INTRODUCTION — Infantile hypertrophic pyloric stenosis (IHPS) is a disorder of young infants caused by hypertrophy of the pylorus, which can progress to near-complete obstruction of the gastric outlet, leading to forceful vomiting.
The clinical manifestations, diagnosis, and treatment of IHPS are discussed below. The differential diagnosis of vomiting in infants and other related content are discussed separately. (See "Approach to the infant or child with nausea and vomiting" and "Anesthesia for pyloromyotomy in infants".)
EPIDEMIOLOGY — IHPS usually develops between three and five weeks of age and very rarely occurs after 12 weeks of age [1]. A trend toward earlier diagnosis was illustrated in a study comparing the presentation of a total of 283 infants diagnosed in the decades prior to 1975, 1985, and 1995 [2]. The mean age at presentation was significantly younger in the more recent decades (mean age 5.4 weeks in 1975 versus 3.4 weeks in 1995) [3]. The earlier diagnosis of IHPS might be explained by advances in diagnostic imaging or by increased awareness of the disorder among clinicians.
The condition occurs in approximately 1 to 3.5 per 1000 live births, although rates and trends vary markedly from region to region [4-10]. Several reports from resource-rich countries suggest a declining incidence, with variable rates [5,8,9,11].
The incidence of IHPS is associated with:
●Male sex – Male:female ratio approximately 5:1 (prevalence ratio [PR] 5.0) [4,7-9]
●Preterm birth – PR approximately 1.4 for gestational age <37 weeks [8,12-15]
●First born – PR 1.3 to 1.5 for first born compared with later birth order [8,12]
●Younger maternal age – PR approximately 1.3 for mothers <20 years, 1 for those 20 to <35 years, and 0.8 for those ≥35 years [8]
PATHOGENESIS — The etiology of IHPS is unclear but probably multifactorial, involving genetic predisposition and environmental factors [16].
Macrolide antibiotics — Both erythromycin and azithromycin are associated with increased risk of IHPS, particularly when administered to infants younger than two weeks of age [17-23]. The risk of IHPS with clarithromycin is not known [24]. (See "Pertussis infection in infants and children: Treatment and prevention", section on 'Choice of regimen'.)
In a retrospective cohort of more than 1 million infants younger than 90 days, the overall rate of IHPS was 2.29 per 1000 [17]. The risk of IHPS varied with the age of exposure to azithromycin or erythromycin, as follows:
●Azithromycin prescribed at age 0 to 14 days – Adjusted OR (aOR) 8.3, 95% CI 2.6-26.0
●Azithromycin prescribed at age 15 to 42 days – aOR 3, 95% CI 1.2-7.2
●Erythromycin prescribed at age 0 to 14 days – aOR 13.3, 95% CI 6.8-15.9
●Erythromycin prescribed at age 15 to 42 days – aOR 4.1, 95% CI 1.7-9.9
A possible association between the use of macrolide antibiotics during late pregnancy or while breastfeeding and the development of IHPS in offspring has been suggested [23,25-27] but is not supported by a meta-analysis [18].
Cases of IHPS after the use of oral macrolide antibiotics should be reported to the US Food and Drug Administration safety information and adverse event reporting program (MedWatch).
Other environmental factors
●Smoking – Maternal smoking during pregnancy increases the risk for IHPS by 1.5- to 2-fold [12,13,28-30].
●Bottle feeding – Bottle feeding is associated with increased risk for IHPS [14,28,31-35]. As an example, a large population-based study from Denmark found that bottle feeding during the first four months of life was associated with a more than fourfold increase in risk for IHPS (hazard ratio 4.62, 95% CI 2.78-7.65); a similar increase in risk was seen for infants that were both bottle- and breastfed [33]. In bottle-fed infants, similar risks were also seen in those who were never breastfed compared with those who had been formerly breastfed.
Genetic factors — Approximately 6 percent of siblings of an affected patient develop IHPS; this is approximately 30 times the rate of the general population [16].
Familial aggregation of IHPS was examined in a large population registry from Denmark, in which the rate was nearly 200-fold higher among monozygotic twins and 20-fold higher among dizygotic twins or siblings compared with individuals with no affected relatives [7]. Heritability estimates from this and one other study are 87 and 30 percent, respectively [7,36]. The maternal and paternal contributions to heritability were similar, suggesting that the intrauterine environment was not an important causal factor.
