Pediatric Pyloric Stenosis

Marked hypertrophy and hyperplasia of the 2 (circular and longitudinal) muscular layers of the pylorus occurs, leading to narrowing of the gastric antrum. The pyloric canal becomes lengthened, and the whole pylorus becomes thickened. The mucosa is usually edematous and thickened. In advanced cases, the stomach becomes markedly dilated in response to near-complete obstruction.

The causes of infantile hypertrophic pyloric stenosis are multifactorial.[2] Both environmental factors and hereditary factors are believed to be contributory. Possible etiologic factors include deficiency of nitric oxide synthase containing neurons, abnormal myenteric plexus innervation, infantile hypergastrinemia, exposure to macrolide antibiotics, lack of exposure to vasoactive intestinal peptide in breast milk, and hypersensitivity to motilin.

A meta-analysis that investigated perinatal factors associated with hypertrophic pyloric stenosis onset and reported that first-born (OR 1.19, 95% CI: 1.07-1.33), cesarean section delivery (OR 1.63, 95% CI: 1.53-1.73), preterm birth (OR 1.37, 95% CI: 1.12-1.67), and bottle-feeding (OR 2.46, 95% CI: 1.76-3.43), were associated with the hypertrophic pyloric stenosis onset with bottle-feeding as the most significant risk factor.[3, 4]

 A cohort study found that treatment of young infants with macrolide antibiotics was strongly associated with infantile hypertrophic pyloric stenosis (IHPS).[5]  A meta-analysis of 9 studies reaffirmed a significant association of postnatal exposure of erythromycin and the development of pyloric stenosis. This association is strongest if the exposure occurred in the first 2 weeks of life, although persists to a lesser degree in children between 2 and 6 weeks of age.[6, 7, 8] Maternal use of macrolides during the first 2 weeks after birth was also associated with an increased risk of IHPS.[5]

Nitric oxide has been demonstrated as a major inhibitory nonadrenergic, noncholinergic neurotransmitter in the GI tract, causing relaxation of smooth muscle of the myenteric plexus upon its release. Impairment of this neuronal nitric oxide synthase (nNOS) synthesis has been implicated in infantile hypertrophic pyloric stenosis, in addition to achalasia, diabetic gastroparesis, and Hirschsprung disease.

Another study reported the possibility that low serum lipids could be a risk factor for IHPS. Further studies are needed to determine the significance of these findings.[9]

Rogers has suggested, that persisting duodenal hyperacidity, due to a high parietal cell mass (PCM) and loss of gastrin control, produces pyloric stenosis from repeated pyloric contraction in response to hyperacidity.[10]

No specific pattern of inheritance exists, although there is likely a genetic component to IHPS development. It is more common in first-born white males of northern European ancestry and occurs more frequently in monozygotic than dizygotic twins. Children of affected parents are also affected at a higher rate (as high as 7%).

A nationwide study of nearly 2 million Danish children born between 1977 and 2008 shows strong evidence for familial aggregation and heritability of pyloric stenosis. Results of the study found a heritability rate of 87% in affected families, lending to the idea that familial aggregation may be explained by shared genes that affect responses to postnatal factors in causing pyloric stenosis.[11]

United States

The incidence of infantile hypertrophic pyloric stenosis is 2-4 per 1000 live births.

Mortality/Morbidity

Death from infantile hypertrophic pyloric stenosis is rare and unexpected. The reported mortality rate is very low and usually results from delays in diagnosis with eventual dehydration and shock.

Race

Infantile hypertrophic pyloric stenosis is more common in whites than Hispanics, blacks, or Asians. The incidence is 2.4 per 1000 live births in whites, 1.8 in Hispanics, 0.7 in blacks, and 0.6 in Asians. It is also less common amongst children of mixed race parents.

Sex

Infantile hypertrophic pyloric stenosis has a male-to-female predominance of 4-5:1, with 30% of patients with infantile hypertrophic pyloric stenosis being first-born males.

Age

The usual age of presentation is approximately 2 – 6 weeks of life. Approximately 95% of infantile hypertrophic pyloric stenosis cases are diagnosed in those aged 3-12 weeks. Infantile hypertrophic pyloric stenosis is rare in premature infants. In addition, premature infants have a delayed diagnosis secondary to low birth weight and atypical presentation.

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• Classically, the infant with pyloric stenosis has nonbilious vomiting or regurgitation, which may become projectile (in as many as 70% of cases), after which the infant is still hungry. ^[12]
• Emesis may be intermittent initially, or occur after each feeding.
• Emesis should not be bilious as the obstruction is proximal to the common bile duct. The emesis may become brown or coffee color due to blood secondary to gastritis or a Mallory-Weiss tear at the gastroesophageal junction.
• As the obstruction becomes more severe, the infant begins to show signs of dehydration and malnutrition, such as poor weight gain, weight loss, marasmus, decreased urinary output, lethargy, and shock.
• The infant may develop jaundice, which is corrected upon correction of the disease.

