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Abstract
Purpose
The aim of this study was to determine whether the stone mineral content (SMC) and stone mineral density (SMD), as measured by dual energy X-ray absorptiometry, can predict the stone fragility in extracorporeal shock wave lithotripsy (ESWL).
Materials and Methods
In the experimental study, the stone size, weight, SMC and SMD of 111 urinary calculi, obtained by open surgery, were measured. The SMC and SMD were measured using dual energy X-ray absorptiometry, which is the gold standard for measuring the bone mineral content and density. The number of shock waves necessary for full fragmentation was accepted as a measure of the stone fragility in ESWL (EDAP-sonolith Praktis). In the clinical study, the stone size, SMC and SMD were measured in a total of 48 patients with a solitary renal stone of less than 3cm. Prior to ESWL all patients underwent dual energy X-ray absorptiometry to calculate the SMC and SMD. The correlations between the number of total shock waves and the stone size, SMC and SMD were analyzed.
Results
In the experimental study, the stone size, stone weight, SMC and SMD values correlated with total shock waves, with a correlation coefficients (R) of 0.79, 0.95, 0.99 and 0.86, respectively (n=111). In the clinical study, the mean stone size, mean MC and MD values differed significantly between the clinically successful and failed ESWL (n=36 and n=12), respectively (p=0.0002, p=0.004, p=0.004). On a simple regression analysis, the SMC (R2=0.74), SMD (R2=0.56) and stone size (R2=0.51) were significant factors in predicting the number of shock waves. Using the receiver operating characteristic curves for comparing the stone size, SMC and SMD in relation to the number of shock waves, the areas under the respective curves were 0.79, 0.84 and 0.81 with cut-off values of 1.8, 1.4 and 1.8.
Conclusions
The stone size, SMC and SMD measured by dual energy x-ray absorptiometry may provide a prediction of the outcome of patients prior to ESWL treatment. Patients with high SMC (greater than 1.4gm) could be recommended for percutaneous nephrolithotripsy or another treatment modality, thus, avoiding the unnecessary cost of prior ESWL.
Figures and Tables
Fig. 1
In vitro relationship between (A) stone size, as measured using X-ray and the number of shock waves (y=445.4x-224.1; R2=0.62, p<0.001), (B) stone weight, as measured using electron balance and the number of shock waves (y=182.3x+231.9; R2=0.90, p<0.001), (C) stone mineral content (SMC), as measured using dual energy X-ray absorptiometry and the number of shock waves (y=264.2x+287.9; R2=0.99, p<0.001), (D) stone mineral density (SMD), as measured using dual energy X-ray absorptiometry and the number of shock waves (y=284.7x+281.7; R2=0.75, p<0.001), (E) stone mineral content (SMC), as measured using dual energy X-ray absorptiometry and the stone weight (y=1.31x+0.48; R2=0.90, p<0.001).
Fig. 2
Receiver operating characteristic curves comparing the stone size, SMC and SMD with the number of shock waves. SMC: stone mineral content, SMD: stone mineral density.
Fig. 3
In vivo relationship between (A) stone size, as measured using X-ray and the number of shock waves (y=1195.1x+1540.5; R2=0.51, p<0.0005), (B) stone mineral content (SMC), as measured using dual energy X-ray absorptiometry and the number of shock waves (y=2,416.1x+2,033.9; R2=0.74, p<0.0005), (C) stone mineral density (SMD), as measured using dual energy X-ray absorptiometry and the number of shock waves (y=1,461.1x+2,218.6; R2=0.56, p<0.0005).
Table 7
Sensitivity and specificity calculated for the stone size, SMC and SMD values according to number of shock waves
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