Genome-wide association studies have identified several genetic loci that confer a predisposition to IHPS, possibly implicating genes involved in lipid metabolism (eg, APOA1), as well as several genes that are highly expressed in the stomach and involved in gastrointestinal tract development (EML4, MTA3, NKX2-5, BARX1) [36].
CLINICAL MANIFESTATIONS
Typical presentation — IHPS typically presents with immediate postprandial vomiting in an infant between two and six weeks of age [1]. IHPS rarely presents after 12 weeks of age. A minority of infants present before two weeks of age, and these infants are more likely to have a positive family history of IHPS [3].
The vomiting is nonbilious and forceful ("projectile") or may become more forceful over time, with associated weight loss as symptoms progress. A minority develop electrolyte imbalances, particularly hypochloremia, due to loss of gastric hydrochloric acid [37]. The classically described "olive-like" mass in the right upper quadrant is not frequently appreciated on examination with early diagnosis of IHPS. Infants who are premature or who present very early tend to have more subtle signs and symptoms at presentation. (See 'Atypical presentation' below.)
Later presentation (classic) — If the IHPS is not diagnosed and treated in the early stages, the condition usually persists and worsens. Thus, infants who are identified later in the disease course tend to have more severe symptoms, including marked weight loss and dehydration. Classically described features are an infant demanding to be refed soon after vomiting (a "hungry vomiter") and intestinal peristalsis visible through the thin abdominal wall. Infants with prolonged symptoms may have a hypochloremic, metabolic alkalosis due to the loss of large amounts of gastric hydrochloric acid, the severity of which depends on the duration of symptoms prior to evaluation [38]. Hypokalemia is also common in infants who have been vomiting for longer than three weeks but typically is not seen in those with a more recent onset of symptoms [39].
These classic symptoms were seen in a series of 132 infants who were diagnosed with IHPS in the 1970s, in which 91 percent presented with projectile vomiting after feedings [40]. In another review of infants diagnosed between 1957 and 1969, the mean age at which the infants began vomiting was 22 days [41]. In classic reports, the frequency of palpation of the pyloric "olive" typically was quite high (up to 92 percent in a report from 1975) [40] but has been noted to be less common in subsequent reports [42-44]. This change is probably due to increasing availability and reliance on ultrasound to make the diagnosis immediately upon suspicion, so that clinicians in the modern era have less practice at palpating the pyloric "olive" [45]. In addition, infants are now more likely to be evaluated earlier in the course of the disease, when they are well nourished, which makes palpation of the "olive" more difficult. (See 'Abdominal examination' below.)
Atypical presentation
●Premature infants – The presentation of IHPS in premature infants may be more subtle: The vomiting is less forceful, infants may lack the voracious appetite and exaggerated gastric peristalsis described in term infants, and the ultrasonographic criteria for diagnosis may not apply [46-49]. Premature infants may also present at an older chronologic age compared with term infants [15,50]. One study found a mean age at presentation of 7.6 weeks in infants born prior to 34 weeks gestation versus 5.4 weeks in term infants [50]. In hospitalized premature infants, nonprojectile vomiting, weight loss, and lethargy may initially be attributed to sepsis; in this case, negative cultures, rapid improvement with intravenous fluids, and metabolic alkalosis (rather than acidosis) in such infants should prompt consideration of IHPS [46].
●Other infants – In addition to the presenting symptoms described above, the diagnosis of IHPS should be considered in young infants with repeated nonbilious vomiting, hypochloremic alkalosis, and/or rapid clinical improvement after rehydration, even in the absence of projectile vomiting or a palpable "olive" [46,47]. In a few infants with IHPS (<2 percent), the vomiting may be bilious [51].
In infants with other medical or surgical problems, the presentation may be atypical or the symptoms initially attributed to other etiologies. In infants with congenital anomalies that affect swallowing (eg, central nervous system anomalies, cleft lip and palate), vomiting may not be projectile [46]. In infants with gastrointestinal anomalies, postoperative vomiting may initially be attributed to adhesions or obstruction at an anastomotic site [46].
Clinical associations — The following clinical associations with IHPS have been described:
●Hyperbilirubinemia – Hyperbilirubinemia is one of the most frequent clinical associations of IHPS (occurring in 14 percent of cases in one series [52]). The combination of IHPS and hyperbilirubinemia is known as the icteropyloric syndrome. Unconjugated hyperbilirubinemia is more common compared with conjugated hyperbilirubinemia; it is often related to the poor hydration and nutritional status of the presenting infant and tends to resolve soon after surgical intervention [53]. In some of these cases, the unconjugated hyperbilirubinemia is an early manifestation of Gilbert syndrome, a benign condition caused by mutations in the UGT1A1 gene [52,54]. (See "Etiology and pathogenesis of neonatal unconjugated hyperbilirubinemia" and "Gilbert syndrome and unconjugated hyperbilirubinemia due to bilirubin overproduction" and 'Differential diagnosis' below.)
