Struvite and cystine calculi are ______ renal calculi.

• A. Radiopaque
• B. Radiolucent
• C. Mixed
• D. Not detectable

Answer: (B)

A key idea here is how renal stones appear on a plain X-ray. Stones vary in radiodensity depending on their mineral content. Radiolucent stones don’t cast a dense shadow on a standard abdominal radiograph, so they aren’t easily seen on X-ray and require other imaging, like noncontrast CT or ultrasound, to be detected.

Struvite and cystine stones are typically not highly radiodense on plain films, so they are considered radiolucent. This is why these stones may be missed on a simple X-ray and why clinicians often rely on CT or ultrasound for imaging when infection-related stones (struvite) or metabolic stones (cystine) are suspected. In contrast, calcium-containing stones are usually radiopaque and readily visible on X-ray.