This obstruction results from hypertrophy
of the circular and longitudinal
muscularis of the pylorus and the distal
antrum of the stomach. It occurs
in approximately 3 of every 1000 live
births and is 4 times more common
in boys. Pyloric stenosis (PS) is relatively
uncommon in African American
and Asian infants. The observation
that it occurs primarily in first-born
infants has been disputed.
PS is seen more frequently in infants
with affected siblings or parents
than in children with no family history.
Approximately 20% of the male
and 10% of the female descendants of
mothers with congenital PS have this
condition. In contrast, PS occurs in
only 5% of males and 2.5% of females
whose fathers were affected. A multifactorial
mode of inheritance has
The hallmark of PS is progressive,
nonbilious projectile vomiting
that typically begins when the infant
is about 3 weeks old. The child is
characteristically eager to feed immediately
after vomiting. Occasionally,
there may be blood in the vomitus as
a result of gastritis or esophagitis.
The infant fails to gain--or actually
loses--weight. Approximately 2% to
5% of infants have unconjugated hyperbilirubinemia
as a result of glucuronyl
transferase deficiency secondary
to caloric deprivation.
Physical examination is best accomplished
when the infant's stomach
is empty and he or she is resting
quietly. Peristaltic waves that progress
across the upper abdomen
from left to right during feedings may
be visible. A pyloric, olive-shaped
mass that may be palpable in the
right epigastrium is pathognomonic.
As many as 7% of infants with PS
have associated malformations, such
as esophageal atresia, intestinal mal-
rotation, inguinal hernia, cryptorchidism,
or obstructive uropathy.
The differential diagnosis for
nonbilious emesis includes overfeeding,
gastroesophageal reflux, milk allergy,
adrenogenital syndrome, increased
intracranial pressure, congenital
metabolic dysfunction, prepyloric
antral web, and gastric duplication.
In the absence of a palpable pyloric
mass, abdominal ultrasonography
is the diagnostic test of choice.
The most commonly used criteria for
a positive ultrasonographic study include
pyloric muscle thickness
greater than 4 mm and pyloric channel
length greater than 14 mm. Because
these measurements are agedependent,
pyloric muscle thickness
greater than 3 mm is diagnostic for
PS in infants younger than 30 days.
If ultrasonography proves nondiagnostic,
an upper GI tract barium
study is recommended. The classic
radiographic contrast findings include
a single string sign or double railroad
track sign (produced by the narrowed
pyloric channel), a shoulder
sign (caused by the bulging of the
pyloric mass into the antrum of
the stomach), and delayed gastric
PS may be complicated by dehydration
and hypochloremic metabolic
alkalosis. The serum pH is high. The
urinary pH is high initially, but eventually
drops as the severe potassium
depletion leaves only hydrogen ions
to exchange with sodium ions in the
distal renal tubules; this results in
Fluid and electrolyte disturbances
must be corrected with intravenous
solutions before surgical intervention.
The surgical procedure of
performed through a short transverse
or periumbilical incision or laparoscopically.
On gross examination,
the pylorus appears elongated and
thickened, simulating an olive (B).
The surgeon splits the underlying pyloric
mass without cutting the mucosa
and closes the incision.
Postoperative complications are
rare. Persistent vomiting more than
48 hours after surgery suggests incomplete
myotomy or underlying gastroesophageal