Nakasato T et al, 2014: Evaluation of Hounsfield Units as a predictive factor for the outcome of extracorporeal shock wave lithotripsy and stone composition.
Nakasato T, Morita J, Ogawa Y
Department of Urology School of Medicine, Showa University, 1-5-8, Hatanodai, Shinagawa-ku, Tokyo, 142-8666, Japan.
The objective of this study was to evaluate the utility of the Hounsfield Unit (HU) values as a predictive factor of extracorporeal shock wave lithotripsy outcome for ureteral and renal stones. We also assessed the possibility that HU values could be used to predict stone composition. A retrospective study was performed to measure stone HU values in 260 patients who underwent extracorporeal shock
wave lithotripsy (ESWL) for solitary renal and ureteral stones from July 2007 to January 2012. Stone volume, location, skin-to-stone distance, stone HU values, and stone composition were assessed. Success of ESWL was defined as: (1) being stone-free or (2) residual stone fragments <4 mm after 3 months by radiography. Of the 260 assessed patients, 141 (54.2 %) were stone-free, 32 (12.3 %) had residual stone fragments <4 mm (clinically insignificant stone fragments), and 87 (33.5 %) had residual stone fragments ≥4 mm after one round of ESWL. Multivariate analysis revealed that stone location and mean HU were significant predictors of ESWL success. Receiver operating characteristic curves defined cutoff values for predicting treatment outcome. Treatment success rates were significantly higher for stones <815 HU than with stones >815 HU (P < 0.0265). HU of calcium oxalate and calcium phosphate stones were higher than those of uric acid stones, but we could not differentiate between calcium oxalate monohydrate and calcium oxalate dihydrate stones. Evaluation of stone HU values prior to ESWL can predict treatment outcome and aid in the development of treatment strategies.
Urolithiasis. 2014 Aug 20. [Epub ahead of print]
Since a good 30 years many papers on CT based determination of in vivo stone composition have been published. By now the question what to expect by CT techniques should be settled. But there is obviously no consensus about a procedural standard and which machine and what protocol should be used. The authors had the ambitious goal to reliably detect stones with different calcium oxalate monohydrate content and failed. This was to be expected because of two reasons: Stone analysis was obtained by “A portion of the broken stone was sent to an outside institution and infrared absorption spectrophotometry was performed to evaluate its chemical composition.” Stones are composed of different layers which react different on shock waves. A small fragment is barely representative of the whole stone. In addition unfortunately the stone analysis results of commercial labs are not reliable (Krambeck et al. Inaccurate reporting of mineral composition by commercial stone analysis laboratories: implications for infection and metabolic stones. J Urol. 2010 Oct; 184(4):1543-9).