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Anthropometric Renal Anatomic Alterations Between Supine and Prone Positions in Percutaneous Renal Ablation for Renal Cortical Neoplasms.

OBJECTIVES
To establish patterns of anatomic changes relevant to the kidney and colon during positional change between the supine and prone positions as noted on CT scans performed during percutaneous cryoablation for renal cortical neoplasms (RCN).


METHODS
Nineteen patients undergoing percutaneous cryoablation for RCN with abdominal CT scan in both the supine and prone positions were included in the study. We documented the anterior/posterior, medial/lateral, and cranial/caudal anatomic changes of the kidney, kidney rotation, and the proportion of the kidney whose access was limited by the liver, spleen, and lung. We also calculated the length of the percutaneous access tract and the distance between the colon and kidney in hilar position as well as the anterior/posterior location of the colon relative to the kidney.


RESULTS
In the prone position, the kidney lies significantly more anteriorly on both sides: 4.7 cm vs 4.3 cm (L) and 4.4 cm vs 4.1 cm (R) (p = 0.02 and p = 0.03, respectively). On prone CT images, both kidneys are more cranial when compared with the supine position: 80.4 mm vs 60.8 mm (L) and 87.2 mm vs 57.4 mm (R) (p = 0.002 and p < 0.001, respectively). The skin to tumor distance is significantly shorter in the prone position (p < 0.0001 [L], p = 0.005 [R]). The colon lies closer to the hilum of the kidney and is more posteriorly located in the prone position: 1.21 cm vs 1.04 cm (L) and 0.80 cm vs 0.70 cm (R) (p = 0.005 and p = 0.005, respectively). In the prone position, the lung covers a significantly larger proportion of the right kidney (27.3 mm vs 6.05 mm, p = 0.0001).


CONCLUSIONS
We documented clinically significant anatomic alterations between supine and prone CT imaging. The changes associated with the prone position modify percutaneous access, particularly for right upper pole tumors. Prone imaging before surgery may be helpful in selected cases.