ABSTRACT
Objective: To assess the pretreatment non contrast helical computed tomography [NCCT] measurements, in the form of, stones Hounsfield unite [HU] and skin to stone distance [SSD] to define the effect of each on extracorporeal shock wave lithotripsy [ESWL] results
Patients and Methods: Twenty eight patients with single renal pelvic [10-20mm] or proximal ureteric stone [5-10mm] had pre-extracorporeal shock wave lithotripsy [ESWL] evaluation by non-contrast computed tomography [NCCT]. Stone attenuation value measured in Hounsfield Unit [HU] as well as skin to stone distance[SSD] was measured on selected NCCT image of interest for each patient, these measures were evaluated as predictors of ESWL outcome. Patients with renal pelvic stones received 3000 shocks per ESWL session while those with proximal ureteric stones received 4000 shocks per session, the maximum ESWL session number allowed were 3 .Patients were evaluated by plain X- ray of the kidney, ureter and bladder [KUB] after each ESWL session. Six weeks after ESWL treatment patients with stones greater than 3mm considered residual stone patients [10 out of 28 patients], while those with complete stone clearance or fragment 3mm or less considered stone- free patients [18 out of 28 patients].The stone attenuation value [HU] and skin to stone distance [SSD] in the stone-free and residual- stone patients group were compared
Results: The overall mean HU value for stone-free and residual-stone patients was significantly different 669 +/- 14.9 HU versus 962 +/- 11.5 HU respectively. The body mass index [BMI] as indicator of overweight or obesity status, go hand in hand with SSD and correlated well with each other, the mean SSD for stone free and residual stone patients were 9.3 +/- 2.7 and 11.4 +/- 3.01 cm respectively, which were statistically significantly different. Analysis of the data revealed that stones of greater than 900 HU were less likely to fragment and ESWL failure is probable[5 patients out of 8, 62.5%]. Furthermore, patients with SSD 10 cm or less had 91.6% stone free rate [11 out of 12 patients], while those with SSD greater than 10 cm had only 43.7% stone free rate [7 patients out of 16]
Conclusion: We concluded that, stone HU and the patients obesity status as expressed by the SSD are powerful predictors of NCCT for ESWL results, so we can save; unnecessary exposure to shock waves, time, effort and costs