Preoperative planning with noncontrast computed tomography in the prone and supine position for percutaneous nephrolithotomy: a practical overview.

Objective: To evaluate kidney/adjacent organs positional changes in patients undergoing percutaneous nephrolithotomy (PCNL) using noncontrast computed tomography (NCCT) in prone and supine positions.

Methods: Patients scheduled PCNL were prospectively enrolled in the study and underwent NCCT in supine and in prone position (with boosters). Two imaginary lines for the posterior calyx of upper/mid/lower poles of both kidneys in prone and supine decubitus were considered and compared. Line I (LI): drawn horizontally in the coronal plane in contact with the posterior edge of the kidney. Line II (LII): drawn from the antero-lateral edge of the vertebra through the middle of the posterior calyx (ideal puncture line). Renal depth (d) was measured from LI to the anterior extremity of the vertebra. The maximum access angle (a) considered the window available in the axial plane to perform a secure approach to each calyx.

Results: Thirty-seven patients were analyzed; 56.7% were female; mean BMI was 28.3±4.9 kg/m(2). For the right kidney, prone position was associated with more organs crossed by LI (54.1% vs 18.9%; p<0.01) and LII (56.8% vs 27%; p=0.03) in the upper calyx. For the left kidney, LII crossed more organs in prone in the upper calyx (54.1% vs 29.7%; p=0.03). Both kidneys showed a tendency to be deeper in the supine position, which provided a wider access angle.

Conclusions: Supine NCCT is not accurate to plan PCNL access in prone position. Prone decubitus is associated with more potential organ injuries in the upper pole. In supine, the kidney situates deeper in the abdomen but the access angle is wider than in prone.