DESCRIPTION

Hypertrophy of the muscular layers of the pylorus with elongation and thickening, leading to occlusion of the pyloric lumen and subsequent gastric outlet obstruction causing projectile nonbilious emesis

EPIDEMIOLOGY

• 1 to 4 per 1,000 live births in Western populations
• Usually presents between the 3rd and 10th week of life
• Male-to-female ratio: 4:1
• More common in White children
• Risk factors include family history, gender, younger maternal age, first born child.

ETIOLOGY

• No definitive causative factors have been identified despite considerable research.
• Genetic predisposition evidenced by variability among races, male preponderance, and genetic syndromes with pyloric stenosis
• Children of affected fathers are affected 3–5%, whereas affected mothers are associated with a 7–20% incidence.
• Several growth factors and gastrointestinal (GI) peptides, including gastrin and elevated acid levels, as well as increases in substance P, epidermal growth factor (EGF), transforming growth factor alpha (TGF α), and insulin-like growth factor-1 (IGF-1), have been implicated.
• Erythromycin may cause strong gastric and pyloric contractions that induce hypertrophy. Erythromycin exposure to lactating mothers is associated with breastfed infants who have an increased incidence of pyloric stenosis.
• Exposure to some environmental pesticides has also been implicated.
• Decreases in nerve differentiation, reduced density of neural elements, and deficiency of nitric oxide–induced muscle relaxation seem to play a role.
• Transpyloric feeding in premature infants seems to facilitate hypertrophic pyloric stenosis (HPS).
• The etiology of HPS is likely multifactorial.

PATHOPHYSIOLOGY

• Marked muscle hypertrophy and hyperplasia primarily involving the circular layer and hyperplasia of the underlying mucosa
• Growth of abnormally contorted and thickened nerve fibers and/or lack of neural elements
• Net result is either partial or complete obstruction of the pyloric channel.

COMMONLY ASSOCIATED CONDITIONS

Esophageal atresia and malrotation is noted in 5% of infants with pyloric stenosis.