If the hyperbilirubinemia is conjugated, other etiologies should be considered, including liver disease or sepsis. (See "Causes of cholestasis in neonates and young infants".)
●Esophageal atresia – An association with esophageal atresia has been shown in several studies [55-58].
●Malrotation – Midgut malrotation has been described in 0.1 to 5 percent of infants with IHPS (a higher percentage than that of the general population), but it is unclear whether this is due to closer diagnostic surveillance [55,59-61]. A familial syndrome with malrotation, congenital short bowel, and IHPS also has been reported but is rare [62-64]. (See "Intestinal malrotation in children".)
●Hypoplastic frenulum – Small case series have suggested a possible association between IHPS and an absent or hypoplastic mandibular frenulum, as well as joint hypermobility [65,66]. These minor abnormalities are not functionally significant but may provide clues to the pathogenesis of the disorder. Other small case series did not find such an association [67].
Other reported associations include hiatal hernia [68], diaphragmatic hernia [61,69], congenital heart disease [55,61,70], cleft lip and palate [61], obstructive defects of the urinary tract [55], propionic acidemia [71], congenital nephrotic syndrome [72], and congenital hypothyroidism [73]. A clinical picture of IHPS was described in a one-month-old infant with familial hyperlipidemia who had an intense hyperechogenicity of the thickened pyloric muscle on ultrasound and fatty infiltration of the pyloric muscle layer at surgical exploration [74]. The symptoms resolved after implementation of a fat-restricted diet.
EVALUATION
History — The history should include details on:
●Vomiting – Vomiting in IHPS is typically projectile (very forceful) and nonbilious and tends to occur immediately after feeding. The force and timing can help to distinguish IHPS from physiologic gastroesophageal reflux, in which most episodes of vomiting are not forceful and may occur 10 minutes or more after a meal. A history of bilious vomiting does not exclude IHPS but should raise concern about more distal intestinal obstruction, such as malrotation with volvulus or Hirschsprung disease.
●Appetite – Classically, infants with IHPS have a strong appetite.
●Urine output – Low urine output (four or fewer wet diapers daily) suggests dehydration.
●Diet – Document the infant's diet and whether there were any changes prior to onset of symptoms. Vomiting that begins after a change in diet (eg, introduction of formula) or that is associated with diarrhea or bloody stools raises the possibility of a food allergy rather than IHPS. (See 'Differential diagnosis' below.)
●Medications – Exposure of the infant to macrolide antibiotics is an established risk factor for IHPS. (See 'Macrolide antibiotics' above.)
●Exposures – Acute gastrointestinal symptoms in caregivers or contacts raise the possibility of an infectious process rather than IHPS.
●Family history of IHPS – The risk of IHPS is substantially higher in infants with affected first-degree relatives. (See 'Genetic factors' above.)
Abdominal examination
●Auscultation and inspection – The abdomen should be evaluated for distension and bowel sounds. Peristaltic waves may be seen progressing across the child's upper abdomen from left to right just before emesis. Abdominal distension or high-pitched bowel sounds suggest intestinal obstruction (eg, stenosis or volvulus) rather than IHPS, especially if associated with bilious vomiting. Such infants should be evaluated promptly with abdominal radiographs.
●Palpation of the "olive" – Traditionally, the hypertrophied pylorus (known as the "olive") was palpable in 50 to 90 percent of infants with IHPS. When present, it is virtually pathognomonic of the disease (99 percent specificity in one study [75]).
The hypertrophied pylorus is felt as a firm mass at the lateral edge of the rectus abdominis muscle in the right upper quadrant of the abdomen, approximately the size and shape of an olive. To palpate it, the abdomen should be examined when the infant is quiet to avoid interference from tensed abdominal muscles; providing a pacifier dipped in a sucrose solution may be helpful to quiet the infant during the examination. Ideally, the examination should be performed immediately after an episode of emesis because the mass is less likely to be obscured by a distended antrum. As an alternative, the gastric contents can be emptied with a nasogastric tube, which helps to decompress the distended stomach and enhances the palpability of the pyloric mass.
