Piezoelectric extracorporeal shockwave lithotripsy of distal ureteric calculi: assessment of shockwave focusing with unenhanced spiral computed tomography

Objective To assess the effects of the interposition of pelvic bones and ab dominal gas in the shockwave pathway during piezoelectric extracorporeal sh ock wave lithotripsy (ESWL) of distal ureteric stones. Patients and methods The study included 35 patients who were evaluated with unenhanced spiral computed tomography (CT), used according to their positi oning during ESWL. The shockwave pathway was simulated on the sagittal and coronal views crossing the ureteric calculi, allowing a theoretical evaluat ion of the effective shockwave focusing (with no bone or gas interference). Vertical and oblique approaches were statistically compared for bone and g as interposition. Results Overall, the effective shockwave focusing during in situ piezoelect ric ESWL of distal ureteric stones was 71% of the theoretical area. The int erposition of bone and gas was significantly lower for an oblique access th an for a vertical approach in the sagittal plane (P<0.001 and 0.03 on the s agittal and coronal views, respectively). Using stepwise logistic regressio n, the difference between vertical and oblique accesses in the sagittal pla ne was mainly affected by the bladder volume (P<0.001). On the coronal view s, the interposition of bone and gas affected 31 patients (89%). Such inter ference was eliminated in 73% of the patients with a contralateral inclinat ion of the shockwave axis in the coronal plane. Conclusion The interposition of pelvic bones and abdominal gas in the shock wave pathway can affect the performance of piezoelectric ESWL of distal ure teric stones. While awaiting clinical confirmation of these theoretical dat a, we recommend that patients are treated with the bladder full and that th e shockwave generator is inclined in both the coronal and sagittal planes.