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

• A. Abdominal X-ray
• B. Renal ultrasound
• C. CT scan without contrast
• D. MRI of the abdomen

Answer: (B)

Evaluating hydronephrosis or structural abnormalities after urinary obstruction is best done with renal ultrasound. This modality uses sound waves to visualize the kidneys and urinary tract without exposing the patient to radiation, making it safe for most people, including pregnant patients. It can clearly show dilation of the renal pelvis and calyces (hydronephrosis), assess renal cortical thickness, and identify signs of obstruction, providing useful information about the location and impact of the blockage. It’s quick, widely available, and highly effective for confirming hydronephrosis, which guides further management.

Other options have limitations for this purpose. An abdominal X-ray may reveal calcifications but does not reliably show hydronephrosis or the full urinary tract anatomy. A CT scan without contrast can identify stones and offer detailed anatomy, but involves radiation and is not the first-line test for evaluating hydronephrosis itself. MRI gives excellent soft-tissue detail but is more costly, less accessible in acute settings, and not typically needed as the initial test for suspected obstruction.