Efficacy of extracorporeal shock wave lithotripsy for solitary lower calyceal stone: a statistical model

To evaluate the effect of inferior calyceal radiographic anatomy, number of extracorporeal shock wave lithotripsy (ESWL) sessions and stone size on the successful clearance of solitary inferior calyceal calculi after ESWL.

In a prospective study between January 2001 and November 2002, 66 renal units with a solitary inferior calyceal calculus of < or = 2 cm were treated with electrohydraulic ESWL. The infundibulopelvic angle (two definitions), infundibulovertebral angle, inferior calyceal infundibular diameter, infundibular length, cortical thickness over the lower pole, number of minor calyces and stone size were determined from intravenous urography before treatment. The number of ESWL sessions was also included in the analysis. Treatments which produced residual fragments not clearing within 3 months of satisfactory fragmentation were considered as failures. All patients in whom the treatment failed were treated successfully by percutaneous nephrolithotomy. The data were then analysed using two different statistical methods; first by intravariable differences using the test of proportion (Fisher's test) and then all the variables together using logistic regression.

At 3 months 78.8% of the renal units were clear of stone. All intravariable differences were statistically significant except stone size (<1 cm, 1-2 cm). In a multivariate analysis of all variables, only stone size was the most important predictor for successful stone clearance (P = 0.03).

ESWL is the initial treatment of choice in selected patients with inferior calyceal stones. The stone size appears to be the most important predictor for stone clearance.