Pyloric stenosis, also known as infantile hypertrophic pyloric stenosis (IHPS), is an uncommon condition in infants characterized by abnormal thickening of the pylorus muscles in the stomach leading to gastric outlet obstruction. Clinically infants are well at birth. Then, at 3 to 6 weeks of age, the infants present with "projectile" vomiting which can lead to dehydration and weight loss.
The radiologist plays a central role in diagnosing this condition. The treatment is surgical.
The exact etiology of infantile hypertrophic pyloric stenosis is unknown. Some studies have shown that young infants treated with macrolide antibiotics had an increased incidence of infantile hypertrophic pyloric stenosis. Postnatal exposure of erythromycin has also been associated with an increased risk for the development of pyloric stenosis. Other risk factors include bottle feeding, preterm birth, cesarean section delivery, and first-born infants (30% to 40% of cases). If the mother was a heavy smoker during pregnancy, the risk of hypertrophic pyloric stenosis could increase by 1.5. to 2.0 fold.
The incidence of pyloric stenosis is 2 to 5 in 1000 live births per year. It is more common in males; there is a male to female ratio of 4:1. There is a familial link, but the hereditary pattern is polygenic. Pyloric stenosis is more common in the white population. It is less commonly seen in Indian, Asian, and Black populations.
The incidence is 2.4 per 1000 in whites, 1.8 in Hispanics, 0.7 in blacks, and 0.6 in Asians.
The hallmark of pyloric stenosis is marked hypertrophy and hyperplasia of both the circular and longitudinal muscular layers of the pylorus. This thickening leads to the narrowing of the lumen of the gastric antrum. The pyloric canal becomes lengthened. The muscles of the pylorus become thickened. The mucosa becomes edematous and thickened. When severe, the stomach becomes dilated secondary to gastric outlet obstruction. This obstruction induces immediately postprandial, nonbilious, projectile emesis.
Infants with pyloric stenosis classically present with projectile, nonbilious vomiting. Vomiting may be intermittent or occur after each feeding. Emesis should not be bilious. In about 60% to 80% of the infants with pyloric stenosis, a firm, nontender, hard pylorus measuring 1 to 2 cm in diameter, classically described as an "olive," may be present in the right upper quadrant. The clinician may also observe reverse peristaltic waves.
Infants may show dehydration. Signs of dehydration in infants are: depressed fontanelles, dry mucous membranes, decreased tearing, poor skin turgor, and lethargy.
The classic electrolyte imbalance of pyloric stenosis is hypochloremic, hypokalemic metabolic alkalosis. The diagnosis of pyloric stenosis is being made earlier because of earlier use of sonography so that those laboratory abnormalities are now present in less than 50% of cases. Dehydration may cause either hypernatremia or hyponatremia; both can lead to prerenal renal failure. Elevated unconjugated bilirubin levels may be present.
Infants with severe vomiting caused by pyloric stenosis can develop profound hypochloremia and hypokalemia. The classic biochemical abnormality in hypertrophic pyloric stenosis is hypochloremic, hypokalemic metabolic alkalosis.
Ultrasonography has become the standard imaging technique for diagnosing hypertrophic pyloric stenosis. It is reliable, highly sensitive, highly specific, and easily performed. An experienced ultrasonographer is necessary to diagnose pyloric stenosis. A novice sonographer may have trouble locating the pylorus. Pyloric wall thickness 3 mm or greater and pyloric channel length 15 mm or greater are considered abnormal and indicate pyloric stenosis. Ultrasound findings also include target sign and lack of gastric emptying.
Barium upper can help to diagnose pyloric stenosis when ultrasonography is not diagnostic but is rarely necessary. It should demonstrate an elongated pylorus and can show marked delayed gastric emptying. Findings may include string sign, double-track sign, or beak sign.
Sometimes, upper endoscopy, performed by a pediatric gastroenterologist, can be used as an additional diagnostic tool in rare, select cases when the other imaging tests are nondiagnostic or when the infant presents with atypical clinical features.
Abdominal x-ray lacks sensitivity and specificity significantly. Findings may include large stomach gas with absence of gas in colon secondary to gastric obstruction. Caterpillar sign may be present, which is a radiological finding that shows the appearance of the dilated stomach secondary to hypertrophied pylorus gastric contractions.
First, medical treatment is necessary and usually consists of rehydration and correction of electrolyte imbalances. If no or mild signs of dehydration are evident, 5% dextrose with 0.25% NaCl and 2 meq KCl per 100 mL is given. If moderate or severe, recommend higher IVF NaCl concentrations. Bicarbonate levels should be corrected and monitored, given the impact on potential hypoventilation. NG tube should be considered.
Once the infant is rehydrated, surgery is the next step.
Treatment is surgical and is called pyloromyotomy. In this surgery, the pyloric muscle is divided down to the submucosa. The surgery can be performed open or laparoscopically, depending on the surgeon. The operation is curative and has very low morbidity.
Midgut volvulus is a twisting of malrotated bowel which can present in the first month of life with bilious vomiting. An upper GI series will show a "corkscrew" appearance of the bowel. Abdominal CT scan will show an inverted relationship between the superior mesenteric artery and superior mesenteric vein.
Also in the differential diagnosis are gastroenteritis, acute renal failure, sepsis, hernia, colic, constipation, necrotizing enterocolitis, trauma, toxic megacolon, Hirschsprung disease, testicular torsion, appendicitis, and urinary tract infection.
The prognosis is excellent when diagnosed early. Surgery is curative. There is minimal mortality.
A delayed diagnosis can lead to dehydration and hypovolemic shock.
The only postoperative care is a continuation of intravenous fluids until they tolerate feeding. Feeding can begin 4 to 8 hours after recovery from anesthesia. 
Up to 80% of patients continue to have some milder form of vomiting after surgery. If vomiting persists 5 days postoperatively, they would indicate further radiologic studies such as an upper GI series.
Postoperatively, infants should be observed in the hospital for surgical complications such as incomplete pyloromyotomy, mucosal perforation, and bleeding.
The infants may be discharged home when hydrated and tolerating feedings well.
Consultation with a neonatal surgeon should begin as soon as the diagnosis made by the radiologist.
Health care professionals should educate parents about the strong family risk of pyloric stenosis. There is nearly 200-fold increased risk among identical twins and a 20-fold increase among siblings. So parents should be vigilant in identifying symptoms in their future offspring as early as possible.
There are other causes of vomiting in infancy, such as midgut volvulus, a web of the gastric antrum, duodenal web, annular pancreas.
In infants, there can be a degree of pylorospasm, which is responsible for some delay in gastric emptying. In cases of pylorospasm, the ultrasound shows a normal thickness of the pylorus muscle and a normal length of the pylorus channel.
The prompt diagnosis and treatment of infants with pyloric stenosis require cooperation among several in-hospital medical professions. First, the emergency room physicians must assess the infant and begin intravenous fluids as needed. The emergency physicians request an emergent abdominal ultrasound. The radiologist should provide a prompt diagnosis by doing a stat pediatric ultrasound by a trained sonographer. A surgeon with expertise in neonatal pyloric stenosis surgery must be consulted as soon as the diagnosis is made.
Ultrasound is being used much earlier to aid in the diagnosis, and the classic signs of infantile hypertrophic pyloric stenosis are 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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