Hypertrophic pyloric stenosis is obstruction of the pyloric lumen due to pyloric muscular hypertrophy.

Hypertrophic pyloric stenosis may cause almost complete gastric outlet obstruction. It affects 1 of 250 infants and is more common among males by a 4:1 ratio, particularly firstborn males. It occurs most often between 3 to 5 wk of age and rarely after 12 wk. The exact etiology is uncertain, but a genetic component is likely because siblings and offspring of affected people are at increased risk. Proposed mechanisms include lack of neuronal nitric oxide synthase and abnormal innervation of the muscular layer. Infants exposed to certain macrolide antibiotics in the first few weeks of life are at significantly increased risk.

Symptoms and Signs

Symptoms can develop between 2 and 6 wk of life. Projectile vomiting (without bile) occurs shortly after eating. Until dehydration sets in, the child feeds avidly and otherwise appears well, unlike many of those with vomiting caused by systemic illness. Gastric peristaltic waves may be visible, crossing the epigastrium from left to right. A discrete, 2- to 3-cm, firm, movable, and olive-like pyloric mass is sometimes palpable deep in the right side of the epigastrium. With progression of illness, the child fails to gain weight, and signs of dehydration (see Dehydration and Fluid Therapy in Children: Symptoms and Signs) appear.

Diagnosis

Diagnosis is by abdominal ultrasonography showing increased thickness of the pylorus (typically to ≥ 4 mm; normal, < 2 mm) along with an elongated pylorus (> 16 mm). If the diagnosis remains uncertain, ultrasonography can be repeated serially or an upper GI series can be done, which typically shows delayed gastric emptying and a “string” sign or “railroad track” sign of a markedly narrowed, elongated pyloric lumen. In rare cases, upper endoscopy is required for confirmation. The classic electrolyte pattern of an infant with pyloric stenosis is that of hypochloremic metabolic alkalosis. About 5% of infants are jaundiced.

Treatment

Initial treatment is directed at hydration and correcting electrolyte abnormalities. Definitive treatment is a longitudinal pyloromyotomy, which leaves the mucosa intact and separates the incised muscle fibers. Postoperatively, the infant usually tolerates feeding within a day.

Last full review/revision November 2007 by William J. Cochran, MD

Content last modified February 2012