Pediatric Hypertrophic Pyloric Stenosis

Updated: Jul 26, 2017
  • Author: Hisham Nazer, MBBCh, FRCP, DTM&H; Chief Editor: Carmen Cuffari, MD  more...
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Practice Essentials

Hypertrophic pyloric stenosis (HPS) causes a functional gastric outlet obstruction as a result of hypertrophy and hyperplasia of the muscular layers of the pylorus. In infants, hypertrophic pyloric stenosis is the most common cause of gastric outlet obstruction and the most common surgical cause of vomiting.

Signs and symptoms

Features of the history in infants with hypertrophic pyloric stenosis are as follows:

  • Typical presentation is onset of initially nonbloody, usually nonbilious vomiting at 4-8 weeks of age [1]

  • Although vomiting may initially be infrequent, over several days it becomes more predictable, occurring at nearly every feeding

  • Vomiting intensity also increases until pathognomonic projectile vomiting ensues

  • Slight hematemesis of either bright-red flecks or a coffee-ground appearance is sometimes observed

  • Patients are usually not ill-looking or febrile; the baby in the early stage of the disease remains hungry and sucks vigorously after episodes of vomiting

  • Prolonged delay in diagnosis can lead to dehydration, poor weight gain, malnutrition, metabolic alterations, and lethargy

  • Parents often report trying several different baby formulas because they (or their physicians) assume vomiting is due to intolerance

Careful physical examination provides a definitive diagnosis for most infants with hypertrophic pyloric stenosis. The diagnosis is easily made if the presenting clinical features are typical, with projectile vomiting, visible peristalsis, and a palpable pyloric tumor. Early in the course of the disease, however, some of the classic signs may be absent.

An enlarged pylorus, classically described as an "olive," can be palpated in the right upper quadrant or epigastrium of the abdomen in 60-80% of infants. [2, 3, 4]

Assessment of the pylorus requires the following:

  • The patient must be calm and cooperative; a pacifier or small amount of dextrose water may help

  • If the stomach is distended, aspiration using a nasogastric tube is necessary

  • With the infant supine and the examiner on the child's left side, gently palpate the liver edge near the xiphoid process, then displace the liver superiorly; downward palpation should reveal the pyloric olive just on or to the right of the midline

  • To be assured of the diagnosis, the physician should be able to roll the pylorus beneath the examining finger

  • The tumor (mass) is best felt after vomiting or during, or at the end of, feeding

When diagnosis is delayed, the infant may develop severe constipation associated with signs of dehydration, malnutrition, lethargy, and shock.

See Clinical Presentation for more detail.


Serum electrolytes should be measured to document adequacy of fluid resuscitation and correction of electrolyte imbalances before surgical repair. The classic biochemical abnormality in hypertrophic pyloric stenosis is hypochloremic, hypokalemic metabolic alkalosis.


  • The criterion standard imaging technique for diagnosing hypertrophic pyloric stenosis

  • Muscle wall thickness 3 mm or greater and pyloric channel length 14 mm or greater are considered abnormal in infants younger than 30 days

Barium upper GI study

  • Effective when ultrasonography is not diagnostic

  • Should demonstrate an elongated pylorus with antral indentation from the hypertrophied muscle

  • May show the "double track" sign when thin tracks of barium are compressed between thickened pyloric mucosa or the "shoulder" sign when barium collects in the dilated prepyloric antrum

  • After upper GI barium study, irrigating and removing any residual barium from the stomach is advisable to avoid aspiration


  • Reserved for patients with atypical clinical signs when ultrasonography and UGI studies are nondiagnostic

See Workup for more detail.


Hypertrophic pyloric stenosis is the most common condition requiring surgery in infancy. Correction of an associated fluid and electrolytes disturbances is vital prior to general anesthesia induction. [5] Surgical repair of hypertrophic pyloric stenosis is fairly straightforward and without many complications. However, properly preparing the infant is vitally important.

