Discrimination between ureteral stent and stone by non-contrast helical computed tomography in the clinical setting

In urolithiasis with indwelling ureteral stent, an adequate visualization of retained stone is often obscured by the stent. In functional solitary kidney, it is essential to detect retained fragments before stent removal. We examined the capability of non-contrast helical computed tomography (NCHCT) in discriminating stone from stent.

We assessed the CT of 21 radiopaque stones of 3-5 mm and four stents, and compared their attenuation values. In addition, two other cases with stent, in which only NCHCT by manipulating the setting could detect retained fragments.

No overlaps of attenuation value were found between the stones and stents. Although they had the same appearance in NCHCT with abdominal-window setting, in bone-window setting the contrasts of stones were reduced, while stents were still bright white.

We would discriminate the residual stone from the stent by manipulating window and level setting, and bone-window setting is easy to use.