To present our experience with extracorporeal shock wave lithotripsy (ESWL) in patients with anomalous kidneys and to determine the factors that may influence the stone-free rate in such patients.

From February 1989 to February 2000, 198 patients were treated for urolithiasis in anomalous kidneys using ESWL. The mean patient age (SD) was 40.48 (11.53) years. The kidneys were horseshoe in 49 (24.7%), malrotated in 120 (60.6%), and duplex in 29 (14.7%). All patients were treated on an outpatient basis using two second-generation lithotripters (Dornier MFL 5000 and Toshiba Echolith). Pretreatment auxiliary measures were required in 6 patients (3%). Follow-up data were recorded at 3 months. The statistical analysis was performed using the chi-square and Mann-Whitney U tests, with differences considered statistically significant if P <0.05.

The mean stone length (SD) was 13.54 (5.49) mm. The stones were single in 148 (74.7%), of new onset in 155 (78.3%), and on the right side in 82 (41.4%). All stones, but 5 (2.5%), were radiopaque. The overall stone-free rate was 72.2%. Neither the type of renal anomaly nor the type of lithotripter had any impact on the stone-free rate (P >0.05). Stone burden (length and number) had a significant influence on the stone-free rate (P <0.05). No extraordinary complications were recorded. Steinstrasse developed in 7 patients (3.5%). No deterioration of renal function or configuration was detected.

ESWL is safe and reliable for treatment of urolithiasis in anomalous kidneys. It should be the primary therapy when the stones are less than 20 mm. The ESWL outcome is comparable for normal and anomalous kidneys when the calculus size is considered.