If the "olive" is palpated, some surgeons will proceed directly to surgery, without further testing. However, in the current era, the diagnosis of IHPS is typically made or confirmed by ultrasonography. Consequently, this sign is now identified in fewer than one-third of cases [43,44].
Other physical findings — The infant should also be assessed for the following physical findings to evaluate for complications and help exclude disorders that can cause symptoms similar to IHPS:
●Weight and length – Measure weight and length to assess nutritional status, especially if the infant has had prolonged vomiting. When serial growth points are available, plotting them on a growth chart helps to establish whether there has been chronic or acute growth failure.
●Mucous membranes and skin turgor – To assess hydration.
●Skin and sclerae – Inspect for jaundice, which occurs in patients with IHPS and icteropyloric syndrome but also raises the possibility of underlying liver disease. The presence of eczema raises suspicion for a food allergy. (See 'Clinical associations' above and 'Differential diagnosis' below.)
●Stool – A stool should be visually inspected for mucus and blood and tested for occult blood. Rectal bleeding raises the possibility of cow's milk protein intolerance in a healthy-appearing infant or of intussusception in an unwell infant. Marked diarrhea raises the possibility of certain types of food allergy or infectious process (gastroenteritis). (See 'Differential diagnosis' below.)
●Genitalia – Assess for atypical genital appearance or other anomalies. Congenital adrenal hyperplasia (CAH) can present in the neonatal period with adrenal crisis, which can present with vomiting. CAH is associated with virilization of the genitalia in female infants but not in males. (See 'Differential diagnosis' below.)
Laboratory testing — In most infants with suspected IHPS, and especially in those who are ill-appearing, basic laboratory testing is appropriate to assess for dehydration and electrolyte depletion. At a minimum, the evaluation should include an electrolyte panel and complete blood count (CBC).
●Electrolytes – Interpretation is as follows:
•Normal – Patients with recent onset of symptomatic IHPS usually have normal laboratory results.
•Hypochloremic alkalosis – Low serum chloride and potassium and elevated bicarbonate are common in infants with prolonged symptoms due to IHPS. Either hypernatremia or hyponatremia may be present. One study showed that serum pH >7.45, chloride <98, and base excess >+3 gave a positive predictive value of 88 percent in diagnosing IHPS in infants presenting with vomiting [76].
•Hyperkalemic acidosis – Elevated serum potassium with low bicarbonate is not consistent with IHPS; infants with this finding should be urgently evaluated for other causes, including adrenal crisis (eg, CAH). (See 'Differential diagnosis' below.)
●Blood urea nitrogen (BUN) and creatinine – These tests help to assess for dehydration and renal insufficiency (eg, prerenal azotemia due to dehydration).
●CBC – The CBC is usually normal in infants with uncomplicated IHPS. Abnormal results do not exclude IHPS but should raise suspicion of another cause of vomiting (eg, infection).
●Bilirubin – Infants with jaundice should be evaluated for total and conjugated bilirubin, aspartate aminotransferase (AST), alanine aminotransferase (ALT), and alkaline phosphatase or gamma-glutamyl transpeptidase (GGTP).
•Elevated unconjugated bilirubin without other abnormalities is consistent with IHPS (see 'Clinical associations' above)
•Elevations in conjugated bilirubin, ALT, or AST are not consistent with IHPS and warrant further evaluation for underlying liver disease (see 'Differential diagnosis' below)
Infants who are severely dehydrated or ill-appearing may warrant further evaluation to rule out other causes including sepsis, intestinal obstruction, or a primary metabolic disorder. (See "Clinical features, evaluation, and diagnosis of sepsis in term and late preterm neonates".)
Imaging — For infants with new onset of nonbilious vomiting who are between two weeks and three months of age, with typical clinical features of IHPS, ultrasound is recommended as the first imaging modality. Plain radiographs have limited utility but can show a dilated stomach, a nonspecific finding (image 1). For infants with bilious vomiting, a fluoroscopic upper gastrointestinal (UGI) study is indicated to evaluate for malrotation with midgut volvulus (although advances in ultrasonography may allow for evaluation of these conditions). Imaging strategies for infants with vomiting are detailed by the American College of Radiology Appropriateness Criteria for infants.
Ultrasonography — Ultrasound is the preferred imaging modality for suspected IHPS. Unlike radiography, ultrasound allows for the direct visualization of the pyloric muscle and canal and also has the benefit of lack of ionizing radiation. In the hands of an experienced sonographer or radiologist, the sensitivity and specificity of ultrasonography for the diagnosis of IHPS approaches 100 percent [77-79].
