1 Infantile hypertrophic pyloric stenosis

UpToDate 2007
Infantile hypertrophic pyloric stenosis

Anthony P Olivé, MD
Erin E Endom, MD
INTRODUCTION — Infantile hypertrophic pyloric stenosis (IHPS) is a condition of hypertrophy of the pylorus, with elongation and thickening, eventually progressing to near-complete obstruction, of the gastric outlet. It occurs in approximately 2 to 3.5 in 1000 live births [ 1-5], more commonly in males (4:1 to 6:1) [ 1,6-9]. Approximately 30 percent of cases occur in firstborn children [ 6,7,10].
ETIOLOGY — The etiology of IHPS is obscure but probably is multifactorial, involving genetic predisposition and environmental factors. Neonatal hypergastrinemia and gastric hyperacidity may have a role [ 8], as may increased vascularity [ 11].
Macrolide antibiotics — An association between IHPS and the administration of oral erythromycin given for postexposure prophylaxis for pertussis has been described [ 12,13]. The greatest risk appears to occur in infants given the medication within the first two weeks of life [ 14,15].
It is not known if clarithromycin and azithromycin pose the same risks for IHPS [ 16]. However, an association between IHPS and the use of macrolide antibiotics among breastfeeding women also has been described, and is particularly strong among female offspring [ 17].
Cases of pyloric stenosis after the use of oral erythromycin should be reported to the FDA safety information and adverse event reporting program (MedWatch, www.fda.gov/medwatch).
CLINICAL MANIFESTATIONS —
Classic presentation — The classic presentation of IHPS is the three- to six-week-old baby who develops immediate postprandial, non-bilious, often projectile vomiting and demands to be re-fed soon afterwards (a "hungry vomiter"). In a 13-year review of 132 infants, 91 percent presented with projectile vomiting after feedings [ 6]. The majority (83 percent) were boys, and 31 percent were firstborn. In another review of infants diagnosed between 1957 to 1969, the mean age in which the infants began vomiting was 22 days [ 18].
Patients were classically described as being emaciated and dehydrated with a palpable "olive-like" mass at the lateral edge of the rectus abdominus muscle in the right upper quadrant of the abdomen. The frequency of palpation of the "olive" typically was quite high (up to 92 percent) in a report from 1975 [ 6], but is less common subsequent reports [ 19]. The "olive" is most easily felt immediately after emesis because it may otherwise be obscured by a distended antrum and/or tensed abdominal muscles. Peristaltic waves may be seen progressing across the child's upper abdomen from left to right just before emesis.
Laboratory evaluation classically showed a hypochloremic, metabolic alkalosis resulting from the loss of large amounts of gastric hydrochloric acid, the severity of which depended upon the duration of symptoms prior to initial evaluation [ 20]. Similarly, hypokalemia typically is not seen early on but is quite common in babies who have been vomiting for longer than three weeks [ 21].
The typical presentation has changed over time. Infants are diagnosed earlier than in the past, tend to be better nourished, and generally present without significant electrolyte imbalances. This difference was illustrated in a study comparing the presentation of a total of 283 infants diagnosed in the decades prior to 1975, 1985, and 1995 [ 22]. The mean age at presentation was significantly younger in the more recent decades (3.4 versus 5.4 weeks for 1995 versus 1975, respectively). Electrolyte abnormalities were absent in most infants (88 percent) in all groups. How much of a role the advances in diagnostic imaging during this time have played in earlier detection, as opposed to a generally increased awareness by clinicians, is controversial. One study found that the increased use of diagnostic imaging between the periods of 1974 to 1977 and 1988 to 1991 did not necessarily lead to earlier diagnosis or shorter pre- and post-operative hospital stay but did seem to correlate with a reduced physicians' ability to palpate the pyloric "olive" (from 87 percent to 49 percent in the two different time periods) [ 19].
Atypical presentation — In infants with 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 [ 23]. In infants with gastrointestinal anomalies, post-operative vomiting may initially be attributed to adhesions or obstruction at an anastomotic site [ 23].
In premature infants with IHPS vomiting may be less forceful, voracious appetite and exaggerated gastric peristalsis may be lacking, and ultrasonographic criteria for diagnosis may not apply [ 23-26]. In hospitalized premature infants, nonprojectile vomiting, weight loss, and lethargy may initially be attributed to sepsis; negative cultures, rapid improvement with intravenous fluids, and metabolic alkalosis (rather than acidosis) in such infants should prompt consideration of IHPS [ 23].
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 epigastric mass since [ 23,24].
Clinical associations — Numerous clinical associations have been described with IHPS.

