Hypertrophic pyloric stenosis is obstruction of the pyloric lumen due to pyloric muscular hypertrophy. Diagnosis is by abdominal ultrasound. Treatment is with pyloromyotomy.
Hypertrophic pyloric stenosis may cause almost complete gastric outlet obstruction.
This disorder affects 2 to 5 of 1000 infants and is more common among males by approximately a 5:1 ratio, particularly firstborn males (1). It manifests most often between 3 weeks and 6 weeks of age and rarely after 12 weeks.
General reference
1. MacMahon B. The continuing enigma of pyloric stenosis of infancy: a review. Epidemiology. 2006;17(2):195-201. doi:10.1097/01.ede.0000192032.83843.c9
Etiology of Hypertrophic Pyloric Stenosis
The exact etiology of hypertrophic pyloric stenosis is uncertain, but the condition is highly heritable, and multiple genes have been implicated in association studies (1–3). Maternal smoking during pregnancy also increases risk (4). Proposed mechanisms include lack of neuronal nitric oxide synthase, abnormal innervation of the muscular layer, and hypergastrinemia.
Infants exposed to certain macrolide antibiotics (eg, erythromycin) in the first few weeks of life are at significantly increased risk (5, 6).
Studies have shown increased risk in bottle- and formula-fed infants compared to exclusively breastfed (chestfed) infants, but it is not clear whether this risk is associated with a change in feeding method or with the type of feeding (7–9).
Etiology references
1. Krogh C, Fischer TK, Skotte L, et al. Familial aggregation and heritability of pyloric stenosis. JAMA. 2010;303(23):2393-2399. doi:10.1001/jama.2010.784
2. Feenstra B, Geller F, Krogh C, et al. Common variants near MBNL1 and NKX2-5 are associated with infantile hypertrophic pyloric stenosis. Nat Genet. 2012;44(3):334-337. Published 2012 Feb 5. doi:10.1038/ng.1067
3. Fadista J, Skotte L, Geller F, et al. Genome-wide meta-analysis identifies BARX1 and EML4-MTA3 as new loci associated with infantile hypertrophic pyloric stenosis. Hum Mol Genet. 2019;28(2):332-340. doi:10.1093/hmg/ddy347
4. Obaid YY, Toubasi AA, Albustanji FH, Al-Qawasmeh AR. Perinatal risk factors for infantile hypertrophic pyloric stenosis: A systematic review and meta-analysis. J Pediatr Surg. 2023;58(3):458-466. doi:10.1016/j.jpedsurg.2022.08.016
5. Abdellatif M, Ghozy S, Kamel MG, et al. Association between exposure to macrolides and the development of infantile hypertrophic pyloric stenosis: a systematic review and meta-analysis. Eur J Pediatr. 2019;178(3):301-314. doi:10.1007/s00431-018-3287-7
6. Eberly MD, Eide MB, Thompson JL, Nylund CM. Azithromycin in early infancy and pyloric stenosis. Pediatrics. 2015;135(3):483-488. doi:10.1542/peds.2014-2026
7. Krogh C, Biggar RJ, Fischer TK, et al. Bottle-feeding and the Risk of Pyloric Stenosis. Pediatrics. 2012;130(4):e943-e949. doi:10.1542/peds.2011-2785
8. McAteer JP, Ledbetter DJ, Goldin AB. Role of bottle feeding in the etiology of hypertrophic pyloric stenosis. JAMA Pediatr. 2013;167(12):1143-1149. doi:10.1001/jamapediatrics.2013.2857
9. Wayne C, Hung JH, Chan E, Sedgwick I, Bass J, Nasr A. Formula-feeding and hypertrophic pyloric stenosis: is there an association? A case-control study. J Pediatr Surg. 2016;51(5):779-782. doi:10.1016/j.jpedsurg.2016.02.021
Symptoms and Signs of Hypertrophic Pyloric Stenosis
Symptoms of hypertrophic pyloric stenosis typically develop between 3 weeks and 6 weeks of life. Forceful or projectile nonbilious emesis 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 do not gain weight, become malnourished, and develop dehydration with electrolyte and acid-base abnormalities (hypochloremic, hypokalemic metabolic alkalosis).
Diagnosis of Hypertrophic Pyloric Stenosis
Ultrasound
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 is by abdominal ultrasound showing increased thickness of the pylorus (typically to ≥ 3 mm; normal, < 3 mm) along with an elongated pylorus (1).
Pearls & Pitfalls
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If the diagnosis remains uncertain, ultrasound can be repeated serially or an upper gastrointestinal (GI) series can be performed. The upper GI series 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/hypokalemic metabolic alkalosis due to direct loss of hydrochloric acid and intravascular volume depletion leading to activation of the renin-angiotensin-aldosterone system, which causes increased renal potassium excretion in exchange for sodium. Up to 14% of infants have jaundice (icteropyloric syndrome).
Diagnosis reference
1. Expert Panel on Pediatric Imaging, Alazraki AL, Rigsby CK, et al. ACR Appropriateness Criteria® Vomiting in Infants. J Am Coll Radiol. 2020;17(11S):S505-S515. doi:10.1016/j.jacr.2020.09.002
Treatment of Hypertrophic Pyloric Stenosis
Pyloromyotomy
Initial treatment of hypertrophic pyloric stenosis is directed at fluid resuscitation 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. Some centers are now successfully performing endoscopic pyloromyotomy (1). Pyloromyotomy is safe and effective.
Treatment reference
1. Zhang H, Liu Z, Ma L, et al. Gastric Peroral Endoscopic Pyloromyotomy for Infants With Congenital Hypertrophic Pyloric Stenosis. Am J Gastroenterol. 2023;118(3):465-474. doi:10.14309/ajg.0000000000001973
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 ultrasound.
Treatment is surgical incision of the hypertrophied pyloric muscle (pyloromyotomy).
