Predicting the Therapeutic Effect of Extracorporeal Shockwave Lithotripsy by Non-enhanced Computed Tomography in Renal Stones

Jung Hoon Kim; Young Tae Moon

doi:10.4111/kju.2008.49.3.252

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Kim and Moon: Predicting the Therapeutic Effect of Extracorporeal Shockwave Lithotripsy by Non-enhanced Computed Tomography in Renal Stones

Original Article

Korean J Urol 2008;49(3):252-256.

Published online: 17 January 2008

DOI: https://doi.org/10.4111/kju.2008.49.3.252

Predicting the Therapeutic Effect of Extracorporeal Shockwave Lithotripsy by Non-enhanced Computed Tomography in Renal Stones

Jung Hoon Kim, Young Tae Moon

¹Department of Urology, College of Medicine, Chung-Ang University, Seoul, Korea

교신저자: 문영태 중앙대학교병원 비뇨기과 서울특별시 동작구 흑석동 224-1 156-861 TEL: 02-6299-1809, 1788 FAX: 02-6294-1406 E-mail: moon13579@hanafos.com

Revised 7 January 2008 Accepted 4 February 2008

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Purpose

To evaluate the value of non-enhanced computed tomography (NECT) as a predictor of renal stone destruction by the use of extracorporeal shock wave lithotripsy (SWL).

Materials and Methods

The study included 34 patients with a renal stone diagnosed by NECT. The stone location and size, body mass index (BMI), Hounsfield units (HU) density, and skin-to-stone distance (SSD) were assessed. The SSD was calculated by averaging three distances from the skin to the stone (at 0^o, 45^o and 90^o angles) on NECT. The HU density was evaluated by measuring three different areas of the stone on NECT. Failure of disintegration was defined as no fragmentation or expulsion of the stone after three sessions of SWL.

Results

Failure of disintegration was observed in 14 patients (41.2%). The mean SSD was 8.70±0.75cm for patients where SWL failed to disintegrate the stone (failure group) versus 6.90±1.19cm for patients where SWL successfully disintegrated the stone (success group) (p＜0.01). The mean BMI of the failure group (26.37±2.29kg/m²) was significantly higher than that of the success group (23.36±3.48kg/m²) (p＜0.01). Stone laterality, size, and HU density were not related to the stone fragmentation rate (p＞0.05). By multivariate analysis, SSD was found to independently decrease the stone fragmentation rate of a renal stone (p=0.013; odds ratio=6.219).

Conclusions

The SSD on NECT and BMI may predict the success of SWL for a renal stone.

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Keywords: Tomography, Lithotripsy, Urinary calculi

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Fig. 1.

The measurement of skin-to-stone distance at 0^o, 45^o, and 90^o on an axial scan of non-enhanced computed tomography.

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Fig. 2.

A receiver operating characteristic curve demonstrating the area under the curve of 0.911. An SSD of 8cm represented the most sensitive (87%) and specific (79%) point on the curve.

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Table 1.

Comparison of characteristics in the ESWL-success group of patients and ESWL-fail group of patients

	Success mean±SD	Failure mean±SD	p-value^∗
Age (year)	56.95±16.79	62.50±12.46	0.302
BMI (kg/m²)	23.36±3.48	26.37±2.29	0.008
Hounsfield units (HU)	570.15±339.99	783.50±429.79	0.116
Stone size (mm)	9.50±6.04	13.21±7.46	0.109
SSD (cm)	6.90±1.19	8.70±0.75	＜0.001

^∗ : Student's t-test, ESWL: extracorporeal shock wave lithotripsy, BMI: body mass index, SSD: skin-to-stone distance, SD: standard deviation

Table 2.

Univariate analysis for categorical variables predicting failure of disintegration by extracorporeal shock wave lithotripsy

	n	No. of failures (%)	p-value^∗
Gender			0.774
Male	18	7 (38.9)
Female	16	7 (43.8)
Obesity			0.005
Not obese	17	3 (17.6)
Obese	17	11 (64.7)
Laterality			1.000
Right	17	7 (41.2)
Left	17	7 (41.2)
Stone attenuation			0.187
＜1,000 HU	25	9 (36.0)
≥1,000 HU	8	5 (62.5)
Skin-to-stone distance			＜0.001
＜8cm	21	3 (14.3)
≥8cm	13	11 (84.6)

^∗ : chi-square test, HU: hounsfield units

Table 3.

Multivariate analysis of the ESWL success rate according to the parameters by multiple logistic regression analysis

	Odds ratio	95% confidence interval		p-value^∗
	Odds ratio	Lower	Upper	p-value^∗
Age	0.054	0.935	1.089	0.816
BMI	0.066	0.663	1.708	0.797
Hounsfield units	0.053	0.997	1.003	0.818
Stone size	1.669	0.935	1.387	0.196
SSD	6.219	1.046	1.458	0.013

^∗ : logistic regression analysis, ESWL: extracorporeal shock wave lithotripsy, BMI: body mass index, SSD: skin-to-stone distance

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