Ronald I. Paul
• Pyloric stenosis presents most commonly at 5 to 6 weeks of age.
• Progressive nonbilious projectile vomiting is the most common presenting symptom.
• The typical electrolyte imbalance is hypochloremic metabolic alkalosis.
• Diagnosis is confirmed by ultrasound, and rarely by a fluoroscopic upper GI contrast study.
• Treatment is surgical pyloromyotomy.
Pyloric stenosis, also known as hypertrophic pyloric stenosis, is a condition affecting young infants in which the pylorus muscle becomes abnormally thickened, causing obstruction to gastric emptying. It is most often seen in the first few weeks of life. The most common age at presentation is between 5 and 6 weeks with a range of 2 to 31 weeks.1,2 Although premature infants may present later than term babies (6 weeks compared with 5 weeks), their presentation is actually earlier when measured from postmenstrual age (40 weeks vs. 45 weeks).2 Its incidence has been reported to be 3 per 1000 live births in the Western World. Lower incidence ranges have been reported for Asian children, with reports between 0.3 to 0.5 per 1000 infants in Taiwanese infants.3,4 A recent decline in pyloric stenosis has been reported both in the United States and several European countries concurrent with a declining incidence of sudden infant death syndrome, leading to some belief that recommended supine sleeping position may be responsible for both declines.5 A genetic predisposition has been noted with an increased incidence of siblings and a strong increased incidence in twins, both monozygotic and dizygotic.6,7 It is unclear if the increased incidence in twins is due to genetic or environmental causes. Genetic tests have identified a number of potential loci and further studies are ongoing.8,9 There is nearly a four-to fivefold male predominance and an increased incidence in premature infants.2 The highest incidence reported is in first-born infants, although this may be due to more families having only one child than two or three children.9,10 Environmental and mechanical factors have been implicated as potential causes. Infants that were breastfed exclusively have a much lower risk of developing pyloric stenosis compared with infants that have been bottle-fed or bottle-fed and breastfed.11 Very early exposure to erythromycin has been associated with a nearly eightfold increased risk of developing pyloric stenosis.12,13 Erythromycin is a motilin agonist, and thus it produces strong gastric and pyloric contractions. Infants exposed to erythromycin through breast milk may also be at risk for developing pyloric stenosis, but the data are not as conclusive.14 It is unclear if other macrolide antibiotics like azithromycin are also associated with increased risk, although there are case reports where infants treated with azithromycin have developed pyloric stenosis.15
SIGNS AND SYMPTOMS
The key to diagnosing pyloric stenosis remains a comprehensive history and physical examination, with confirmation by ultrasound. The diagnosis should be considered in any young infant with a history of repeated vomiting. The mean duration of symptoms prior to diagnosis is 8 days; however, it can range from 1 day to 13 weeks.1,2 A classic triad of projectile vomiting, palpable olive, and visible peristalsis on feeding has been described with pyloric stenosis.1,2 Projectile vomiting typically occurring immediately after feeding is reported in nearly all cases. Infants will not have anorexia and are often described as hungry. They generally appear well, depending on the level of hydration. It ranges from normal to severe dehydration depending upon the duration of symptoms. A palpable olive in the right upper quadrant used to be present in the majority of cases in earlier decades, but is uncommon now, present in only 13% in a recent study, likely due to earlier diagnosis.1 Peristaltic gastric waves may be seen in infants with advanced disease and dehydration but has recently been reported in only 25% of cases.2,16 Although the majority of infants have nonbilious vomiting, a small percentage of infants present with bilious emesis and hematemesis.17
Electrolyte and blood gas measurements may show classic imbalances including hypochloremia and metabolic alkalosis. Similar to the disappearing palpable olive, recent studies demonstrate that laboratory abnormalities are less common than in the past, with hypochloremia now present in 23% and alkalosis present in 21% of patients with pyloric stenosis.1 Patients are generally depleted of total potassium as well, although the serum potassium level is usually normal.18
Diagnosis of pyloric stenosis can be confirmed with either ultrasound or a fluoroscopic upper GI contrast study.19 Ultrasound is the diagnostic imaging procedure of choice. There is a range in the literature for criteria for diagnosis by ultrasound, which includes a pylorus muscle thickness of 3 to 4 mm or higher, and a pyloric length of 15 to 19 mm or higher20–22 (Fig. 46-1). Additional criteria include no visualized flow of gastric content through a dilated pylorus. Muscle thickness and length have shown correlation with age and weight. Patients that are smaller and younger may have a clinical diagnosis and not meet minimal diagnostic criteria for ultrasound diagnosis.23 Point-of-care ultrasound by emergency physicians and surgeons have been reported and have shown success in confirming the diagnosis.24–26 Because the development of pyloric stenosis is a progressive process, an initial negative ultrasound may need to be repeated later if symptoms persist.27
FIGURE 46-1. Ultrasound image of thickened pylorus muscle with length measured at 15 mm.
Although no longer the standard method for diagnosing pyloric stenosis in most centers, upper GI contrast fluoroscopy is still used by some without access to skilled ultrasonographers, or when the study is done to evaluate for other diagnoses. The diagnosis is confirmed by observing contrast propelled through a narrowed and obstructed pyloric channel.19 Two classic findings with an upper GI contrast fluoroscopy have been described including a string sign caused by the hypertrophic pylorus muscle and extension of the pylorus muscle into the stomach resembling an appearance of shoulders18,19 (Fig. 46-2). To accurately see the contrast leaving the stomach, the infant should have nothing to eat for several hours prior to the study or have gastric contents removed by an orogastric tube. Upper GI contrast fluoroscopy is considered accurate, albeit more invasive than an ultrasound with the potential for vomiting and aspiration. It involves protracted fluoroscopy time and therefore more radiation than an ultrasound. An Upper GI series can provide additional information if other diagnoses are being considered such as gastroesophageal reflux, duodenal web, or malrotation.
FIGURE 46-2. Upper GI image of thickened pylorus muscle demonstrating “string sign.”
Initial management includes correction of fluid and electrolyte abnormalities if present, and referral to a pediatric surgeon. Surgical repair, pyloromyotomy,18 was first developed by Conrad Ramstedt in 1911 and remains the treatment of choice.28 Recently, laparoscopic pyloromyotomy has been instituted at some institutions and may provide clinical benefits including reduced time for initiation of feeding.29 With either procedure, infant feeding is usually begun within several hours.30
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25. McVay MR, Copeland DR, McMahon LE, et al. Surgeon-performed ultrasound for diagnosis of pyloric stenosis is accurate, reproducible, and clinically valuable. J Pediatr Surg. 2009;44:169.
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28. Georgoula C, Gardiner M. Pyloric stenosis a 100 years after Ramstedt. Arch Dis Child. 2012;97:741.
29. Carrington EV, Hall NJ, Pacilli M, et al. Cost-effectiveness of laparoscopic versus open pyloromyotomy. J Surg Res. 2012;178:315.
30. Juang D, Adibe OO, Laituri CA, et al. Distribution of feeding styles after pyloromyotomy among pediatric surgical training programs in North America. Eur J Pediatr Surg. 2012;22:409.