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The abdominal mass in an infant or child is most commonly an incidental finding first observed by a parent or at the time of a pediatric screening examination. Over 50% of abdominal masses detected by physical examination are actually cases of organomegaly.1,2 The remaining 43% of masses require surgical evaluation and comprise neoplasms, developmental anomalies, and inflammatory or infectious disease. Ninety percent of this group are retroperitoneal masses, approximately half of which derive from the urinary tract.2 In neonates, multicystic dysplastic kidney and hydronephrosis occur in equal frequency and comprise 75% of abdominal masses.2 Older children are more likely to have neoplastic processes.2Table 388-1 lists the most likely diagnoses that vary by location of the mass and age group.

Table 388-1. Differential Diagnosis of Pediatric Abdominal Mass by Location and Age Group

Clinical Features

Most masses are asymptomatic, so the history is rarely diagnostic. Signs and symptoms concerning for malignancy include increased abdominal girth, associated abdominal pain, pain with movement or palpation, constipation, or change in pattern of urination.1 Other helpful elements in the history include signs or symptoms of intestinal obstruction, jaundice, fever, and weight loss. The approximate location of the mass; its mobility, size, and consistency; and any associated developmental anomalies should be noted on physical examination and may be helpful when discussing initial imaging modalities with the radiologist. Ultimately, the age of the patient and physical examination findings narrow the differential diagnosis prior to radiologic imaging.

Diagnostic Evaluation

The radiologic evaluation of the neonatal abdominal mass should begin with abdominal plain films to rule out gastrointestinal obstruction. In contemporary practice, an increasing number of neonatal masses ...

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