EAU 2019: Measuring Hounsfield Units in Cystinuria: Is it Really So Hard?

Barcelona, Spain (UroToday.com) Cystine stones are considered difficult and pose a significant challenge in management. Hounsfield units (HU) are often used in other stone types to judge ‘hardness’ and treatments based on stone density. In vitro helical CT scanning of cystine stones allows rough and smooth stones to be differentiated, with rough stones being shown to have lower mean attenuation values than smooth stones. The authors aimed to assess attenuation values of cystine stones in different gene mutations. 

Hannah Warren and colleagues prospectively analyzed a database of cystinuria patients from a single center over a period of 10 years. The mean, minimum and maximum attenuation values of cystine stones in vivo, prior to treatment were measured in HU by drawing a circular region of interest at the center of the stone at its largest diameter. Mean HU in different cystinuria gene mutations was assessed using an independent t-test and HU across multiple stone episodes in an individual was assessed using the paired t-test. Correlation between mean HU and total laser energy utilized at ureteroscopy was also assessed.

In this study among a cohort of 169 adults, cystinuric patients mean HU was 618. There was no difference in mean HU between SLC3A1 and SLC7A9 or between SLC7A9 homo and heterozygous mutations. There was no difference in HU from one independent stone episode to another. Authors highlighted that there was no association between mean HU and total laser energy required to break up the stone at ureteroscopy.

Based on the results of this large, single-center series of cystinuric patients, Dr. Warren concluded that because of the variability of Hounsfield Units are not useful in the judgment of the relative hardness of cystine stones and should not be used for treatment decisions.

Presented by: Hannah Warren, Guy's and St. Thomas' NHS Foundation Trust, Urology Centre, London, United Kingdom

Written by: Ekaterina Laukhtina, Medical Student, Institute for Urology and Reproductive Health, Sechenov University at the 34th European Association of Urology (EAU 2019) #EAU19 conference in Barcelona, Spain, March 15-19, 2019.