Which imaging modality is most commonly used first when nephrolithiasis is suspected?

• A. Ultrasound
• B. Non-contrast CT abdomen/pelvis
• C. IV pyelography
• D. KUB radiographs

Answer: (B)

When nephrolithiasis is suspected, non-contrast CT of the abdomen and pelvis is the first-line imaging because it quickly and reliably detects stones of all compositions and locations, and it can reveal other causes of acute flank or abdominal pain in a single study. It doesn’t require contrast, is widely available, and has high sensitivity and specificity, which helps with accurate diagnosis and prompt management.

Ultrasound is useful in specific situations, such as in pregnant patients, children, or when avoiding radiation is important, and it can show hydronephrosis, but it is less reliable for detecting stones, especially small or tightly located ureteral stones. KUB radiographs can miss many stones (only radiopaque stones are seen well) and often underestimate or miss stones entirely. IV pyelography is largely obsolete due to lower sensitivity, the need for contrast, and availability of CT.