The diagnosis of IHPS is based on measurements of thickness of the muscle and the length of the canal. The thickness of the muscle can be measured on a transverse view (the "target" sign (image 2)) or in the sagittal plane (image 3). A measurement above 3 mm is considered positive. The length of the pyloric canal above 18 mm also indicates IHPS [79]. If the ultrasound is negative or equivocal but the clinical picture remains concerning for IHPS, a repeat pyloric ultrasound should be considered within a few days as muscle hypertrophy can develop quickly.
There are a few potential pitfalls with ultrasound. Pylorospasm can mimic IHPS with failure of relaxation of the muscle. This is rarely a diagnostic challenge in clinical practice, but if sonographic findings are equivocal, repeat imaging can be performed after 15 to 20 minutes. Another pitfall may be the inability to visualize the pylorus due to a large amount of air within the UGI tract. Administration of water and placement of the patient in the right lateral decubitus position can provide an improved acoustic window.
More recent ultrasound techniques include direct visualization of the superior mesenteric artery and vein and identification of the third portion of the duodenum as it courses between the aorta and superior mesenteric artery. Identification of these features of normal anatomy is highly accurate in evaluating for malrotation and/or midgut volvulus [80,81].
Fluoroscopic upper gastrointestinal series — For infants with bilious vomiting, a UGI study is indicated to evaluate for intestinal malrotation and/or midgut volvulus.
Prior to the development and refinement of ultrasound, UGI was the imaging study of choice for IHPS. Fluoroscopy is less desirable due to the associated ionizing radiation and the lack of direct visualization of the pyloric muscle. If UGI is performed in an infant with IHPS, narrowing of the canal can be seen (the "string" sign) or pointing of the barium at the pyloric canal (the "beak" sign) (image 4). An impression on the gastric antrum from the hypertrophied muscle (the "shoulder" sign) can also be seen. Pylorospasm can mimic the findings of IHPS with a UGI, and a suspicious UGI should be confirmed with a pyloric ultrasound.
Upper endoscopy — Upper endoscopy usually is reserved for patients in whom other imaging modalities are inconclusive (or if warranted to evaluate for another gastrointestinal disorder because of symptoms or signs that are atypical for IHPS). In infants with IHPS, the mucosa of the antrum and pylorus appear thickened [82]. Endoscopy is useful for obtaining tissue sample if eosinophilic gastritis is suspected, which can mimic IHPS.
DIAGNOSIS — The diagnosis of IHPS is suspected when an infant presents with suggestive features, as described above. The diagnosis can be confirmed by palpation of an "olive" or by the presence of typical findings on imaging studies. In many centers, ultrasonography is performed to confirm the diagnosis of IHPS prior to surgery, even if an "olive" is palpated. (See 'Evaluation' above.)
DIFFERENTIAL DIAGNOSIS — The differential diagnosis of vomiting in early infancy includes the following disorders (table 1). In most cases, these are easily distinguished from IHPS by the history, physical examination, and/or initial laboratory tests. (See "Approach to the infant or child with nausea and vomiting", section on 'Disorders primarily seen in neonates and young infants'.)
●Gastroesophageal reflux – Physiologic reflux in newborns and infants is common and is characterized by effortless regurgitation in an otherwise healthy infant (a "happy spitter"). The regurgitation may seem forceful at times. Physiologic reflux is not associated with electrolyte abnormalities, tends to be chronic rather than progressive, and rarely causes weight loss. (See "Gastroesophageal reflux in infants".)
●Food allergy – Several distinct gastrointestinal disorders in children are caused by immunologic reactions to dietary proteins. Considerations for an infant with vomiting include immunoglobulin E (IgE)-mediated food allergy, food protein-induced enterocolitis syndrome, food protein-induced enteropathy, and food protein-induced proctocolitis. Clinical features and distinguishing characteristics of these disorders are outlined separately. (See "Milk allergy: Clinical features and diagnosis", section on 'Clinical features'.)
●Gastric or duodenal inflammatory disease – Eosinophilic gastritis or peptic ulcers can cause gastric outlet obstruction that mimics the symptoms of IHPS [83-88]. These disorders are uncommon in young infants but have been reported. Suggestive findings are lack of pyloric muscle hypertrophy on ultrasound; the definitive diagnosis requires endoscopy.
