Findings: There is thickening and elongation of the pyloric muscle. The pyloric muscle measures over 6 mm in thickness and the pyloric channel 18 mm in length. These are both abnormal measurements and are diagnostic for this condition.
Diagnosis: Hypertrophic pyloric stenosis (HPS).
Discussion: Hypertrophic pyloric stenosis (HPS) is a common acquired abnormality due to hypertrophy of the circular muscle of the pylorus and is the most common GI disease of infancy in the United States that requires surgery. Males are affected four times as often as females and in whites the incidence is 1.26 per 1000 and in blacks .48 per 1000. Symptoms include non-bilious vomiting often starting as simple regurgitation progressing to projectile vomiting after most feedings. Less frequent findings are constipation, weight loss, dehydration, hypochloremic alkalosis, jaundice and hemorrhage seen in neonates and infants. Symptoms of HPS occur most commonly during the second to sixth weeks with peak age at presentation being three weeks. HPS rarely presents after 3 months of age. Physical examination may reveal visible gastric peristaltic waves and a palpable pyloric mass (olive). Plain film findings include gastric distention and paucity of distal bowel gas. The etiology of HPS is uncertain.
If the clinical and physical findings are suggestive of HPS then an ultrasound exam is the first study of choice. If there is concern for other causes of obstruction such as malrotation or midgut volvulus an UGI exam should be performed especially if there is bilious vomiting.
Ultrasound evaluation of the anteropyloric region is performed with the infant in the supine and right lateral decubitus position. If there is insufficient gastric fluid in the antrum the infant can be given several ounces of sugar water to better define the pylorus. A normal pyloric muscle diameter is less than 3mm and the normal pyloric channel is less than 18 mm in length. The diagnostic features of HPS are lack of peristalsis in the persistently narrowed pylorus, which often has mass effect on antrum and duodenum.
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