Hypertrophic pyloric stenosis is obstruction of the pyloric lumen due to pyloric muscular hypertrophy. Diagnosis is by abdominal ultrasonography. Treatment is surgical.
Hypertrophic pyloric stenosis may cause almost complete gastric outlet obstruction. It affects a few out of 1000 infants and is more common among males by about a 5:1 ratio, particularly firstborn males. It occurs most often between 3 weeks and 6 weeks of age and rarely after 12 weeks.
Etiology of Hypertrophic Pyloric Stenosis
The exact etiology of hypertrophic pyloric stenosis is uncertain, but a genetic component is likely because siblings and offspring of affected people are at increased risk, particularly monozygotic twins. Maternal smoking during pregnancy also increases risk. Proposed mechanisms include lack of neuronal nitric oxide synthase, abnormal innervation of the muscular layer, and hypergastrinemia.
Some studies have noted increased risk in bottle-fed infants compared to breastfed infants, but it is not clear whether this risk is associated with a change in feeding method or with the type of feeding (1, 2).
Etiology references
1. Krogh C, Biggar RJ, Fischer TK, et al: Bottle-feeding and the Risk of Pyloric Stenosis. Pediatrics 130(4):e943-e949, 2012. doi: 10.1542/peds.2011-2785
2. McAteer JP, Ledbetter DJ, Goldin AB: Role of bottle feeding in the etiology of hypertrophic pyloric stenosis. JAMA Pediatr 167(12):1143-1149, 2013. doi: 10.1001/jamapediatrics.2013.2857
Symptoms and Signs of Hypertrophic Pyloric Stenosis
Symptoms of hypertrophic pyloric stenosis typically develop between 3 weeks and 6 weeks of life. Forceful vomiting, often described as "projectile" vomiting (without bile), occurs shortly after eating. Until dehydration sets in, children feed avidly and otherwise appear 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, children fail to gain weight, become malnourished, and develop dehydration with electrolyte and acid-base abnormalities.
Diagnosis of Hypertrophic Pyloric Stenosis
Ultrasonography
Hypertrophic pyloric stenosis should be suspected in all infants in the first several months of life with projectile vomiting, particularly if they have an appetite and otherwise appear well.
Diagnosis of hypertrophic pyloric stenosis is by abdominal ultrasonography showing increased thickness of the pylorus (typically to ≥ 4 mm; normal, < 3 mm) along with an elongated pylorus (> 16 mm).
Pearls & Pitfalls
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If the diagnosis remains uncertain, ultrasonography can be repeated serially or an upper gastrointestinal 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 (due to loss of hydrochloric acid and simultaneous hypovolemia). Approximately 5 to 14% of infants have jaundice, and about 5% have malrotation.
Treatment of Hypertrophic Pyloric Stenosis
Surgery (pyloromyotomy)
Initial treatment of hypertrophic pyloric stenosis 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.
Nonsurgical therapy is not considered a good alternative because of the efficacy and safety of pyloromyotomy.
Key Points
Projectile vomiting occurs shortly after feeding in an infant < 3 months old, usually between 3 weeks and 6 weeks of age, and, unless dehydration becomes significant, appetite tends to be intact and the infant appears well.
Diagnosis is by ultrasonography.
Treatment is surgical incision of the hypertrophied pyloric muscle.
