Sugino Y et al., 2019: The usefulness of the maximum Hounsfield units (HU) in predicting the shockwave lithotripsy outcome for ureteral stones and the proposal of novel indicators using the maximum HU
Sugino Y, Kato T, Furuya S, Sasaki T, Arima K, Sugimura Y.
Department of Nephro-Urologic Surgery and Andrology, Mie University Graduate School of Medicine, Mie, Japan. yusuke.
Department of Urology, Department of Radiology, Yokkaichi Hazu Medical Hospital, Mie, Japan.
Department of Nephro-Urologic Surgery and Andrology, Mie University Graduate School of Medicine, Mie, Japan.
Computed tomography (CT) attenuation value of ureteral stones is one of the predictors of shockwave lithotripsy (SWL) outcome. It is common to use the mean Hounsfield units (HU) to describe the CT attenuation value. However, an observer bias can occur when measuring the mean HU in the conventional method. On the other hand, our way to obtain only the maximum HU is simpler and less biased. We retrospectively evaluated 464 patients with ureteral stones who underwent SWL and compared predictive accuracy of various factors including maximum and mean HU. Results were determined after a single SWL. Predictors of SWL success were examined by the statistical analysis of successful and failed groups. 324 of the 464 patients who underwent SWL were stone-free after a single SWL. Significant differences were found in factors related to CT attenuation value and stone size. As a result of receiver operating characteristic analysis, it was found that maximum HU and mean HU, major diameter and volume have equivalent prediction accuracy, respectively. Multivariate analysis revealed that maximum HU and major diameter were included in independent predictors. We also examined the new original indicators using maximum HU and major diameter. Stone-resistant probability obtained from the logistic model and Maximum HU and Major diameter Index obtained by multiplying maximum HU by major diameter were useful for predicting SWL success, respectively. In conclusion, maximum HU and mean HU have equivalent predictive accuracy, and maximum HU is easier to measure and less biased than mean HU.
Urolithiasis. 2019 Mar 11. doi: 10.1007/s00240-019-01123-3. [Epub ahead of print]
It is well recognized and described in numerous reports that stone hardness as well as stone size are important variables for predicting the outcome of SWL. The hardness is directly determined by the chemical composition and can clinically be estimated by the stone density expressed in Hounsfield units (HU).
It is obvious from this report that HU can be and obviously is measured in two essentially different ways: mean HU and maximum HU. The basic conclusion from the measurements carried out by the authors was that the maximum HU was a better predictor than mean HU for the outcome of SWL of ureteral stones. Personally, I have not used any predictive tools for treating patients with SWL, but when HU levels have been considered, it has always been in terms of the maximum level for the stone.
The other important variable emphasized by the authors was an estimate of the stone size. The conclusion was that the best measurement in this regard was the largest diameter in the axial plane and that this measure had the same accuracy as the stone volume (calculated as the product of long axial diameter x short axial diameter x long coronal diameter!). A clinically useful formula was derived: MMI; major diameter index = maximum HU x largest (major) axial diameter.
The authors also presented some more complicated formulas SRP: stone resistance probabilities, but these expressions most seem to be of theoretical rather than practical value.
There are other interesting notations in this article. The authors treated their patients in a Modulith SLX lithotripter with patients in prone position for both proximal and mid ureteral stones and in supine position for distal ureteral stones. Although several stones certainly are best treated in the prone position the presence of intestinal gas might be a problem. Similarly, it often is necessary to modify the position of the patients when treating stones in the distal ureter, depending on the location of the stone relative to the skeletal structures. Nevertheless, the stone-free rate after one session was approximately 70% which is a good result.