FMGE 2017 — Radiology

Question 1: Which of the following is a gold standard investigation for diagnosis of renal stone?

• A. Helical CT with Non-contrast (Correct Answer)
• B. USG
• C. Helical CT with contrast
• D. MRI

Explanation: ***Helical CT with Non-contrast*** - **Non-contrast helical CT** (also known as CT KUB) is considered the **gold standard** due to its high sensitivity and specificity for detecting all types of urinary tract calculi, regardless of their composition. - It rapidly identifies stones, their location, size, and associated complications like **hydronephrosis**, without the need for IV contrast. *USG* - **Ultrasound** is a good initial screening tool and can detect larger stones and hydronephrosis, but its sensitivity is lower than CT, especially for smaller stones or those in the ureters. - Its diagnostic accuracy is highly **operator-dependent**, and it may miss stones obscured by bowel gas or bone. *Helical CT with contrast* - While helical CT is excellent, the use of **IV contrast** is generally avoided for routine stone detection as it can obscure the highly dense stones from the contrast-enhanced renal collecting system. - Contrast is primarily useful for evaluating **renal masses**, infection, or vascular abnormalities, not for primary stone diagnosis. *MRI* - **MRI** has limited utility in detecting typical renal stones because most calculi are not well-visualized on standard MRI sequences due to their lack of free water and low signal intensity. - It may be considered in specific populations, such as **pregnant women** or children, to avoid radiation exposure, but it is not the gold standard for stone detection.