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 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 (called stenosis), blocking material from leaving the stomach. This blockage usually occurs in the first month or two of life.
Risk factors include
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).
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. After several days to weeks, 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 may do blood tests to evaluate children for dehydration and an electrolyte imbalance (metabolic alkalosis) resulting from severe vomiting.
Doctors give infants fluids by vein (intravenously) 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 (called pyloromyotomy) is relatively minor, and most infants can eat within a day of the procedure.