History: 3 week old baby boy with vomiting. 

This is a classic case of pyloric stenosis, which is defined as idiopathic hypertrophy of the muscle that makes up the sphincter between the stomach and the first part of the duodenum, called the pylorus. Diagnostic features of pyloric stenosis on ultrasound includes a single wall thickness of the pylorus of more than 3 mm, a pyloric channel of greater than 16 mm, or a pyloric diameter on cross section of more than 15 mm.

Take a look at the image above again. The echogenic layer in the pyloric channel is the mucosal layer, and is not measured when looking at wall thickness.

Ultrasound is the exam of choice when suspecting pyloric stenosis in a baby with projectile vomiting. The best technique includes lying the patient on their right side and administering a glucose water solution to stimulate gastric contractions against the pylorus.

Pyloric stenosis is most commonly seen in infants from 2 – 12 weeks old, and is more common in males than females, with a 4:1 ratio. The classic “palpable olive” on physical exam is 97% specific. A useful article on diagnosing pyloric stenosis in the absence of a palpable olive can be found here.

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