Rachel Adams Greenup and Casey M. Calkins
EPIDEMIOLOGY
Infantile hypertrophic pyloric stenosis (IHPS) remains the most common surgical cause of nonbilious vomiting in infants.1 The incidence of pyloric stenosis ranges from 1 per 200 to 1 per 750 live births.
PATHOPHYSIOLOGY AND GENETICS
The pyloric muscle appears to hypertrophy after birth, leading to gastric outlet obstruction. Proposed theories to explain the pathogenesis of infantile hypertrophic pyloric stenosis (IHPS) include decreased nitric oxide synthase production, altered enteric innervation, a lack of interstitial cells of Cajal, various infectious and environmental agents, hypergastrinemia, increased synthesis of epidermal growth factor, and congenital redundancy of the pyloric mucosa.2,3 Certain pharmacologic agents are known to increase the risk of IHPS in the newborn, including prostaglandin E2 infusion or erythromycin administration.4,5
Mode of inheritance is polygenic and modified by sex, with the incidence being 4 to 6 times higher in boys. Although it is believed to be more common in first-born males, birth order seems to be less influential than a smaller family size and higher socioeconomic status.6 The incidence of IHPS is twofold to threefold higher in African Americans than in those of European ancestry and it is rare in Asians. Recently, a genomewide association demonstrated linkage of IHPS with 2 loci on chromosomes 11q14-q22 and Xq23 that each harbor functional candidate genes that are members of the canonical transient receptor potential family of ion channels and have a potential role in smooth-muscle control and hypertrophy.7
CLINICAL FEATURES AND DIFFERENTIAL DIAGNOSIS
The typical age of presentation of IHPS is between 3 to 8 weeks old. Patients present with postprandial, forceful, nonbilious emesis, often referred to as projectile. The infant remains hungry and eager to feed after vomiting. When diagnosis is delayed, prolonged vomiting may lead to dehydration, weight loss, and development of a hypochloremic hypokalemic alkalosis. Additionally, fewer than 5% of patients develop an unconjugated hyperbilirubinemia thought to result from inadequate glucose absorption and an inability to maintain glucuronyl transferase activity.
FIGURE 398-1. Hypertrophic pyloric stenosis. Ultrasonographic diagnosis shows elongated and thickened pyloric muscle (bracketed between markers).
DIAGNOSTIC EVALUATION
The diagnosis of pyloric stenosis is best made by careful physical examination in an infant with a typical history. Observation of visible peristalsis, projectile vomiting, and palpation of a mobile pyloric mass (the “olive”) is pathognomonic. This mass is palpable to an experienced examiner in 80% to 90% of cases,8 but may be difficult to appreciate in the face of a dilated stomach or irritable infant. Gastric decompression and a quiet baby (giving the infant a dextrose-coated pacifier) may aid in examination. If the diagnosis is not clearly evident on the physical examination, ultrasonography is useful to demonstrate the thickened and lengthened pyloric muscle (Fig. 398-1). Ultrasound is both specific and sensitive, with an accuracy of close to 100% in the hands of skilled radiographers.9 A pyloric channel with thickness and length greater than 3 mm and 2 cm, respectively, has been diagnostic of pyloric stenosis.10 Upper GI contrast studies provide the most definitive method for diagnosis, with characteristic findings of elongation and narrowing of the pyloric canal and partial blockage of the canal by thickened mucosa creating a double track of contrast, or a “string-sign.” Contrast studies can also be helpful in allowing evaluation of other causes of vomiting in cases where the diagnosis of pyloric stenosis is less clear. Rarely, upper endoscopy may be useful to clarify the diagnosis in equivocal cases, revealing antral fold hypertrophy or a pyloric mass.
TREATMENT
Since many of these infants present with dehydration and electrolyte abnormalities, appropriate fluid/electrolyte resuscitation remains the priority before initiation of diagnostic or therapeutic procedures. The infant should not be fed. Placement of a nasogastric tube is unnecessary. Alkalosis and hypokalemia must be corrected before the definitive surgery, which is nonemergent. Medical therapy with the chronic administration of atropine has been reported and might be preferable in locales where surgical risk is increased11,12; however, surgical therapy provides safe and effective treatment, with prompt relief of symptoms. Pyloromyotomy remains the gold standard for treatment.
The pyloromyotomy is performed through a longitudinal incision on the anterior surface of the pylorus, dividing the hypertrophied muscle. The open Fredet-Ramstedt pyloromyotomy has been modified by many centers through approaching the pyloromyotomy laparoscopically. There is ample evidence that both procedures are safe and effective, though recovery from a minimally invasive approach may be shorter and less painful, while affording an improved cosmetic result.1,13 The operative technique chosen depends on infant size, status of umbilical healing, and surgeon preference.
PROGNOSIS
Pyloromyotomy is curative with an incidence of recurrence of less than 1%. Postoperative vomiting occurs in as many as 50% of infants initially, but resolves in most within 24 hours. Full oral feedings typically are realized within 24 to 36 hours following surgery. The pyloric muscle regresses to a normal thickness within 12 weeks following pyloromyotomy, and follow-up studies are not routinely indicated in the otherwise thriving infant.14