Hypertrophic pyloric stenosis is the most common cause of metabolic alkalosis in infancy. The incidence of pyloric stenosis ranges from 1 in 250 to 1,000, depending on geographic location, and is reportedly on the rise. Boys are affected four to eight times more often than girls,and there is a Caucasian predilection. In addition, sometimes there is a clustering in families. Pyloric stenosis is the most common reason for abdominal surgery in the first 6 months of life.

Although the precise etiology of pyloric stenosis remains unknown,there is some evidence that it may be an acquired condition, rather than a congenital disorder, as previously thought. In this condition, gastric outlet obstruction results from hypertrophy of the pyloric muscle,edema of the pyloric canal, and spasm of the antropyloric muscle,which leads to vomiting,dehydration, and metabolic alkalosis.

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

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