Renal Displacement with Supine to Prone Positional Change: Effect of Sex and Body Mass Index.

To determine patterns of kidney and retroperitoneal organ movement during positional change between the supine and prone positions as seen on CT scans. Axial CT scans of 75 subjects who underwent supine and prone positions were retrospectively analyzed. A total of 1650 measurements were taken for anterior/posterior, medial/lateral, cranial/caudal, skin-to-calix distance, kidney-to-liver distance, and kidney-to-colon distance in both positions. Pronation shortens the distance from the skin to renal calix for both the right (99.62 mm 85.14 mm;  < 0.00001) and left (96.67 mm 90.80 mm;  < 0.00001) sides. The reduction in left-side tract length for obese patients is significantly greater than that of normal weight patients (11.88 mm -5.02 mm;  = 0.001). The left kidney displaces ventrally (11.12 mm 18.59 mm;  < 0.00001), while the right kidney does not (14.26 mm 15.30 mm;  = 0.30). The right kidney displaces cranially (62.76 mm 79.51 mm;  < 0.00001), while the left kidney does not (64.35 mm 66.52 mm;  = 0.14). The left kidney in females moves medially, while no change is seen in males (4.22 mm -0.48 mm;  = 0.0004). The left kidney in females displaces toward the descending colon, while it moves farther away in males (2.73 mm -2.01 mm;  = 0.011). Both sex and body mass index had effects on the movement of the kidneys upon pronation. The differences can be clinically useful to help pre- and intraoperative planning.