Can Hounsfield Unit Value Predict Type of Urinary Stones?

Abstract

Aim: Aim of this study is to determine the role of Hounsfield unit (HU) in predicting results of stone analysis. Material and Method: This study included 199 patients to whom percutaneous nephrolithotomy (PNL) procedures were applied between January 2008 and May 2011 in our clinic. Before the procedure HU values of kidney stones were measured using non-contrast computed tomography. After the operation, obtained stone samples were analysed using X-ray diffraction technique. HU values were compared with stone analysis results. Results: Stone analysis revealed eight different stone types. Distribution of stone types and HU value ranges were as follows: 85% calcium oxalate monohydrate, 730-1130 HU; 38% calcium oxalate dihydrate, 510-810 HU; 21% uric acid, 320-550 HU; 23% struvite, 614-870 HU; 7% calcium hydrogene phosphate, 1100-1365 HU; 3% cystine, 630-674 HU; 15% mixed uric acid plus calcium oxalate, 499-840 HU; and 7% mixed cystine plus calcium phosphate, 430-520 HU. HU values of all stone types ranged between 320 and 1365. There was a statistically significant relation between HU values of uric acid and non uric acid stones (p<0,001). There was a statistically significant difference between HU values of pure calcium and non calcium stones (p<0,001). No statistically significant relation was detected between HU values of struvite and non struvite stones (p=0,110). Discussion: Although there were significant differences between stone types in our study, stone types were not be able to differentiated precisely by HU value measurements due to frequent overlapping in HU values of stone types.