Preoperative management

  • Directed at correcting the fluid deficiency and electrolyte imbalance

  • Base fluid resuscitation on the infant's degree of dehydration

  • Most infants can have their fluid status corrected within 24 hours; however, severely dehydrated children sometimes require several days for correction

  • If necessary, administer an initial fluid bolus of 10 mL/kg with lactated Ringer solution or 0.45 isotonic sodium chloride solution

  • Continue IV therapy at an initial rate of 1.25-2 times the normal maintenance rate until adequate fluid status is achieved

  • Adequate amounts of both chloride and potassium are necessary to correct metabolic alkalosis

  • Unless renal insufficiency is a concern, initially add 2-4 mEq of KCl per 100 mL of IV fluid

  • Urine output and serial electrolyte determinations are performed during resuscitation

  • Correction of serum chloride level to 90 mEq/L or greater is usually adequate to proceed with surgical intervention

  • Before induction of anesthesia, aspirate the infant's stomach with a large-caliber suction tube to remove any residual gastric fluid or barium; saline irrigation is occasionally necessary to remove a large quantity of barium

Surgical treatment

  • Ramstedt pyloromyotomy remains the standard procedure of choice

  • The usual approach is via a right upper quadrant transverse incision that splits the rectus muscle and fascia

  • Laparoscopic pyloromyotomy may also be used [6]

  • Endoscopic pyloromyotomy is a simple procedure and can be performed as an outpatient procedure

  • Endoscopic balloon dilatation of hypertrophic pyloric stenosis after failed pyloromyotomy can be used

  • A supraumbilical curvilinear approach has gained popularity with good cosmetic results.

Postoperative management

  • Continue IV maintenance fluid until the infant is able to tolerate enteral feedings

  • In most instances, feedings can begin within 8 hours following surgery

  • Graded feedings can usually be initiated every 3 hours, starting with Pedialyte and progressing to full-strength formula

  • Schedules that advance the volume of feeds more quickly or those that begin with ad lib feeds are associated with more frequent episodes of vomiting but do not increase morbidity and actually may decrease the time to hospital discharge

  • Addition of an H2 receptor blocker sometimes can be beneficial

  • Treat persistent vomiting expectantly because it usually resolves within 1-2 days

  • Avoid the temptation to repeat ultrasonography or upper GI barium study; these invariably demonstrate a deformed pylorus, and results are difficult to interpret

See Treatment and Medication for more detail.



Hirschsprung wrote the first complete description of hypertrophic pyloric stenosis (HPS) in 1888. He believed the disease was congenital and represented fetal pyloric development failure. In 1907, Ramstedt described an operation to alleviate this condition. He suggested splitting the pyloric muscle and leaving it open to heal secondarily. This procedure has been used to treat infantile hypertrophic pyloric stenosis (IHPS) since that time. Although this curious disease is treated easily with surgery, its etiology remains undetermined. Hypertrophic pyloric stenosis is inherited by a multifactorial threshold model, and the generalized occurrence risk for siblings is 5-9%. Associated congenital anomalies are reported in 6-20% of patients with pyloric stenosis. A rare association with developmental delay has also been reported. [7]



Hypertrophic pyloric stenosis occurs secondary to hypertrophy and hyperplasia of the muscular layers of the pylorus, which cause a functional gastric outlet obstruction. Diffuse hypertrophy and hyperplasia of the smooth muscle of the antrum of the stomach and pylorus proper narrow the channel, which then can become easily obstructed. The antral region is elongated and thickened to as much as twice its normal size. In response to outflow obstruction and vigorous peristalsis, stomach musculature becomes uniformly hypertrophied and dilated. Gastritis may occur after prolonged stasis. Hematemesis is occasionally noted. The patient may become dehydrated as a result of vomiting and develop marked hypochloremic alkalosis.

Researchers have investigated the cause of this muscle hypertrophy for several decades. Many believe the problem is induced by the pyloric musculature failing to relax. Results of studies of pyloric muscle innervation are inconclusive, possibly showing a tendency toward fewer or more immature ganglion cells in affected individuals. 

