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Pyloric stenosis is a condition in which a baby's pylorus (the connection between the stomach and the first part of the small intestine) gradually swells and thickens. This interferes with food entering the intestine and causes the baby to vomit most or all of his or her feedings.

To treat pyloric stenosis, a surgeon cuts the ring of muscle (sphincter) in the pylorus. This widens the channel between the stomach and the intestine. Pyloric stenosis does not usually occur again after a baby has been treated.