Korean J Urol.  2012 Jan;53(1):40-43. 10.4111/kju.2012.53.1.40.

Analyzing the Effect of Distance from Skin to Stone by Computed Tomography Scan on the Extracorporeal Shock Wave Lithotripsy Stone-Free Rate of Renal Stones

• Park BH
• Choi H
• Kim JB
• Chang YS

• KMID: 1988822
• DOI: http://doi.org/10.4111/kju.2012.53.1.40

Abstract

PURPOSE
To determine whether the distance from skin to stone, as measured by computed tomography (CT) scans, could affect the stone-free rate achieved via extracorporeal shock wave lithotripsy (ESWL) in renal stone patients.
MATERIALS AND METHODS
We retrospectively reviewed the records 573 patients who had undergone ESWL at our institution between January 2006 and January 2010 for urinary stones sized from about 5 mm to 20 mm and who had no evidence of stone movement. We excluded patients with ureteral catheters and percutaneous nephrostomy patients; ultimately, only 43 patients fulfilled our inclusion criteria. We classified the success group as those patients whose stones had disappeared on a CT scan or simple X-ray within 6 weeks after ESWL and the failure group as those patients in whom residual stone fragments remained on a CT scan or simple X-ray after 6 weeks. We analyzed the differences between the two groups in age, sex, size of stone, skin-to-stone distance (SSD), stone location, density (Hounsfield unit: HU), voltage (kV), and the number of shocks delivered.
RESULTS
The success group included 33 patients and the failure group included 10. In the univariate and multivariate analysis, age, sex, size of stone, stone location, HU, kV and the number of shocks delivered did not differ significantly between the two groups. Only SSD was a factor influencing success: the success group clearly had a shorter SSD (78.25+/-12.15 mm) than did the failure group (92.03+/-14.51 mm). The results of the multivariate logistic regression analysis showed SSD to be the only significant independent predictor of the ESWL stone-free rate.
CONCLUSIONS
SSD can be readily measured by CT scan; the ESWL stone-free rate was inversely proportional to SSD in renal stone patients. SSD may therefore be a useful clinical predictive factor of the success of ESWL on renal stones.

Keyword

ESWL; Lithotripsy; Tomography; spiral computed

MeSH Terms

Humans
Lithotripsy
Logistic Models
Multivariate Analysis
Nephrostomy, Percutaneous
Retrospective Studies
Shock
Silver Sulfadiazine
Skin
Urinary Calculi
Urinary Catheters
Silver Sulfadiazine

Figure

• 

  FIG. 1 The measurement of skin-to-stone distance at 45° on an axial scan of non-contrast computed tomography. SSD: skin to stone distance.

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