●Adrenal crisis – Newborn infants with adrenal insufficiency may present with an adrenal crisis, manifested by vomiting and dehydration. This is a life-threatening condition and should be evaluated and treated urgently. Key features of adrenal crisis are disproportionate hypotension and hyperkalemic acidosis (rather than the hypokalemic alkalosis typically seen in IHPS). The most common cause of adrenal insufficiency in infants is congenital adrenal hyperplasia (CAH). Females with CAH tend to have virilized or ambiguous genitalia; males usually have no obvious genital abnormalities. (See "Clinical manifestations and diagnosis of adrenal insufficiency in children", section on 'Adrenal crisis'.)
●Intestinal obstruction – Causes of intestinal obstruction in early infancy include malrotation (with or without volvulus), intussusception, congenital antral web, and Hirschsprung disease. Intestinal obstruction should be considered in infants with bilious vomiting and abdominal distension, especially if high-pitched bowel sounds or bloody stools are present. If intestinal obstruction is suspected, the specific diagnosis is often suggested by the patient's history and then confirmed with appropriate radiologic imaging, including a plain radiograph. (See "Approach to the infant or child with nausea and vomiting", section on 'Intestinal obstruction'.)
●Liver disease – Liver disease in infants may present with symptoms resembling IHPS, including vomiting, poor weight gain, and jaundice. Infants with biliary atresia also may have acholic (very pale-colored) stools. Infants with conjugated hyperbilirubinemia should be further evaluated for liver disease, including biliary atresia, biliary cysts, and metabolic disorders. (See "Causes of cholestasis in neonates and young infants" and "Approach to evaluation of cholestasis in neonates and young infants".)
Evaluation of isolated elevated unconjugated bilirubin in a young infant is discussed separately. (See "Evaluation of jaundice caused by unconjugated hyperbilirubinemia in children".)
TREATMENT — Definitive management of IHPS is surgical pyloromyotomy. The timing of surgery depends on the clinical status of the infant. If the child is well hydrated with normal electrolytes, and if surgeons with expertise in the procedure are available, surgery may take place on the day of diagnosis [89]. Surgery should be delayed in the setting of dehydration and/or electrolyte derangements [90].
Preoperative fluid and electrolyte management — Fluid and electrolyte therapy should be individualized according to the degree of dehydration and/or electrolyte abnormalities.
●Normal electrolytes with mild or no dehydration – Infants presenting with normal electrolyte values and mild or no dehydration, as is the case with >60 percent of patients, should receive maintenance intravenous fluids. (See "Maintenance intravenous fluid therapy in children".)
●Moderate or severe dehydration – Infants with moderate or severe dehydration require more intensive management by administering isotonic fluids (typically normal saline [0.9% NaCl]), given as an initial fluid bolus and/or higher rates of administration (1.5 to 2 times maintenance) until the calculated fluid deficit is repleted, followed by maintenance intravenous fluids. Renal function should be assessed before adding potassium to the intravenous fluids. (See "Treatment of hypovolemia (dehydration) in children".)
We suggest the following targets for fluid and electrolyte therapy prior to undergoing surgery, as recommended by an expert panel [91]:
•pH ≤7.45 and/or base excess ≤3.5
•Bicarbonate <26 mEq/L
•Sodium ≥132 mEq/L
•Potassium ≥3.5 mEq/L
•Chloride ≥100 mEq/L
•Glucose ≥72 mg/dL (4.0 mmol/L)
Infants with significant alkalosis at the time of surgery are at increased risk of postoperative apnea [92,93]. Patients with severe hypokalemia (serum potassium <2.5 mEq/L) or hyponatremia (serum sodium <120 mEq/L) are at particularly high risk for perioperative complications and should be managed carefully, with expert consultation if needed. (See "Hypokalemia in children" and "Hyponatremia in children: Evaluation and management".)
Pyloromyotomy
●Technique – The classical operation for IHPS is Ramstedt pyloromyotomy, which involves a longitudinal incision of the hypertrophic pylorus with blunt dissection to the level of the submucosa; it relieves the constriction and allows normal passage of stomach contents into the duodenum. Laparoscopic pyloromyotomy (picture 1) is a minimally invasive version of the Ramstedt procedure. In settings where appropriately trained surgical expertise is available, we suggest laparoscopic pyloromyotomy rather than the open procedure. Laparoscopic pyloromyotomy is associated with a lower incidence of postoperative emesis, reduced need for analgesia, and shorter hospital stay; however, it occasionally results in incomplete pyloromyotomy or mucosal perforation [94-97]. A transumbilical approach also may be used but has longer operating time [98].