No definitive cause for hypertrophic pyloric stenosis has been found. However, various environmental and hereditary factors have been implicated. Suspected environmental factors include infantile hypergastrinemia, abnormalities in the myenteric plexus innervation, cow's milk protein allergy, and exposure to macrolide antibiotics. Hereditary factors may also play a role; hypertrophic pyloric stenosis occurs in as many as 7% of infants of affected parents. The etiology is probably multifactorial, with both genetic and environmental factors contributing. Recognition that hypertrophic pyloric stenosis is an acquired disorder and not a congenital disorder is increasing. Recently, genetic studies have identified susceptibility loci for infantile hypertrophic pyloric stenosis and molecular studies have concluded that smooth muscle cells are not properly innervated in infantile HPS. [8]

Researchers who identified a cholesterol-related genetic locus associated with risk for infantile hypertrophic pyloric stenosis have also demonstrated that low serum lipids are a risk factor for this disorder. In a genome-wide association study, Feenstra and colleagues found that the single-nucleotide polymorphism (SNP) most strongly associated with risk for HPS was rs12721025 on the long arm of chromosome 11. In a follow-up study, the researchers compared levels of total cholesterol, low-density lipoprotein, high-density lipoprotein, and triglycerides in plasma obtained prospectively from 46 HPS cases and 189 control patients. Mean total cholesterol levels for cases and controls were 65.2 mg/dL and 75.2 mg/dL, respectively. The risk for IHPS was inversely and significantly associated with total cholesterol level, with an odds ratio of 0.77 per 10 mg/dL. [9, 10, 11]

In a retrospective study of pediatric data from the US military health system (MHS) spanning 11 years, investigators found that administering oral azithromycin to infants in the first 2 weeks of life increased their risk of developing hypertrophic pyloric stenosis by more than 7 fold (P < 0.001); when azithromycin was given at ages 15-42 days, the risk of developing hypertrophic pyloric stenosis was more than 2 fold (P =0.028). [12]  No cases of hypertrophic pyloric stenosis were reported among infants exposed to azithromycin between ages 43 and 90 days. [12, 13]  Further studies have reported this association along with an increased risk of developing infantile hypertrophic pyloric stenosis following the ingestion of erythromycin and azithromycin, especially in the first 14 days of life. [14, 15]  Based on these reports, monitoring for hypertrophic pyloric stenosis in infants receiving erythromycin, azithromycin, or prostaglandin infusion during the first few weeks of life is recommended. 



United States

Pyloric stenosis is the most common cause of gastric outlet obstruction in infants. It is also the most common surgical cause of vomiting in infants. The prevalence of hypertrophic pyloric stenosis ranges from 1.5-4 cases per 1000 live births among whites, although it is less prevalent among blacks and Asian Americans.



Operative therapy for hypertrophic pyloric stenosis has remained unchanged for nearly 100 years. Outcomes have improved through advances in early diagnosis, preoperative resuscitation, operative anesthetics, and nutritional management. Mortality may rarely result from late diagnosis, resulting in dehydration and shock. Mortality is also rare after pyloromyotomy. 


Reported prevalence of hypertrophic pyloric stenosis among whites ranges from 1.5-4 cases 1000 live births; hypertrophic pyloric stenosis is less prevalent among blacks, Asians, and Hispanics.


Pyloric stenosis has a well-known predilection for occurring more often in males than in females, with reported ratios ranging from 2:1 to 5:1. First-born male children are believed to have the highest risk of developing hypertrophic pyloric stenosis.


Newborns typically develop signs of gastric outlet obstruction at 3-4 weeks. Cases of hypertrophic pyloric stenosis have been documented from the first week of life to 3 months. Approximately 95% of infantile hypertrophic pyloric stenosis cases are diagnosed in those aged 3-12 weeks. Premature infants generally develop symptoms later than full-term infants, which may lead to a delay in diagnosis. Late-onset hypertrophic pyloric stenosis was reported by Wolf et al in a 17-year-old female and by Selzer D et al in a 14-year-old boy who was referred to pediatric surgery for evaluation. [16, 17] The boy in the latter report was diagnosed to have hypertrophic pyloric stenosis. He underwent laparoscopic pyloroplasty with satisfactory outcome.