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Inhomogeneity of kidney calculi do not predict SWL success
Frederikke Eichner Christiansen, Kim Hovgaard Andreassen, Susanne Sloth Osther, and Palle Jörn Sloth Osther.
Urological Research Center, Dept. of Urology, Lillebaelt Hospital, University of Southern Denmark, Fredericia, Denmark.
The infrastructure of kidney calculi determined by pre‐treatment CT-imaging has been suggested as an expression of stone fragility and thereby a predictor for a successful outcome of shockwave lithotripsy (SWL). Invitro studies on cystine and calcium monooxalate stones has shown that inhomogeneous stones required significant less shockwaves than homogeneous stones.
The objective was to evaluate in outcome of in‐vivo SWL in patients with inhomogeneous kidney calculi versus homogeneous stones.
Material & Methods:
257 patients were included. Data were collected by systematic review of the patient’s medical journals and imaging studies. The kidney calculi were categorized from non-contrast CT scans made before the treatment. We evaluated infrastructure of the stones on bone window of the CT-scan using magnification. Imaging follow-up was performed after three months and the number of retreatments was registered. The criteria of success were if the patient were stone free or had fragments less than 4 mm and no symptoms at the three-month evaluation.
At three months follow-‐up 48 ± 5% of the patients with inhomogeneous stones were stone free and 66 ± 5% of the patients obtained the criteria of success. Patients with homogeneous stones had a significantly higher rate of success. 61 ± 4% were stone free and 81 ± 3% obtained the criteria of success at three months (p<0,05). The patients with inhomogeneous had a higher fraction of residuals larger than 4 mm compared to the patients with homogeneous stones, 35 ± 5% vs. 19 ± 3%, RD= 14 % [95% CI: 3‐25%], p<0,05. Patients with inhomogeneous stones required the same amount of retreatments as patients with homogenous stones.
Inhomogeneity of kidney stones as determined on the CT bone window does not seem to predict SWL success in vivo. On the contrary the homogeneous stones had a higher SWL success rate.