Hypertrophic Pyloric Stenosis

Hypertrophic pyloric stenosis (HPS) results from idiopathic hypertrophy and hyperplasia of circular muscle fibers of the pylorus with proximal extension into the gastric antrum. It is technically an acquired rather than congenital condition. The US incidence is 3:1,000 live births. Males are more commonly affected than females by a ratio of 4:1. There is a bimodal distribution for age of presentation. Treatment is surgical by pyloromyotomy.

Infantile Form:

Hypertrophy of the pyloric sphincter results in projectile nonbilious vomiting between the second and sixth weeks of life. Physical exam may reveal a palpable olive-shaped mass representing the hypertrophied pylorus. In the absence of this physical exam finding radiographic evaluation is indicated. Ultrasonography is the imaging modality of choice, followed by an UGIS if US findings are equivocal.

US Findings:

• Pyloric muscle wall thickness > 4mm

• Pyloric canal > 14mm in longitudinal view

• Delayed or absent gastric emptying into the duodenum

• Exaggerated peristaltic waves

UGIS Findings: (See Pediatric Imaging for examples.)

• Elongation and narrowing of the pyloric canal (2-4 cm in length)

• String Sign: Passage of small contrast through the narrowed pyloric channel

• Crowding of mucosal folds in pyloric channel producing a double or triple track sign

• Kirklin or "Mushroom" Sign: Indentation of the duodenal bulb base around the hypertrophied pylorus; also referred to as "shouldering"