Pyloric Stenosis

• 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)