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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 ...

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