Pyloric Stenosis - Diagnosis

Diagnosis

Diagnosis is via a careful history and physical examination, often supplemented by radiographic studies. There should be suspicion for pyloric stenosis in any young infant with severe vomiting. On exam, palpation of the abdomen may reveal a mass in the epigastrium. This mass, which consists of the enlarged pylorus, is referred to as the 'olive', and is sometimes evident after the infant is given formula to drink. It is an elusive diagnostic skill requiring much patience and experience. There are often palpable (or even visible) peristaltic waves due to the stomach trying to force its contents past the narrowed pyloric outlet.

Most cases of pyloric stenosis are diagnosed/confirmed with ultrasound, if available, showing the thickened pylorus. Although somewhat less useful, an upper GI series (x-rays taken after the baby drinks a special contrast agent) can be diagnostic by showing the narrowed pyloric outlet filled with a thin stream of contrast material; a "string sign" or the "railroad track sign". For either type of study, there are specific measurement criteria used to identify the abnormal results. Plain x-rays of the abdomen are not useful, except when needed to rule out other problems.

Blood tests will reveal hypokalemic, hypochloremic metabolic alkalosis due to loss of gastric acid (which contain hydrochloric acid and potassium) via persistent vomiting; these findings can be seen with severe vomiting from any cause. The potassium is decreased further by the body's release of aldosterone, in an attempt to compensate for the hypovolaemia due to the severe vomiting.