The cause of the hypertrophied pylorus muscle is unknown, but it is usually not present at birth. Mean onset of symptoms is 2-3 weeks of life, but range can be birth to 5 months with a 4:1 male to female occurrence.
Clasic presentation is projectile, nonbilious vomiting of last feed which may be immediate or hours later.
Pyloric Stenosis is the most common reason for abdominal surgery in the first 6 months of life.
Textbook lab abnormality is a Hypochloremic hypokalemic metabolic alkalosis but this is a later finding and can not be used to rule out the diagnosis.
Ultrasonography has become the standard imaging technique for diagnosis. It is reliable, highly sensitive, highly specific, and easily performed.
Muscle wall thickness 3 mm or greater and pyloric channel length 14 mm or greater are considered abnormal in infants younger than 30 days.
DDX includes : Normal Regurgitation (all babies do it!!!), GERD, Milk Intorerance, Obstruction (antral webs, volvulus,intussusception)