Anatomical variation between the prone, supine, and supine oblique positions on computed tomography: Implications for percutaneous nephrolithotomy access

To determine anatomical variations between the prone, supine, and supine oblique positions that are likely to affect percutaneous renal access. Twenty patients underwent computed tomography urograms in the supine and prone positions. Twenty patients underwent supine oblique and prone scans. Mean nephrostomy tract length, maximum access angle, and anteriorposterior renal position were calculated. Mean nephrostomy tract length was shorter in the prone position (82.6 mm right kidney, 85.4 mm left kidney) compared with the supine position (108.3 mm right kidney, P <.001; 103.7 mm left kidney, P <.001). Prone tract length was also shorter than supine oblique tract length (86.1 mm vs 96.5 mm; P =.048). Mean maximum access angle was significantly greater (P =.018 right kidney; P =.007 left kidney) in the prone position (right kidney 99.7°, left kidney 104.0°) compared with the supine position (right kidney 87.7°, left kidney 89.4°). The same was true for the prone compared with the supine oblique position (75.8° vs 58.7°; P =.004). No difference was noted in anteriorposterior renal position between the supine and prone positions (20.3 mm vs 26.7 mm; P =.094) or supine oblique and prone positions (22.8 mm vs 15.6 mm; P =.45). The prone position is associated with a significantly shorter nephrostomy tract length and more potential access sites, which may improve ease and safety of percutaneous renal access.