Combining Mean and Standard Deviation of Hounsfield Unit Measurements from Preoperative CT Allows More Accurate Prediction of Urinary Stone Composition Than Mean Hounsfield Units Alone
INTRODUCTION AND OBJECTIVES: The mineral composition of a urinary stone may influence its surgical and medical treatment. Previous attempts at identifying stone composition based on mean Hounsfield Units (HUm) have had varied success. We aimed to evaluate the additional use of standard deviation of HU (HUsd) to more accurately predict stone composition. METHODS: We identified patients from two centers that had undergone urinary stone treatment between 2006 and 2013 and had mineral stone analysis and a CT available. HUm and HUsd of the stones were compared with ANOVA. ROC analysis with Area Under the Curve (AUC), Youden Index and likelihood ratio calculations were performed. RESULTS: Data was available for 466 patients. The major component was CalciumOxalate Monohydrate (COM), Uric Acid, HydroxyApatite, Struvite, Brushite, Cystine and CO Dihydrate (COD) in 41.4%, 19.3%, 12.4%, 7.5%, 5.8%, 5.4% and 4.7% of the patients respectively. The HUm of UA and Br was respectively significantly lower and higher than the HUm of any other stone type. HUm and HUsd were most accurate in predicting uric acid with an AUC of 0.969 and 0.851 respectively. The combined use of HUm and HUsd resulted in increased positive predictive value and higher likelihood ratios for identifying a stone's mineral composition for all stone types but COM. CONCLUSIONS: To the best of our knowledge this is the first report of CT data aiding in the prediction of brushite stone composition. Both HUm and HUsd can help predict stone composition and their combined use results in higher likelihood ratios influencing probability.