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• In as many as 60-80% of the infants with infantile hypertrophic pyloric stenosis (IHPS), a firm, nontender, and mobile hard pylorus that is 1-2 cm in diameter, described as an "olive," may be present in the right upper quadrant at the lateral edge of the rectus abdominis muscle. This is best palpated after the infant has vomited and when calm, or when the gastric contents have been removed via nasogastric tube. The palpation of an olive mass has a 99% positive predictive value for IHPS diagnosis. ^[13]
• Clinicians may also observe gastric peristalsis just prior to emesis as the peristaltic waves try to overcome the obstruction.
• Signs of dehydration include depressed fontanelles, dry mucous membranes, decreased tearing, poor skin turgor, and lethargy.
• Due to the widespread early use of ultrasonography to aid in diagnosis, the classic signs of infantile hypertrophic pyloric stenosis are becoming less common. The mean age of presentation is getting significantly younger, and infants are not developing the physical signs or electrolyte abnormalities they were in the past.

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• The etiology of infantile hypertrophic pyloric stenosis is unknown and is probably multifactorial (genetic and environmental factors).

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• Electrolytes, pH, BUN, and creatinine levels should be obtained at the same time as intravenous access in patients with pyloric stenosis.
• Hypochloremic, hypokalemic metabolic alkalosis is the classic electrolyte and acid-base imbalance of pyloric stenosis. This constellation of electrolyte abnormalities is now present in less than 50% of cases given the prompt and timely diagnosis of most infants with pyloric stenosis. However, delayed presentations, or missed cases may lead to persistent emesis. This prolonged vomiting causes progressive loss of fluids rich in hydrochloric acid, which causes the kidneys to retain hydrogen ions in favor of potassium.
• The dehydration may result in hypernatremia or hyponatremia and may result in prerenal renal failure.
• Elevated unconjugated bilirubin levels may be present.

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• If the clinical presentation is typical and an olive is felt, the diagnosis is almost certain. However formal ultrasonography is still recommended to evaluate the pylorus and confirm the diagnosis.
• Ultrasonography is the imaging modality of choice when evaluating a child for infantile hypertrophic pyloric stenosis (IHPS). ^[14] It is both highly sensitive (90-99%) and specific (97-100%) in the hands of a qualified sonographer. The pylorus is viewed in both longitudinal and transverse planes. The sonographic hallmark of infantile hypertrophic pyloric stenosis is the thickened pyloric muscle.
• As many infants present through the emergency department, point of care ultrasonography can be used at the bedside to help the emergency physician image the pylorus. One study by Svitiz et al, found that pediatric emergency physicians had a 100% sensitivity and specificity of identifying pyloric stenosis. ^[15]
• Criteria for making the diagnosis include pyloric muscle wall thickness equal to or greater than 3 mm, and pylorus length greater than 13mm. The entire pyloric diameter may range from 10-14 mm.

Point-of-care ultrasound performed by a pediatric emergency physician accurately identifying the pyloric wall thickness and length that meets criteria for pyloric stenosis diagnosis.

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• Other sonographic signs associated with pyloric stenosis include the ‘antral nipple’ sign, the ‘shoulder’ sign and ‘donut’ sign.

The ‘antral nipple sign’ demonstrated by the arrow, the ‘X’ indicates the ‘shoulder sign’

The ‘donut’ sign demonstrated by the arrow.

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• Infantile hypertrophic pyloric stenosis may be falsely diagnosed in infants who have pylorospasm. Ultrasonography also allows for observation of peristaltic activity, differentiating between pylorospasm and true infantile hypertrophic pyloric stenosis.
• Upper GI imaging (UGI) can help to confirm the diagnosis of infantile hypertrophic pyloric stenosis but is not routinely performed unless ultrasonography is nondiagnostic.
• Although rarely performed now, the upper gastrointestinal study used to be the gold standard. The "shoulder" sign is a collection of barium in the dilated prepyloric antrum and may be seen in the infant with infantile hypertrophic pyloric stenosis. The "double track" sign (ie, 2 thin tracks of barium compressed between thickened pyloric mucosa), once thought to be pathognomonic of infantile hypertrophic pyloric stenosis, has recently been identified in multiple cases of sonographically confirmed pylorospasm and is shown in the image below.

Lateral view from an upper GI study demonstrates the double-track sign.

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• Upper GI endoscopy has been used as an adjunct diagnostic tool in select cases of infantile hypertrophic pyloric stenosis when other imaging tests are inconclusive or when the infant presents with atypical clinical features.

