Background and Purpose: Percutaneous nephrolithotomy (PCNL) in the prone position is associated with a 0.1% risk of colon injury, yet there have not been any reported cases of colon injury with supine PCNL. The aim of the present study was to prospectively compare CT scans of patients performed in both supine and prone positions on bolsters. Patients and Methods: Sixteen consecutive patients (mean age 55, 12 men) with 19 renal units (3 bilateral) who presented for PCNL underwent preoperative supine (without bolsters) and prone (with bolsters) noninfused CT scans. Axial images through lower pole calices containing stones necessitating percutaneous access were then analyzed. Percutaneous access was planned based on both supine and prone CT scans. Skin-to-stone distance (cm), angle of the percutaneous tract to the anterior-posterior axis (degrees), and visceral organ-to-tract distance (cm) were measured. Results: Visceral organ-to-tract distance was significantly shorter in the prone position when compared with the supine position (2.8 cm vs 3.5 cm, P=0.04). In three renal units, visceral organ-to-tract distance in the prone position was less than 0.4 cm. Furthermore, the prone position was associated with significantly shorter skin-to-stone distance (7.6 cm vs 9.0 cm, P=0.0005) and significantly wider angles (40 degrees vs 35 degrees, P=0.02). Small sample size and simulation of the percutaneous access tract are two limitations of the present study. Conclusions: When prone PCNL is contemplated, preoperative planning CT scans that are performed in the prone position with bolsters provide better preoperative assessment of colon-to-percutaneous renal tract distance.
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