14-07: Hypertrophic Pyloric Stenosis

Clinical Summary

Hypertrophic pyloric stenosis (HPS) is characterized by progressive postprandial, nonbilious vomiting that steadily increases in frequency and amount due to hypertrophy of the pyloric musculature and edema of the pyloric canal, producing gastric outlet obstruction. It is usually diagnosed in infants from birth to 5 months, most commonly at 2 to 8 weeks of life. The vomiting may become forceful and is then described as projectile (although this pattern is not always present). There is a familial tendency, and white males (especially firstborn) are more frequently affected. During the physical examination, peristaltic waves may be observed traveling from the left upper to right upper quadrants. The hypertrophy of the antral and pyloric musculature produces the “olive” to palpation (best palpated in the epigastrium or right upper quadrant after emesis, following feeding, or after emptying the stomach with a nasogastric tube). As a result of persistent vomiting, hypochloremic, hypokalemic metabolic alkalosis with varying degrees of dehydration and failure to thrive may occur when the diagnosis is not made early in the course.

The finding of a pyloric “olive” on palpation of the abdomen is pathognomonic but has largely been supplanted by transabdominal ultrasound. Diagnosis is confirmed by a pyloric muscle thickness, pyloric muscle channel length, and pyloric diameter of 3 mm, 15 mm, and 10 mm, respectively. The differential diagnosis includes intestinal obstruction or atresia, malrotation with volvulus, hiatal hernia, gastroenteritis, adrenogenital syndrome, increased intracranial pressure, esophagitis, sepsis, gastroesophageal reflux, and poor feeding technique.

Management and Disposition

Treatment includes correction of electrolyte imbalances and dehydration, as well as surgical consultation for curative Ramstedt pyloromyotomy. Failure to correct metabolic alkalosis prior to surgery can increase the risk of postoperative apnea.

Pearls

1. HPS is the most common cause of metabolic alkalosis in infancy.

2. Serial examinations and observation of the child after oral fluid challenges for persistent projectile vomiting may aid in making the diagnosis.

3. Clinical manifestations of pyloric stenosis begin at a mean age of 3 weeks after birth.

4. Pyloric ultrasonography is the diagnostic study of choice.

5. Less than 2% of infants with HPS have bilious vomiting. Some may have hematemesis.