Which imaging modality is listed for hydronephrosis evaluation?

• A. Ultrasound
• B. MRI with contrast
• C. CT scan without contrast
• D. PET-CT

Answer: (C)

Hydronephrosis is usually evaluated to find an obstruction in the urinary tract, most often a stone blocking flow. A non-contrast CT scan is ideal here because it is very sensitive for detecting renal calculi and can also show dilation of the kidney’s collecting system. This combination helps identify or rule out stones as the cause of the obstruction quickly and definitively, without the potential masking effects of contrast.

Ultrasound can reveal hydronephrosis and is safe and useful as an initial, radiation-free screen, but it is less reliable for identifying stones. MRI with contrast is not typically needed for stone-related obstruction and carries more cost and risks; PET-CT is not used for hydronephrosis evaluation.