Hyperbilirubinemia is one of the most frequent clinical associations of IHPS (occurring in 14 percent of cases in one series [ 27]). This combination of findings is known as the icteropyloric syndrome. Unconjugated hyperbilirubinemia is more common than conjugated hyperbilirubinemia, and tends to resolve soon after surgical intervention [ 28]. Unconjugated hyperbilirubinemia in infants with IHPS may be related to decreased levels of hepatic glucuronyl transferase [ 29-31] or mutations in the bilirubin uridine diphosphate glucuronosyl transferase gene (UGT1A1*28), which causes Gilbert syndrome [ 27]. Other etiologies for hyperbilirubinemia should be considered in patients with conjugated hyperbilirubinemia, as was described in a patient who had concomitant alpha-1-antitrypsin deficiency [ 32
Midgut malrotation has been described in up to 5 percent of infants with IHPS [ 33]. An association with malrotation, congenital short bowel, and IHPS also has been reported but is much less common [ 34-37].
An absent or hypoplastic mandibular frenulum, as well as joint hypermobility, has been observed [ 38,39].
Other clinical diagnoses described less frequently include eosinophilic gastroenteritis [ 40], gastric ulcer [ 41], hiatal hernia [ 42], diaphragmatic hernia [ 43], congenital heart disease [ 44], propionic acidemia [ 45], congenital nephrotic syndrome [ 46], and congenital hypothyroidism [ 47]. At least one case of congenital pyloric stenosis has been diagnosed in an infant with an intrauterine history of polyhydramnios [ 48]. 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 [ 49]. The symptoms resolved after implementation of a fat-restricted diet.
DIAGNOSIS — Diagnosis of IHPS is straightforward when the "olive" is palpable; otherwise, it can be difficult to differentiate from gastroesophageal reflux (GER), especially in the early stages. As mentioned above, the "olive" is most easily felt immediately after emesis. 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. An examination performed while the infant is quiet is optimal.
When the "olive" and/or peristaltic waves cannot be detected, diagnosis can be confirmed by an ultrasound or upper gastrointestinal (UGI) contrast study [ 9,50,51]. The decision regarding which of these modalities should be the first choice for diagnosis of IHPS varies from center to center and from case to case, depending upon numerous variables, including the likelihood of diagnosis, the level of skill of the ultrasonographer, and the relative cost of the procedures ( show table 1).
Ultrasonography — As mentioned above, the accuracy of ultrasound is operator-dependent, and diagnostic criteria vary from center to center. The measurements most commonly used are pyloric muscle thickness (PMT) ( show figure 1), pyloric muscle length (PML), and pyloric diameter (PD). Published criteria have ranged from 3 to 4 mm for PMT, 15 to 19 mm for PML, and 10 to 14 mm for PD [ 52-54]. These measurements may not be applicable in premature infants [ 24-26]. Each of these measurements has, on its own, at some point been touted as the most reliable of the three [ 55-58]. However, all three measurements typically are used together in practice.
Other less frequently proposed ultrasonographic criteria for the diagnosis of IHPS have included pyloric volume (PV) and pyloric ratio (PR). The PV has been defined as equal to 0.25 pi x PD(2) x PML; infants with IHPS were found to have a significantly higher value than were those without IHPS [ 59]. The PR is described as PMT/PD and is significantly higher in infants with IHPS, with a sensitivity and specificity of 96 and 94 percent, respectively [ 60].
Ultrasonographic diagnosis of IHPS has potential pitfalls. The ultrasonographic findings of pylorospasm may, at least transiently, mimic those of IHPS [ 61]. The ultrasonographer also must be aware of potential false-positive readings caused by a fluid-filled duodenal bulb and gastric antrum and false-negative interpretation resulting from poor visualization caused by overlying bowel gas [ 62]. A posterior sonographic view may be helpful in the latter situation [ 63].
Barium studies — The classic signs on UGI are an elongated pyloric canal ( show figure 2), the "double-track" sign (two thin tracts of barium along the pyloric canal created by compressed pyloric mucosa), and the "shoulder" sign created by the prepyloric bulge of barium [ 64-66]. The main disadvantage of an UGI is radiation exposure.
Upper endoscopy — Upper endoscopy usually is reserved for patients in whom other imaging modalities are inconclusive [ 67].
Other methods[size=18] — Other potentially useful clinical assessments include fasted gastric volume and serum acid-base determinations. In one study, IHPS was present in nearly 92 percent of infants with a nasogastric aspirate of 10 mL or more after three to four hours of fasting [ 68]. In contrast, GER was diagnosed in nearly 86 percent of those with aspirates of less than 10 mL. Another 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 [ 69].
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