Next Step in Diagnostic Workup: Ultrasound
For a 4-year-old child presenting with a right flank mass and normal blood pressure, ultrasound (US) is the next step in diagnostic workup.
Rationale for Ultrasound as First-Line Imaging
Ultrasound is the recommended initial imaging modality for pediatric abdominal masses because it is non-invasive, does not involve ionizing radiation, is readily available, and can effectively characterize most pediatric abdominal masses 1.
In the pediatric population, ultrasound establishes the presence of a mass (as nonneoplastic entities can mimic masses), identifies characteristic imaging features that narrow the differential diagnosis, and helps determine whether the mass is solid or cystic 1.
Renal ultrasound is specifically recommended by the American Academy of Pediatrics for evaluating children with hypertension to assess for kidney size discrepancy, hydronephrosis, cystic disease, or other structural abnormalities 2. While this child has normal BP, the same imaging approach applies to flank masses.
Why Not Other Imaging Modalities First?
Plain radiography (X-ray) has limited utility as the initial study for abdominal masses in children, as it provides minimal soft tissue characterization and cannot adequately differentiate between various mass types 1, 3.
CT and MRI should be reserved for further characterization after ultrasound has established the presence and basic characteristics of the mass, or when ultrasound findings are inconclusive 1, 3.
CT involves significant radiation exposure in a young child, and MRI often requires sedation in this age group, making both less appropriate as initial screening tools 1.
Clinical Context for a 4-Year-Old with Flank Mass
The most common abdominal masses in this age group include Wilms' tumor (nephroblastoma), neuroblastoma, hydronephrosis, and multicystic dysplastic kidney 4, 5.
The normal blood pressure is reassuring but does not exclude serious pathology. Hypertension occurs in only a subset of children with renal masses 2.
A thorough history should focus on: perinatal complications, urinary symptoms, hematuria, fever, weight loss, and family history of renal disease or malignancy 2, 4.
Physical examination should assess: the mass characteristics (size, mobility, consistency), presence of other abdominal masses, hepatosplenomegaly, and signs of systemic illness 2, 4.
Subsequent Workup After Ultrasound
If ultrasound identifies a renal mass suspicious for malignancy (such as Wilms' tumor), CT or MRI will be needed for staging and surgical planning 1, 4.
Basic laboratory studies should include: complete blood count, comprehensive metabolic panel with renal function, urinalysis, and urinary catecholamines if neuroblastoma is suspected 2, 4.
Immediate referral to pediatric oncology or urology is warranted if imaging suggests a malignant process 4.
Answer: B. US (Ultrasound)