Which imaging modality is used to evaluate hydronephrosis after urinary obstruction?

• A. Mammography
• B. Renal ultrasound
• C. Plain X-ray of the abdomen
• D. Echocardiography

Answer: (B)

Hydronephrosis from urinary obstruction is best evaluated with renal ultrasound. Ultrasound directly visualizes dilation of the renal pelvis and calyces, allowing you to see the extent of hydronephrosis and any accompanying hydroureter. It also helps assess kidney size and cortical thickness, which can indicate chronicity, and can evaluate the bladder for post-void residual to gauge obstruction. Importantly, it’s noninvasive, uses no ionizing radiation, and can be repeated easily, which is ideal for monitoring response after relief of obstruction or during follow-up.

Other options don’t fit as well. Mammography has no role in assessing the urinary tract. A plain abdominal X-ray may miss hydronephrosis, as it is not sensitive for collecting-system dilation and prints only limited information about soft tissues. Echocardiography focuses on the heart, not the urinary tract. If more detail about the cause of obstruction is needed, CT urography or MRI can be used, but renal ultrasound is the standard initial imaging to evaluate hydronephrosis.