Renal Location Within the Retroperitoneum in Various Body Positions Using Magnetic Resonance Imaging: Implications for Percutaneous Nephrostolithotomy

Abstract

Objectives: To assess the difference in cranio-caudal renal position in both the supine and prone position, as well as the effect of arm position on renal location, using magnetic resonance imaging in subjects with BMI <30.

Methods: In a prospective IRB approved trial, healthy subjects underwent magnetic resonance imaging in the supine, prone position with arms at the side, and prone position with arms up using vertically placed towel bolsters. Images were obtained with end expiration breath holds. Distances between the kidney and other anatomical landmarks, including the diaphragm (KDD), top of the L1 vertebra (KVD) and lower edge of the 12th rib (KRD), were recorded. Nephrostomy tract length (NTL) and other measures for visceral injury were also assessed. Wilcoxon signed rank test was used for analysis (P < .05).

Results: Ten subjects (5 male, 5 female) with median age of 29 years and BMI of 24 kg/m² were imaged. Right KDD was not significantly different between positions, but KRD and KVD noted significant cephalad movement when prone, as compared to supine. Left KDD noted caudal movement with prone positioning with no difference in KRD or KVD. Arm position did not affect any measurements. Right lower NTL was shorter when prone.

Conclusions: In subjects with BMI < 30, prone positioning led to significant cephalad right renal movement, but not left renal movement. Arm position had no effect on anticipated renal position. Preoperative end expiration supine CT may reliably predict left kidney location and be used to improve preoperative counseling and/or surgical planning.