Objectives
To determine whether stone attenuation and the skin-to-stone distance (SSD) can predict
for stone fragmentation by SWL independently. Identifying the factors predictive of
shock wave lithotripsy (SWL) outcome would help streamline the care of patients with
stones.
Methods
A retrospective review was performed of 111 patients undergoing initial SWL for a
solitary, 5-20 mm, renal calculus. Stone size, location, attenuation value, and SSD
were determined on pretreatment noncontrast computed tomography. The outcome was categorized
as stone free, complete fragmentation <5 mm, and incomplete fragmentation ≥5 mm or
unchanged at 2 weeks on kidney/ureter/bladder radiography.
Results
After SWL, 44 (40%) were stone free, 27 (24%) had complete fragmentation, and 40 (36%)
of 111 patients had incomplete fragmentation. The stone attenuation of the successfully
treated patients (stone free and complete fragmentation groups) was 837 ± 277 Hounsfield
units (HU) vs 1092 ± 254 HU for those with treatment failure (incomplete fragmentation;
P < .01). The mean SSD also differed: 9.6 cm ± 2.0 vs 11.1 cm ± 2.5 for the successful
treatment group vs the treatment failure group, respectively (P = .01). On multivariate analysis, the factors that independently predicted the outcome
were stone attenuation, SSD, and stone composition. When patients were stratified
into 4 risk groups (stone <900 HU and SSD <9.0 cm, stone <900 HU and SSD ≥9.0 cm,
stone ≥900 HU and SSD <9.0 cm, and stone ≥900 HU and SSD ≥9.0 cm), the SWL success
rate was 91%, 79%, 58%, and 41%, respectively (odds ratio 7.1, 95% confidence interval
1.6-32 for <900 HU and SSD <9.0 cm group vs other 3 risk groups; P = .01).
Conclusions
The results of our study have shown that a stone attenuation of <900 HU, SSD of <9
cm, and stone composition predict for SWL success, independent of stone size, location,
and body mass index. These factors will be considered important in the prospective
design of a SWL treatment nomogram at our center.
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Article info
Publication history
Published online: July 31, 2008
Accepted:
May 13,
2008
Received:
June 19,
2007
Identification
Copyright
© 2008 Elsevier Inc. Published by Elsevier Inc. All rights reserved.
