Simple trigonometry on computed tomography helps in planning renal access

To retrospectively assess the usefulness of the measurements on preoperative computed tomography (CT) of patients with urinary stone disease for planning the access site using vertical angulation of the C-arm.

Of the patients who underwent percutaneous nephrolithotomy from November 2001 to October 2006, 41 patients with superior calix access had undergone preoperative CT. The depth of the target stone (y) and the vertical distance from that point to the first rib free slice (x) were measured on CT. The limit of the ratio of x over y was accepted as 0.58, with ratios below that indicating that infracostal access could be achieved by vertical angulation of the C-arm.

We achieved an approach to the superior calix through an infracostal access in 28 patients. The preoperative trigonometric study on CT predicted 24 of them. The stone-free rate was 92.6%, and no chest-related complications developed.

Simple trigonometry on CT of the patients with complex stones could help endourologists in planning renal access.