Which type of urinary stone is typically lucent and does not appear on a radiograph?

Urate stones are primarily composed of uric acid and are typically radiolucent, meaning they do not show up on standard X-rays. This characteristic is due to the chemical composition of uric acid, which does not have enough mineral content to be detected radiographically. As a result, they can often be overlooked in imaging studies unless other imaging modalities, such as ultrasound or CT scans, are utilized.

Calcium oxalate stones, in contrast, are usually radiopaque and commonly visible on X-rays. Struvite stones and magnesium ammonium phosphate stones are also generally radiopaque due to their mineral composition, making them visible on radiographs as well. Therefore, urate stones stand out because they require different imaging techniques for detection, highlighting the importance of understanding the characteristics of different types of urinary stones in diagnostic practice.