This obstruction results from hypertrophyof the circular and longitudinalmuscularis of the pylorus and the distalantrum of the stomach. It occursin approximately 3 of every 1000 livebirths and is 4 times more commonin boys. Pyloric stenosis (PS) is relativelyuncommon in African Americanand Asian infants. The observationthat it occurs primarily in first-borninfants has been disputed.
This obstruction results from hypertrophyof the circular and longitudinalmuscularis of the pylorus and the distalantrum of the stomach. It occursin approximately 3 of every 1000 livebirths and is 4 times more commonin boys. Pyloric stenosis (PS) is relativelyuncommon in African Americanand Asian infants. The observationthat it occurs primarily in first-borninfants has been disputed.PS is seen more frequently in infantswith affected siblings or parentsthan in children with no family history.Approximately 20% of the maleand 10% of the female descendants ofmothers with congenital PS have thiscondition. In contrast, PS occurs inonly 5% of males and 2.5% of femaleswhose fathers were affected. A multifactorialmode of inheritance hasbeen postulated.The hallmark of PS is progressive,nonbilious projectile vomitingthat typically begins when the infantis about 3 weeks old. The child ischaracteristically eager to feed immediatelyafter vomiting. Occasionally,there may be blood in the vomitus asa result of gastritis or esophagitis.The infant fails to gain--or actuallyloses--weight. Approximately 2% to5% of infants have unconjugated hyperbilirubinemiaas a result of glucuronyltransferase deficiency secondaryto caloric deprivation.Physical examination is best accomplishedwhen the infant's stomachis empty and he or she is restingquietly. Peristaltic waves that progressacross the upper abdomenfrom left to right during feedings maybe visible. A pyloric, olive-shapedmass that may be palpable in theright epigastrium is pathognomonic.As many as 7% of infants with PShave associated malformations, suchas esophageal atresia, intestinal mal-rotation, inguinal hernia, cryptorchidism,or obstructive uropathy.The differential diagnosis fornonbilious emesis includes overfeeding,gastroesophageal reflux, milk allergy,pylorospasm, salt-wastingadrenogenital syndrome, increasedintracranial pressure, congenitalmetabolic dysfunction, prepyloricantral web, and gastric duplication.In the absence of a palpable pyloricmass, abdominal ultrasonographyis the diagnostic test of choice.The most commonly used criteria fora positive ultrasonographic study includepyloric muscle thicknessgreater than 4 mm and pyloric channellength greater than 14 mm. Becausethese measurements are agedependent,pyloric muscle thicknessgreater than 3 mm is diagnostic forPS in infants younger than 30 days.If ultrasonography proves nondiagnostic,an upper GI tract bariumstudy is recommended. The classicradiographic contrast findings includea single string sign or double railroadtrack sign (produced by the narrowedpyloric channel), a shouldersign (caused by the bulging of thepyloric mass into the antrum ofthe stomach), and delayed gastricemptying (A).PS may be complicated by dehydrationand hypochloremic metabolicalkalosis. The serum pH is high. Theurinary pH is high initially, but eventuallydrops as the severe potassiumdepletion leaves only hydrogen ionsto exchange with sodium ions in thedistal renal tubules; this results inparadoxic aciduria.Fluid and electrolyte disturbancesmust be corrected with intravenoussolutions before surgical intervention.The surgical procedure ofchoice--pyloromyotomy--can beperformed through a short transverseor periumbilical incision or laparoscopically.On gross examination,the pylorus appears elongated andthickened, simulating an olive (B).The surgeon splits the underlying pyloricmass without cutting the mucosaand closes the incision.Postoperative complications arerare. Persistent vomiting more than48 hours after surgery suggests incompletemyotomy or underlying gastroesophagealreflux.