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Infantile hypertrophic pyloric stenosis (IHPS) remains the most common
surgical cause of nonbilious vomiting in infants.1 In
premature infants, symptoms generally begin 42 to 50 weeks of postconceptual
age. The incidence of pyloric stenosis ranges from 1 per 200 to
1 per 750 live births.
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Prospective studies have demonstrated that the pyloric muscle
is not hypertrophied at birth, but it appears
to hypertrophy after birth, leading to gastric outlet obstruction.
Proposed theories to explain the pathogenesis of infantile hypertrophic
pyloric stenosis (IHPS) include decreased nitric oxide synthase
production, altered enteric innervation, a lack of interstitial
cells of Cajal, various infectious and environmental agents, hypergastrinemia,
increased synthesis of epidermal growth factor, and congenital redundancy
of the pyloric mucosa.2,3 Certain pharmacologic
agents are known to increase the risk of IHPS in the newborn, including
prostaglandin E2 infusion or erythromycin administration.4,5
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Gastrin levels are elevated in the newborn, and postnatal infusion
of gastrin produces an identical lesion in newborn puppies, suggesting
that hypergastrinemia may play an important etiologic role. Recent
studies show a relative lack of nitric oxide (a smooth muscle relaxant)
synthase innervation, decreased density of Cajal interstitial cells,
and increased synthesis of epidermal growth factor in the hypertrophied
muscle. Despite many associations in an in vitro model, the primary
underlying cause of the disorder in an infant is still unknown.
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Mode of inheritance is polygenic and modified by sex, with the
incidence being 4 to 6 times higher in boys. Although it is believed
to be more common in first-born males, birth order seems to be less
influential than a smaller family size and higher socioeconomic
status.6 The incidence of IHPS is twofold to threefold
higher in African Americans than in those of European ancestry and
it is rare in Asians. Recently, a genomewide association demonstrated
linkage of IHPS with 2 loci on chromosomes 11q14-q22 and Xq23 that each
harbor functional candidate genes that are members of the canonical
transient receptor potential family of ion channels and have a potential
role in smooth-muscle control and hypertrophy.7
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The typical age of presentation of IHPS is between 3 to 8 weeks
old. Patients present with postprandial, forceful, nonbilious emesis,
often referred to as projectile. The infant remains hungry and eager
to feed after vomiting. When diagnosis is delayed, prolonged vomiting
may lead to dehydration, weight loss, and development of a hypochloremic
hypokalemic alkalosis. Additionally, fewer than 5% of patients
develop an unconjugated hyperbilirubinemia thought to result from
inadequate glucose absorption and an inability to maintain glucuronyl
transferase activity.
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The diagnosis of pyloric stenosis is best made by careful physical
examination in an infant with a typical history. Observation of
visible peristalsis, projectile vomiting, and palpation of a mobile
pyloric mass (the “olive”) is pathognomonic. This mass
is palpable to an experienced examiner in 80% to 90% of
cases,8 but may be difficult to ...