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• As with all pediatric resuscitations, prehospital care in patients with pyloric stenosis should be consistent with pediatric advanced life support (PALS) recommendations for infants who are dehydrated or in shock.
• Immediate treatment requires correction of fluid loss, electrolytes, and acid-base imbalance. Once intravenous access is obtained, the dehydrated infant should receive an initial bolus (20 mL/kg) of crystalloid fluid. The infant should remain nothing by mouth (NPO).

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• Infantile hypertrophic pyloric stenosis (IHPS) may be described as a medical emergency or a medical urgency based on how early in the course the patient presents.
• If significant dehydration has occurred, immediate treatment requires correction of fluid loss, electrolytes, and acid-base imbalance, starting with an initial fluid bolus (20ml/kg) of isotonic crystalloid.
• More than 60% of infants present to the ED with normal electrolyte values and are not significantly dehydrated. These infants should receive 1.5-2 times maintenance intravenous fluid: 5% dextrose in 0.45% normal saline with 20mEq/l of potassium chloride replacement. The infant's fluid status should be continuously reassessed with special attention to acid-base status and urine output.
• A request for pyloric ultrasound should be made for definitive diagnosis of pyloric stenosis.  This is not emergent and may be performed after the patient is stabilized and as an in-patient as well.
• The definitive treatment for infantile hypertrophic pyloric stenosis is corrective surgery, thus once the diagnosis has been confirmed, a pediatric surgeon should be consulted.

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• A surgeon comfortable with neonatal care should be consulted as soon as the diagnosis of infantile hypertrophic pyloric stenosis is entertained.

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• Nonsurgical treatment for infantile hypertrophic pyloric stenosis with atropine sulfate, either intravenous or oral, is an alternative in the rare case that general anesthesia or surgery is contraindicated. ^[25] In a systematic review that identified 10 studies, treatment with atropine had a lower success rate and longer duration of therapy compared to conventional pyloromyotomy. ^[16]
• A recent nationwide review of pyloric stenosis management with atropine in Japan echoed similar findings – they found that surgical intervention has a higher success rates, minimal complications and shorter duration of hospital stay compared to atropine therapy. ^[17]

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• The definitive treatment for infantile hypertrophic pyloric stenosis is corrective surgery.
• The Ramstedt pyloromyotomy is the current procedure of choice, during which the underlying antro-pyloric mass is split leaving the mucosal layer intact.

  • Traditionally, the pyloromyotomy was performed through a right upper quadrant transverse incision. New studies have compared the operative time, cost, and hospital stay associated with the traditional incision, a circumbilical incision (believed to have improved cosmesis), and a laparoscopic procedure.
  • Studies have shown laparoscopic pyloromyotomy to have fewer complications, reduced time to full feeds and hospital length of stay compared to open pyloromyotomy. ^{[18, 19, 24]} However, a meta-analysis of 4 randomized controlled trials comparing laparoscopic pyloromyotomy to open pyloromyotomy found no difference in complication rates, or hospital length of stay between the two groups. It did find a reduction in time to full feeds by 2 hours in the laparoscopic pyloromyotomy group. ^[20]  

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• Atropine has been studied as a potential for conservative management of pyloric stenosis. It is either administered intravenously or orally with the goal of treatment being cessation of projectile vomiting. Success rates vary across studies from 76% to 100% with a mean hospital length of stay of 13 days. ^[16]
• The intravenous dose of atropine for treatment of pyloric stenosis ranges in studies from 0.04 to 0.225mg/kg/day and is given for 1 – 10 days.
• Oral atropine (0.08 – 0.45mg/kg/day) is continued, after IV therapy has been deemed successful, for 3 weeks to 4 months. Predictors of failure are a total of 5 or more projectile vomiting episodes during the first 72 hours of intravenous atropine therapy.
• Side effects of atropine therapy are rare and include mild facial flushing, raised alanine transaminase and tachycardia. ^[16]

The infant with pyloric stenosis should continue to receive intravenous fluid until feeding is resumed. Feeding can be initiated 4-8 hours after recovery from anesthesia, although earlier feeding has been studied. Infants who are fed earlier than 4 hours do not have a worse total clinical outcome; however, they do vomit more frequently and more severely, leading to significant discomfort for the patient and anxiety for the parents.

• As many as 80% of patients continue to regurgitate after surgery; however, patients who continue to vomit 5 days after surgery may warrant further radiologic investigation.
• Patients should be observed for surgical complications (eg, incomplete pyloromyotomy, mucosal perforation, bleeding) and may be discharged home when adequately hydrated and tolerating feedings well.
• A study from the Children's Hospital of Philadelphia showed that a standardized feeding regimen had no advantage over ad libitum feedings. ^[21]

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• Surgery is curative with minimal mortality. ^[22]
• The prognosis is very good, with complete recovery and catch-up growth if detected in a timely fashion.

In the patient that presents with vomiting and has a missed/delayed diagnosis of pyloric stenosis, there is risk of significant dehydration leading to hypovolemic shock.