Correlation of Stone Attenuation Measurement on Non- Contrast Enhanced Computed Tomography with Stone Fragmentation Using Extracorporeal Shock Wave Lithotripsy in Upper Urinary Calculi

Abstract

Extracorporeal shock wave lithotripsy (ESWL) has been extensively used in management of urinary calculi, however its success rate is variable depending upon the size and attenuation value of stones. Non-contrast computed tomography (NCCT) can accurately measure these parameters. The purpose of present study was to assess role of NCCT Hounsfield unit (HU) measurement in upper urinary calculi for predicting success rate of ESWL. Material and methods: The present prospective study was conducted in 30 subjects with symptomatic radio-opaque solitary renal or upper ureter calculus measuring 5-20mm. Patients were divided into two groups (A and B), depending on the CT attenuation values of less or more than 750 HUs respectively. All treatment was done by an electromagnetic lithotripter (Dornier Compact Delta, Singapore) under fluoroscopic guidance. Cases of residual fragments larger than 5 mm or of a stone that did not fragment satisfactorily were considered failures. Mean HU per stone was compared in the stone free and residual stone groups. Results: Out of 30 subjects, 17 belonged to group A (stone HU value <750HU) and 13 belonged to group B (stone attenuation value ≥750HU). The mean number of shock waves delivered in two groups A and B were 4411.76 and 7615.38 respectively (p<0.0001). Mean stone size in group A was 1.51cm and that in group B was 1.59 (p value-0.5346). The stone clearance rate in Group A was 100% versus Group B where it was only 15.4% (p <0.001). Overall, mean attenuation values for the stonefree and residual stone groups were significantly different (514.10 versus 970.36 HU, respectively, p <0.0001). Conclusion: NCCT attenuation value has inverse relationship with ESWL outcome with poor response at HU value ≥750HU.