Appearance of urinary tract stones on imaging studies

What is the appearance of urinary tract stones on imaging studies?

The terms radiopaque and nonopaque , when used to describe urinary stones, apply only to the ability to visualize stones on radiographs. All stones, regardless of their composition, are dense on CT and echogenic on US.

Approximately 85% of urinary tract stones are composed of calcium oxalate and are radiopaque (and thus visible) on radiographs (see Figure 33-4, ). Ten percent of stones are composed of uric acid and are either nonopaque or very faintly opaque on radiographs, and they are therefore difficult to identify. Nonopaque stones are invisible on radiographs but are seen as filling defects in the contrast-opacified collecting system. Stones associated with chronic or recurrent infection can grow to fill the entire collecting system (known as “staghorn calculi”) ( Figure 33-7 ). Other stone compositions, such as cystine and xanthine, are less common.


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