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, potentially leading to dehydration and weight loss.

The radiologist plays a central role in diagnosing this condition. The treatment is surgical.

Structure

There are four main regions in the stomach: the cardia, fundus, body, and pylorus (image). The cardia (or cardiac region) is the point where the esophagus connects to the stomach and through which food passes into the stomach. Located inferior to the diaphragm, above and to the left of the cardia, is the dome-shaped fundus. Below the fundus is the body, the main part of the stomach. The funnel-shaped pylorus connects the stomach to the duodenum. The wider end of the funnel, the pyloric antrum, connects to the body of the stomach. The narrower end is called the pyloric canal, which connects to the duodenum. The smooth muscle pyloric sphincter is located at this latter point of connection and controls stomach emptying. In the absence of food, the stomach deflates inward, and its mucosa and submucosa fall into a large fold called a ruga.

The convex lateral surface of the stomach is called the greater curvature; the concave medial border is the lesser curvature. The stomach is held in place by the lesser omentum, which extends from the liver to the lesser curvature, and the greater omentum, which runs from the greater curvature to the posterior abdominal wall.

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 to 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.

Epidemiology

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 to 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.

History and Physical

Infants with pyloric stenosis classically present with projectile, non bilious 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, non-tender, 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 signs 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 the absence of gas in the colon secondary to gastric obstruction. Caterpillar sign may be present, which is a radiological finding that shows a dilated stomach appearance 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.

Differential Diagnosis

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. An abdominal CT scan will show an inverted relationship between the superior mesenteric artery and the 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.

Prognosis

The prognosis is excellent when diagnosed early. Surgery is curative. There is minimal mortality.

Complications

A delayed diagnosis can lead to dehydration and hypovolemic shock.

Postoperative and Rehabilitation Care

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.

Consultations

Consultation with a neonatal surgeon should begin as soon as the radiologist makes the diagnosis.

Deterrence and Patient Education

Health care professionals should educate parents about the strong family risk of pyloric stenosis. There is a 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.

Pearls and Other Issues

There are other causes of vomiting in infancy, such as midgut volvulus, a web of the gastric antrum, duodenal web, annular pancreas.

There can be a degree of pylorospasm in infants, which is responsible for some delay in gastric emptying. In pylorospasm cases, the ultrasound shows a normal thickness of the pylorus muscle and a normal length of the pylorus channel.

Enhancing Healthcare Team Outcomes

The prompt diagnosis and treatment of infants with pyloric stenosis require cooperation among several in-hospital medical professions, operating as an interprofessional healthcare team. 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. A pharmacist can help with electrolytes and other medication orders, and nursing will be administering these and provide an important backstop to prevent errors and report on patient response. This interprofessional approach will lead to improved patient outcomes.

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.