Which study is recommended for identifying the underlying etiology in neonates with moderate to severe hydronephrosis?

• A. Family and obstetrical history
• B. Renal ultrasonography
• C. Voiding cystourethrography
• D. Serum creatinine

Answer: (C)

When trying to determine why a newborn has hydronephrosis, you want to know if the dilation is due to refluxing urine back up from the bladder or to an obstruction somewhere in the urinary tract. Voiding cystourethrography directly assesses the lower urinary tract during filling and urination, allowing visualization of any vesicoureteral reflux and identifying obstructive lesions such as posterior urethral valves. This test provides the functional and anatomic information needed to pinpoint the underlying etiology.

While a detailed history can raise suspicion for certain risks, and ultrasound shows the presence and extent of hydronephrosis, neither alone confirms the cause. Serum creatinine tells you about renal function, not the cause of dilation. Therefore, voiding cystourethrography is the test that best identifies why moderate to severe hydronephrosis is present in a neonate.