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Acute abdominal pain is a common presenting complaint in pediatric emergency departments, accounting for approximately 5% of all visits.1 The pain often stems from relatively benign processes, nonspecific causes, or constipation. A more common although less benign condition is the often predicted appendicitis, a diagnosis toward the top of the differential for many children with abdominal pain. Appendicitis should particularly be suspected when the child has low-grade temperature, pain in the right lower quadrant, or, classically, pain that migrates from the periumbilical area to McBurney’s point, often accompanied by anorexia and vomiting.

The astute clinician, however, must always consider the less common but more insidious etiologies of pediatric abdominal pain that may require surgical intervention. Some “red flags” that indicate a more serious underlying etiology include peritoneal signs, bloody diarrhea, pain that awakens the child from sleep, and bilious vomiting.

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The following case series presents some of the more serious etiologies of acute abdominal pain in the pediatric population seen at an academic pediatric emergency department over a 3-year period. Although not very common, these etiologies should be considered while building a comprehensive differential diagnosis.

Case #1: Pyloric stenosis

A 22-day-old, full-term, first-born male who had been healthy previously was brought to the emergency department with persistent vomiting after meals. Although his parents switched formulas on two occasions, postprandial vomiting continued. Other than the child being slightly underweight for his age, the physical examination was unremarkable. Plain films were obtained and showed a dilated, air-filled stomach; routine labs revealed mild hypokalemia with a hypochloremic metabolic alkalosis, and were otherwise normal. An abdominal ultrasound (US) confirmed the diagnosis by revealing the presence of a thickened and elongated pylorus. The child was admitted to correct the electrolyte abnormalities and to receive a surgical pyloromyotomy; he was discharged home without complication.

Pyloric stenosis can occur in both male and female infants, but the condition is almost 4 times more likely in males, especially when they are the firstborn.2,3 Most infants present between age 2 weeks and age 5 weeks. The patient in this case exhibited the typical presentation of pyloric stenosis: projectile, nonbilious vomiting that occurs shortly after feedings. A key feature in the diagnosis is the infant’s desire to feed again soon after vomiting. At presentation, infants are often dehydrated and may have a hypokalemic, hypochloremic metabolic alkalosis. The finding of an olive-shaped mass in the right upper quadrant, best felt immediately following emesis, is pathognomonic of the disorder; however, this is only palpated in 60% to 80% of infants.

When a child presents with severe abdominal symptoms, what is usually your first move:

In this patient, the radiographic findings were suggestive of pyloric stenosis: gastric distention with air and a gastric diameter greater than 6 cm with the presence of bowel gas in the lower quadrants (Figure 1). Increased length and thickness of the pyloric muscle as seen on US (Figure 2) were diagnostic: greater than 15 mm and 4 mm, respectively.4

Figure 1. Abdominal x-ray of pyloric stenosis shows the large, dilated, air-filled stomach with air in the small intestine.

Figure 2. Ultrasound reveals elongated and thickened pylorus muscle wall in pyloric stenosis.

In such cases, after treating the dehydration and correcting any metabolic disturbances, a surgical pyloromyotomy is performed, consisting of dividing the muscles of the pylorus, and the child is usually discharged a few days later.5