Cystine: helical computerized tomography characterization of rough and smooth calculi in vitro

The classification of cystine stones into rough and smooth varieties has been suggested as an aid to choosing treatment for these difficult stones. Since the surface of stones is difficult to visualize preoperatively, we tested the hypothesis that the surface morphology of cystine stones correlates with their internal structure, as viewed by helical computerized tomography (CT).

Cystine stones were examined visually and categorized into rough (15 stones) and smooth (16 stones) subpopulations of similar size. Each stone was scanned in a helical CT scanner (GE Quad Scanner) to assess radiological characteristics and to measure attenuation values. Scans were also performed using a microCT 20 high resolution laboratory scanner (Scanco Medical AG, Bassersdorf, Switzerland) at 34 microm voxel size and the percent of internal voids was determined.

Mean helical CT attenuation values +/- SD for rough stones were lower than for smooth stones (702 +/- 206 vs 921 +/- 51 HU, p <0.002) and the radiological appearance of rough stones suggested radiolucent voids. Internal voids in rough stones were confirmed using micro CT. Rough cystine stones contained a higher percent of internal voids (0.30% vs 0.06%, p <0.0001).

Rough cystine stones can be distinguished from smooth stones using helical CT in vitro, suggesting that it may be possible to distinguish these stones preoperatively. Since rough cystine stones have been reported to be susceptible to shock wave lithotripsy, the identification of this morphology of cystine stones in the patient using attenuation values and appearance on helical CT could be valuable for planning treatment.