Case
A worried mother brings her 7-week-old infant to your office. She states that the infant is not gaining weight, that he seems to “spit up” everything given to him, and that he still seems hungry after vomiting. On physical examination, he appears thin but not jaundiced. There is a firm, mobile mass in the right upper quadrant (RUQ) of the abdomen. His mucous membranes appear dry. An upper GI series and ultrasonography (US) of the abdomen are performed (see the Figures).What do these images show?
The upper GI series demonstrates elongation and narrowing of the pyloric canal, the so-called “string” sign, along with gastric distention. Notice the wavy appearance of the stomach at its superior aspect. These are peristaltic waves and give the stomach a “caterpillar” appearance. The bulge at the base of the duodenal bulb is compatible with extrinsic compression by the pyloric
muscle. The sonograms demonstrate a thickened pyloric muscle in its transverse axis and elongation of the pyloric canal in its longitudinal axis. The findings of both studies plus the clinical presentation confirm a diagnosis of pyloric stenosis.
Discussion
In pyloric stenosis, the circular muscle of the pylorus of the stomach hypertrophies, which can narrow the pyloric canal and cause symptoms of gastric outlet obstruction. The etiology is unknown. Pyloric stenosis occurs in approximately 1 in 1,000 births and is seen more frequently in males than in females. The symptoms usually manifest at 2 to 8 weeks of age, with most cases diagnosed before the infant is 12 weeks old. Symptoms may include projectile vomiting or spitting up, dehydration, failure to gain weight, persistent hunger, and decreased bowel movements. Jaundice may also develop. The physical examination may reveal a small, firm, movable, palpable mass in the RUQ of the abdomen—sometimes referred to as a palpable olive—which represents the enlarged pylorus muscle of the stomach. The infant may also appear underweight. Peristaltic waves of the stomach may be noticeable. Laboratory studies may demon-strate hypochloremic, hypokalemic metabolic alkalosis. Unconjugated bilirubin levels may be increased.
The differential diagnosis for pyloric stenosis should include gastroesophageal reflux, pyloric atresia, hiatal hernia, and malrotation of bowel. An upper GI series and US are the imaging studies used to evaluate for potential pyloric stenosis.
In the upper GI series, the infant is given barium through a bottle. As the infant consumes the barium, fluoroscopy is used to observe the liquid passing through the esophagus and into the stomach. Swallowing and peristaltic activity as well as anatomy can be assessed. With pyloric stenosis, the stomach may appear distended and may contain retained fluid and air. The caterpillar sign may be present. Gastric emptying may be delayed. The pyloric canal is generally narrowed and elongated (string sign). The enlarged circular muscle of the pylorus can cause a bulging appearance onto the antrum of the stomach (“shoulder sign”) and may bulge into the base of the duodenal bulb.
US is used to measure the thickness of the circular muscle of the pylorus and to measure the length of the pyloric canal. The normal circular muscle thickness should not exceed 4 mm. The length of the pyloric canal may range from 14 to 18 mm.
Treatment of pyloric stenosis includes 
correction of electrolyte imbalances and dehydration as well as an immediate referral for pyloromyotomy, which may be done through an abdominal incision or laparoscopically. Some studies have evaluated nonsurgical treatment with atropine sulfate, but surgical correction remains the gold standard. It is most important to correct the infant's malnourished state and to promote weight gain. JAAPA
The author practices in a radiology group at North Oaks Health System, Hammond, La. She has indicated no relationships to disclose relating to the content of this article.