Open and laparoscopic pyloromyotomy were compared in a prospective randomized trial in 200 infants with ultrasonographically confirmed IHPS [94]. Both groups had similar operating time, time to full feeding, and hospital length of stay. However, infants in the laparoscopic group had fewer episodes of emesis (1.9 versus 2.6) and received fewer doses of analgesia (1.6 versus 2.2) compared with those in the open group. A similar randomized study also reported more rapid return to enteral feeding and shorter hospital stay among infants treated laparoscopically, although in 3 percent of laparoscopically performed cases, the pyloromyotomy was incomplete [95]. The study was performed at six centers with extensive experience in laparoscopic techniques.
Anesthesia for pyloromyotomy is discussed separately. (See "Anesthesia for pyloromyotomy in infants".)
●Resuming feeds postoperatively – For most infants, we suggest resuming ad lib feeding early (within a few hours) after surgery rather than delaying feeding and slowly advancing. Modest regurgitation occurs in as many as 80 percent of infants after pyloromyotomy [40] and should not delay feedings. Vigorous postoperative vomiting is infrequent. If vomiting persists beyond five days postoperatively, radiologic evaluation should be performed [99], with the understanding that interpretation of the study may be difficult because of postoperative swelling.
The practice of resuming ad lib feeds in the early postoperative setting is supported by observational studies, clinical trials, and meta-analyses [100-102]. The meta-analysis included 14 studies (11 observational studies and 3 randomized trials) and concluded that ad lib feeding was associated with shorter duration of hospitalization compared with structured feeding (mean difference 4.7 days, 95% CI 1-8.4 days) [100]. In the four included studies examining early versus late feeding, early feeding was associated with a greater likelihood of postoperative emesis (odds ratio 3.1, 95% CI 2.3-4.4), but the duration of hospitalization was shorter (mean difference 12 hours); however, the latter finding was not statistically significant (95% CI 8 hours longer to 32 hours shorter).
●Postoperative monitoring – Infants with IHPS are at risk for apnea postoperatively because of their young age and effects of anesthesia; we suggest monitoring for apnea for at least 24 hours postoperatively. Those with underlying alkalosis may be at increased risk, based on limited and inferential data [93]. As mentioned above, this is one reason why alkalosis and other electrolyte abnormalities should be corrected prior to surgery.
●Complications – The rate of serious complications from pyloromyotomy is low. Mucosal perforations occur in <1 percent of patients and are readily recognized intraoperatively [103]. The pyloromyotomy is incomplete in approximately 1 to 3 percent of patients treated with a laparoscopic approach by an experienced surgeon and is even rarer in those undergoing the open procedure [94,95,103].
●Follow-up – Infants should be monitored through surgical recovery and return to normal feeds. Thereafter, they need only routine pediatric care, including monitoring of growth, unless new symptoms develop. Infants with other persistent or recurrent symptoms warrant further evaluation, including for disorders other than IHPS. If abdominal ultrasonography is performed postoperatively, caution should be exercised in interpretation because the thickened muscle and enlarged diameter persist to eight months and one year, respectively [104].
Other approaches (not recommended) — Because surgery is both safe and effective, alternative approaches to managing IHPS are generally limited to infants with very high surgical risks or situations where pediatric surgical care is not available.
●Atropine – Treatment with intravenous and/or oral atropine sulfate (which relaxes the pyloric musculature) has been described in small observational studies [105-108] and two meta-analyses [109,110]. In a meta-analysis, the pooled success rate using atropine was 79 percent [110]. However, this approach typically requires weeks or months of atropine with parenteral nutrition or postpyloric enteral feeds, as well as prolonged hospital stay [110,111].
●Conservative management – Conservative management of infants with IHPS has also been described. This approach typically involves a trial of continuous nasoduodenal feedings, generally lasting several months, until the gastric outlet obstruction diminishes as the infant grows [112].
●Balloon dilation – Endoscopically guided balloon dilation for IHPS has been described [113]. However, balloon dilatation does not reliably disrupt the seromuscular ring of the pylorus and is associated with a significant risk of pyloric perforation [114].
OUTCOMES — Pyloromyotomy is curative in the vast majority of infants [103]. Gastroesophageal reflux in patients previously treated for IPHS is common, as it is in other healthy infants, and does not warrant concern unless it is very severe or accompanied by other symptoms. (See "Gastroesophageal reflux in infants".)
