Role of Hounsfield Unit in Detecting Stone-Free Rate for Extracorporeal Shock Wave Lithotripsy

Abstract

Background: Urinary stone disease is a common urological condition with a rising global prevalence and significant implications for renal health and healthcare costs. Despite the widespread use of Extracorporeal Shock Wave Lithotripsy (ESWL) as a non-invasive treatment, its success is variable and influenced by several factors, particularly stone density measured in Hounsfield Units (HU). However, inconsistency in HU thresholds and methodological heterogeneity across studies has limited the precision of ESWL outcome prediction. Objective: To evaluate the predictive value of stone density, specifically using a 900 HU threshold, in determining stone-free rates (SFR) following ESWL for renal stones up to 2 cm in the upper and mid-pole of the kidney. Methods: This was a prospective observational study involving 360 patients aged 18–60 years with renal stones ≤20 mm and HU <1500. Patients with lower pole stones, active infections, or contraindications to ESWL were excluded. All CT scans and ESWL procedures were performed using the same equipment and personnel to minimize variability. The primary outcome was stone clearance (≤3 mm on post-treatment CT). Ethical approval was obtained from the institutional board, and all participants provided informed consent in accordance with the Declaration of Helsinki. Data were analyzed using SPSS v27 with descriptive and inferential statistics applied. Results: Of 360 patients, those with HU <900 (n = 187) achieved an 87.71% SFR, while those with HU ≥900 (n = 173) had a significantly lower SFR of 13.29%, indicating a strong inverse correlation between HU and ESWL success. Clinically, stones ≥900 HU showed marked resistance to fragmentation. Conclusion: Stone density significantly predicts ESWL outcomes, with HU ≥900 associated with substantially reduced SFR. Incorporating HU thresholds into treatment planning can optimize patient selection and improve clinical outcomes, reinforcing its utility in personalized management of renal stones.