Hypertrophic pyloric stenosis (HPS) is a narrowing of the stomach's exit due to overgrowth of muscle.  This occurs most often in babies that are about 1 to 3 months of age.  HPS causes worsening vomiting with feeds that can lead to severe dehydration and starvation if not treated with surgery.

 

What causes hypertrophic pyloric stenosis (HPS)?

HPS is caused by overgrowth of the muscle that controls the opening and closing of the stomach's exit to the small intestines.  Why this happens... nobody knows, but it seems to happen after birth and gets progressively worse within several weeks.  First born males are more likely than other infants to develop HPS (for unknown reasons).

What are the symptoms of HPS?

Vomiting is the key feature of HPS.  Most often the vomiting is wrongly considered to be normal baby spit-ups until the vomiting happens with every feed and becomes "projectile."  Normal spit-ups usually dribble down the chin of a baby and is only a small portion of the milk meal.  Projectile vomiting can be a large amount of milk that sprays far enough to hit the floor, wall or caregiver.  After vomiting, the infant is hungry and wants to eat again.  As the vomiting continues, the infant may lose weight, become dehydrated and lose electrolytes.

How is HPS diagnosed?

The best test for HPS is an ultrasound.  In some cases, a physician can feel the overgrown muscle with a physical exam.  This "mass" is about 2 cm long and can be felt above and to the right of the belly button.  Blood tests can be helpful in making the diagnosis (the electrolyte panel will show a low blood acid and chloride level) and to determine if dehydration is severe.  Often the history provided by the family is enough to justify getting an ultrasound to confirm the diagnosis.

How is HPS treated?

Dehydration and electrolyte imbalance should be corrected with intravenous fluids.

HPS should be corrected by surgery.  The procedure is called a pyloromyotomy and involves cutting the muscle that surrounds the exit of the stomach (the pylorus).  The pylorus has an outer layer of muscle that acts like a tight rubber band.  Once this tight band of muscle is released, the infant can usually feed within 12 to 24 hours after surgery.

Will HPS come back after surgery?

No.  Surgery cures HPS forever.  If vomiting continues, then either the surgery did not completely release the obstruction or there is another cause of the vomiting.

Can HPS be prevented?

The cause of HPS is unknown and there is no known way to reduce the risk of HPS.