In long-term follow-up, individuals who underwent pyloromyotomy as infants had no clinically significant differences in gastroesophageal reflux or other gastrointestinal symptoms during adulthood compared with age- and sex-matched controls [115]. Similarly, most studies show normal gastric emptying despite altered pyloric tone and motility in long-term follow-up [116].
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Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Basics topic (see "Patient education: Pyloric stenosis in babies (The Basics)")
SUMMARY AND RECOMMENDATIONS
●Pathogenesis – Infantile hypertrophic pyloric stenosis (IHPS) is characterized by hypertrophy of the pylorus, eventually progressing to near-complete obstruction of the gastric outlet. The etiology of IHPS is obscure but probably multifactorial, involving genetic predisposition and environmental factors. In particular, IHPS has been associated with the administration of macrolide antibiotics to infants during the first few weeks of life and perhaps to their mothers during late gestation or lactation. (See 'Pathogenesis' above.)
●Clinical presentation – Symptoms usually begin between three and five weeks of age and very rarely occur after 12 weeks of age. Typical presenting symptoms are nonbilious vomiting that is forceful and occurs immediately after feeding, while the infant remains hungry. In a small percentage of infants, the vomiting may be bilious. In premature infants with IHPS, the vomiting may be less forceful and they may not display hunger. A firm, "olive-like" mass is occasionally palpable in the right upper quadrant of the abdomen, and there may be signs of dehydration. (See 'Clinical manifestations' above.)
●Evaluation – Evaluation of an infant with suspected IHPS includes:
•Physical examination – A firm, "olive-like" mass may be palpable in the right upper quadrant of the abdomen, and there may be signs of dehydration.
•Laboratory testing – Measure electrolytes and complete blood count (CBC) to assess for dehydration and electrolyte depletion. Infants with IHPS may have normal results or may have low serum chloride and potassium and elevated bicarbonate (a hypochloremic alkalosis). (See 'Laboratory testing' above.)
•Imaging – The diagnosis of IHPS is almost always confirmed by imaging, and ultrasonography is the modality of choice. Hallmarks of the diagnosis are increased thickness to the pyloric muscle and elongation of the pyloric canal (image 3). For infants who present with bilious vomiting, a fluoroscopic upper gastrointestinal (UGI) study is indicated to evaluate for intestinal malrotation and/or midgut volvulus, although more recent advances in ultrasonography may allow for evaluation for these conditions. (See 'Imaging' above.)
●Differential diagnosis – The differential diagnosis of IHPS includes physiologic gastroesophageal reflux and cow's milk protein intolerance, which are relatively benign. More severe disorders that may present with vomiting in the first two months of life include adrenal crisis, intestinal obstruction (eg, due to malrotation, Hirschsprung disease, or intussusception), and liver disease (eg, biliary atresia or metabolic defects). These disorders should be considered in infants with atypical presenting features, including hypotension, vomiting that is bilious, abdominal distension, or jaundice with conjugated hyperbilirubinemia (table 1). (See 'Differential diagnosis' above.)
●Treatment – IHPS is treated surgically. (See 'Pyloromyotomy' above.)
•Timing of surgery – If the child is well hydrated with normal electrolytes, and if surgeons with expertise in the procedure are available, surgery may take place on the day of diagnosis.
For infants with moderate to severe dehydration and/or electrolyte derangements, surgery should be delayed until these abnormalities are corrected. (See 'Preoperative fluid and electrolyte management' above.)
•Surgical technique – In settings where appropriate surgical expertise is available, we suggest laparoscopic rather than open pyloromyotomy (Grade 2B). Laparoscopic pyloromyotomy is associated with a lower incidence of postoperative emesis, reduced need for analgesia, and shorter hospital stay. Complication rates are low with both procedures. (See 'Pyloromyotomy' above.)
•Postoperative feeds – For most infants, we suggest resuming ad lib feeding early (within a few hours) after surgery rather than delaying feeding and slowly advancing (Grade 2C). Feeds should not be delayed by mild regurgitation. (See 'Pyloromyotomy' above.)
•Alternatives if surgery cannot be performed – Because surgery is both safe and effective, alternative approaches to managing IHPS are generally limited to infants with very high surgical risks or situations where pediatric surgical care is not available. Options include conservative management with nasoduodenal feeds, with or without atropine. (See 'Other approaches (not recommended)' above.)
