of air in the abdomen is indicative of esophageal atresia
without tracheoesophageal communication. Other obstructive lesions in the
alimentary tract are, as a rule, marked by air
distention above and complete absence of air below the point of obstruction,
so, for example, in duodenal atresia the stomach and duodenum above the block
are considerably dilated, with no air below.
The
management of intestinal atresia is primarily surgical and depends on the
location of the obstruction. In all cases, the mandatory principle is to
preserve as much of the small intestine as possible. Unfortunately, in many
instances the atretic portion of the intestine is so great that lack of an
adequate absorptive surface will sometimes bring about insurmountable
difficulties in maintaining nutrition postoperatively. Preoperatively, feedings
should be withheld, the proximal segment should be decompressed after placement
of a nasoenteric tube, and fluid and electrolyte resuscitation should be
instituted promptly.
Surgery
can be performed laparoscopically; the possibility that multiple sites of
atresia may be present should be entertained and properly evaluated preoperatively,
however.
The
prognosis of intestinal atresia is very good. Most deaths occur in infants who
are premature or have associated anomalies.
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| MALROTATION OF COLON AND VOLVULUS OF MIDGUT |
Volvulus
is
the term generally used to indicate the torsion and/or coiling of an organ
about its attachment, which, in the specific case of the intestines, is the
mesentery. It may occur at all ages when, for one reason or another, an
intestinal segment becomes longer and the mesentery narrower. In the newborn, volvulus
of the midgut, which leads to serious intestinal obstruction, is a
complication of a malrotation of the colon. Normally, around week 10 of
fetal life, the ileocecal area rotates in a counterclockwise direction,
bringing the cecum into the lower right abdominal quadrant and permitting the
mesentery of the ascending colon to be fixed posteriorly and laterally to the
parietal peritoneum. Genetic mutations that disrupt signaling result in the
arrest of this process. The attachment of the mesentery from the duodenojejunal
junction to the middle of the transverse colon is lacking, causing this long
mass of intestine to remain suspended between the two points of fixation. It
may become twisted, producing not only intestinal obstruction but also
occlusion of the superior mesenteric vessels. The cecum may be held in this
abnormal position in the upper right quadrant by adventitious peritoneal
bands and be fixed to the liver, parietal peritoneum, or posterior abdominal
wall in such a way as to compress the duodenum. Peritoneal bands, not
associated with malrotation of the colon, may occasionally cause obstruction of
the duodenum or, still more rarely, of other parts of the small bowel.
The
clinical signs of these conditions are the same as those of any other cause of
intestinal obstruction in the newborn. The x-ray appearance often resembles a
typical intestinal obstruction with dilated loops proximally with completely
gas-free segments distal to the obstruction.
In
cases of volvulus, however, residual air bubbles may be observed distal to the
obstruction due to air that passed along the intestinal tract before the
volvulus occurred. During operation for these cases of volvulus of the midgut,
the twisted portion of the bowel is unwound and the Ladd procedure is carried
out on the malrotated portion. Upon severing the obstructing adventitious bands
or abnormal attachments, the colon will drop to the left side of the abdomen,
leaving the small bowel on the right
side.
Internal (e.g., paraduodenal, duodenojejunal) hernia may also be responsible for intestinal obstruction in infants. A loop of bowel may become incarcerated, or perhaps even strangulated, by entering a defect in the mesentery or by passing between adventitious bands of peritoneum. The herniation is generally diagnosed either by exclusion or on the operating table. The obvious procedure is to reduce any existing hernia and to divide any obstructing adventitious bands.
