hypertrophic pyloric stenosis (HPS).
HPS, which is the most common gastrointestinal surgical disease of infancy in the United States, manifests most commonly during the second to sixth weeks of life, with a peak incidence at 3 weeks of age and with rare presentation after the age of 3 months. The major symptom is progressive nonbilious vomiting, which starts as simple regurgitation and progresses to projectile vomiting. This progressive vomiting leads to dehydration and hypochloremic metabolic alkalosis and weight loss. The condition is more common in boys. A palpable “olive” representing the thickened pylorus muscle is present in the right upper quadrant approximately 80% of the time if the infant can be examined in a calm manner (with decreased stomach distention).
If the “olive” cannot be palpated, how can HPS be diagnosed with imaging studies?
The evaluation can begin with a supine or prone radiograph of the abdomen, which can exclude other diagnoses that could be causing similar obstructive symptoms. The radiograph may also reveal a markedly dilated stomach, a soft tissue mass projecting into the gastric antrum, and a paucity of gas in the distal bowel. The suspicion of pyloric stenosis can be confirmed with either US or fluoroscopy. US is the imaging test of choice because it directly visualizes the hypertrophied pylorus muscle without utilizing radiation ( Figure 87-4 ), whereas a UGI examination infers the presence of pyloric stenosis indirectly. With US, the pyloric muscle is seen as a hypoechoic structure greater than 3.5 to 4.0 mm in thickness, surrounding an echogenic compressed pyloric channel. Although less sensitive, the pyloric channel length is another measurement used to make the diagnosis. A length greater than 17 mm is considered as diagnostic for HPS.