Cystine calculi--rough and smooth: a new clinical distinction.

Four stones each from 2 populations of cystine calculi, 1 with a rough external surface (cystine-R) and the other smooth (cystine-S), were studied for their crystal structure with stereoscopic and scanning electron microscopy. Two stones each of cystine-R and cystine-S, calcium oxalate monohydrate, calcium oxalate dihydrate, struvite plus apatite and brushite were fragmented with extracorporeal shock wave lithotripsy and the fragmentability was compared. Fragments resulting from cystine-R and cystine-S extracorporeal shock wave lithotripsy were examined under the stereoscope to assess the plane of cleavage or fracture. Results show that cystine-R stones are comprised of well formed blocks of hexagonal crystals, whereas cystine-S calculi have small, irregular and poorly formed interlacing crystals. The center of cystine-R stones was similar to that of the periphery but the center of cystine-S stones was formed of blocks of hexagons similar to but smaller than the cystine-R calculi. Fragmentation with extracorporeal shock wave lithotripsy revealed that cystine-S stones are the least fragile, calcium oxalate dihydrate and struvite plus apatite were the most fragile, and cystine-R, brushite and calcium oxalate monohydrate calculi were in the intermediate fragility range. The possibility of the patient having a cystine-R calculus should be considered during therapeutic procedures.