Which imaging modality is typically used first to evaluate suspected hydronephrosis in a neonate?

• A. Renal ultrasonography
• B. Voiding cystourethrography
• C. MRI
• D. CT

Answer: (A)

Hydronephrosis in a newborn is typically evaluated first with renal ultrasonography because it is safe, noninvasive, and readily available, with no radiation exposure. Ultrasound can confirm dilation of the renal pelvis and calyces, assess the renal parenchyma, and evaluate the bladder and collecting system to help determine if the dilation suggests obstruction or a reflux-related process. This information guides immediate management and helps decide whether further tests are needed. If obstruction or reflux is suspected after ultrasound, other studies like a voiding cystourethrogram can be used. CT and MRI are not first-line in neonates due to radiation exposure (CT) or higher cost and need for longer, sometimes sedated imaging (MRI).