Clinical Presentation

A 5-week-old boy presents to the emergency department with a 4-day history of nonbilious projectile vomiting.

Figure 65A

Radiologic Findings

Diagnosis

Hypertrophic pyloric stenosis (HPS)

Differential Diagnosis

• Pylorospasm
  
• Other mechanical causes of gastric outlet obstruction (e.g., atresias/webs, prostaglandin-induced foveolar hyperplasia, eosinophilic gastroenteritis, extrinsic mass lesions, annular pancreas)
  
• Gastroesophageal reflux
  
• Metabolic and infectious causes of vomiting (clinical findings)

Discussion

Background

HPS is an acquired hypertrophy of the circular muscle of the pylorus, causing progressive gastric outlet obstruction, It occurs with an incidence of ~3 per 1000 live births. There is an increased incidence in boys (male:female 4:1), first-born children, and Caucasian race. Some cases show a strong familial tendency.

Etiology

The etiology remains largely unknown, although abnormal innervation to the circular muscle has been implicated.

Clinical Findings

Classically, infants present between 2 and 6 weeks of life with projectile nonbilious vomiting occurring 10 to 20 minutes after feeding. Occasional cases as early as the first week of life and as late as 5 months have been described. Infants fail to thrive and may become dehydrated. The classic metabolic abnormality of hypokalemic hypochloremic alkalosis is now rare. On clinical examination, gastric peristaltic activity may be seen and a palpable small mass, the “olive,” may be felt in the right upper quadrant, although earlier diagnosis has reduced the incidence of this finding over the past 2 decades.

Pathology

• A pale fusiform muscle mass is seen macroscopically with a clear transition to normal gut wall distally.
  
• The muscle mass comprises mainly circular muscle fibers, but all layers are involved.
  
• Secondary mucosal changes of edema or ulceration can occur in long-standing cases.

Imaging Findings

ULTRASOUND