[Effects of chemical and radiographic factors on the treatment of renal lithiasis using extracorporeal external shock-wave lithotripsy].

The systematic collection and filtration of urine for three days after extracorporeal shock wave lithotripsy (ECSWL) has enabled the chemical analysis of the stones treated in 90% of cases. We have been able to demonstrate a correlation between the chemical nature and the mode of fragmentation of the stones. Calcium oxalate monohydrate, brushite and cystine stones form fairly large, well separated, angular fragments with sharp edges. Calcium oxalate dihydrate, calcium phosphate and magnesium ammonium-phosphate (struvite) stones are reduced to an amorphous dust. These findings have direct therapeutic implications, as it is absolutely essential to make sure that no large stone fragments are left in the urinary tract after lithotripsy. These elements led us to try to evaluate the chemical nature and the hardness of the stones on the basis of the radiological findings, in order to adopt the best possible therapeutic strategy. Calcium oxalate dihydrate stones have a striated, spiky and non-homogeneous appearance on plain X-rays. They are frequently responsible for filling defects on intravenous pyelography. They are friable stones which are easily fragmented. In contrast, calcium oxalate monohydrate stones present a regular homogeneous opacity on plain X-rays with no filling defect on intravenous pyelography. These stones are hard and are broken up, with difficulty, into large fragments on the initial fluoroscopic images at the start of treatment. Many stones have a mixed composition (calcium oxalate monohydrate, calcium oxalate dihydrate and calcium phosphates): the plain X-ray does not provide sufficient information and the presence of a filling defect on intravenous pyelography may or may not be suggestive of a friable stone.(ABSTRACT TRUNCATED AT 250 WORDS)