82 HYPERTROPHIC PYLORIC STENOSIS
Denis D. Bensard M.D.

1. What is pyloric stenosis?

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Hypertrophic pyloric stenosis (HPS) is idiopathic thickening and elongation of the pylorus that produces gastric outlet obstruction. HPS is the most common surgical cause of nonbilious vomiting in infants. Offspring of an affected parent have an increased incidence of HPS (10%); the highest rate (20%) occurs in boys born to affected mothers.

2. Describe the typical presentation of HPS.

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The typical presentation is a healthy infant who initially fed normally but who presents at age 2-6 weeks with a history of “projectile” vomiting. The emesis is nonbilious. After vomiting, the infant appears hungry and will refeed immediately. With time, the infant becomes dehydrated and, if allowed to progress, malnutrition follows.

3. What are the physical findings?

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Affected infants suffer some degree of dehydration. The abdomen is nondistended and soft. A palpable pyloric tumor, known as the “olive,” confirms the diagnosis. An olive is palpable in 50% of patients. Associated findings are rare, but mild jaundice occurs in 5% of infants because of reduced glucuronyl transferase activity.

4. How is the diagnosis confirmed?

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Ultrasonographic criteria include pyloric diameter > 1.4 cm, wall width > 4 mm, and pyloric channel length > 1.6 cm. Alternatively, a barium upper gastrointestinal (UGI) examination may be used to confirm the diagnosis (gastric outlet obstruction, pyloric channel narrowing). Current analyses suggest that UGI is the most cost-effective initial radiologic diagnostic test because, unlike ultrasound, alternative causes of nonbilious vomiting (e.g., gastroesophageal reflux, malrotation, duodenal stenosis) can be identified.

5. Describe the likely electrolyte abnormalities.

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Electrolyte levels are often normal, but long-standing vomiting will eventually result in hypokalemic, hypochloremic metabolic alkalosis because of the loss of gastric acid (HCl). Earlier consideration of the diagnosis has led to a significant reduction in this classic electrolyte abnormality at presentation. Dehydration is corrected with either 0.9% NaCl or, in less severe cases, 0.5% NaCl with 30 mEq/L KCl. After dehydration and electrolytes are corrected, pyloromyotomy is performed.

6. What procedure is recommended for the correction of HPS?

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The Fredet-Ramstedt pyloromyotomy is recommended. A superficial incision is made longitudinally over the pyloric muscle in an avascular area, and the muscle fibers are fractured to expose the underlying mucosa. At the conclusion of the pyloromyotomy, the gastric mucosa should bulge upward into the cleft, and the pyloric muscle walls should move independently of one another. Air is injected into the stomach via the nasogastric tube to identify inadvertent mucosal perforation. Pyloromyotomy may be performed either via a transverse incision in the right upper quadrant (i.e., an open procedure) or via three small (3-mm) incisions in the epigastrium (i.e., a laparoscopic procedure). The results of open and laparoscopic pyloromyotomy appear equivalent.

7. What should be done if a perforation is identified?

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The mucosa should be closed with several fine sutures and covered with an omental patch. If the mucosal injury is too extensive, the myotomy should be closed with sutures and a second, parallel myotomy should be made at 45-180° from the original myotomy.

8. When can postoperative feeding begin?

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Small-volume feedings are started after the infant has recovered from anesthesia (2-3 hours) and advanced to goal. Small amounts of vomiting are common (20%), but most infants achieve full feeds within 24 hours postoperatively. Incomplete pyloromyotomy is uncommon (< 1%) and is not considered unless symptoms of gastric outlet obstruction persist for 7-10 days after surgery.

9. Describe several hypotheses about the pathogenesis of HPS.

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Recent studies of the abnormal pyloric complex demonstrate improper innervation of pyloric smooth muscle, excessive contraction of circular pyloric smooth muscle (decreased nitric oxide synthase), increased extracellular matrix proteins (collagen), and increased expression or local synthesis of growth hormones (i.e., insulin-like growth factor-1, transforming growth factor beta-1, platelet derived growth factor).

References
BIBLIOGRAPHY
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