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Hypertrophic Pyloric Stenosis

by William J. Cochran, MD

Hypertrophic pyloric stenosis is blockage of the passage out of the stomach due to thickening (hypertrophy) of the muscle at the junction between the stomach and the intestines.

  • The thickened muscle creates a partial blockage (obstruction) that interferes with the passage of stomach contents into the small intestine.

  • Infants feed well but vomit forcefully (projectile vomiting) shortly after eating and can become dehydrated and undernourished.

  • The diagnosis is based on results of an abdominal ultrasound.

  • Typically the problem is corrected by fluids given by vein (intravenously) and by minor surgery.

The pylorus is the muscular sphincter located where the stomach joins the first part of the small intestine (duodenum). Normally, the pylorus contracts to keep food in the stomach for digestion and relaxes to let the food out into the intestine. For reasons that doctors do not fully understand, the pylorus becomes thickened and sometimes closes off, blocking material from leaving the stomach. This blockage usually occurs in the first month or two of life and is much more common among boys, especially first-born boys. Rarely, some older children have pyloric obstruction caused by swelling due to peptic ulcers or an uncommon disorder similar to a food allergy (such as eosinophilic gastroenteritis).

Symptoms and Diagnosis

Infants with pyloric stenosis are hungry and feed well but vomit forcefully (projectile vomiting) shortly after eating. Some infants vomit so much that they become dehydrated and undernourished. Until dehydration is severe, or infants become significantly undernourished, they otherwise appear well, unlike those with vomiting caused by other disorders. After several days, infants become progressively dehydrated and lose weight. Some infants have a yellowish discoloration of the skin and the whites of the eyes (jaundice) at this point.

The doctor may be able to feel a small lump (about the size of an olive) in the infant’s abdomen (the enlarged pylorus). Most commonly, the doctor does abdominal ultrasonography to confirm the diagnosis.


Doctors give infants fluids by vein to treat the dehydration and correct any electrolyte imbalance. Then, a surgeon cuts the thickened muscle to relieve the blockage, allowing formula or breast milk to enter the small intestine more readily. This surgery is relatively minor, and most infants can eat within a day of the procedure.

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