Querying the significance of patient position during computerized tomography on the reliability of pre-percutaneous nephrolithotomy planning

Background: Computerized tomography (CT) is considered indispensable in percutaneous nephrolithotomy (PCNL) planning. We aimed to define the reliability of pre-PCNL CT for planning renal access by assessing renal positional changes between supine and prone CTs. Subjects and methods: CT urographies (CTU) of 30 consecutive patients were reviewed for distances upper pole (UP)–diaphragm, UP–diaphragm attachment, renal pelvis (RP)–lateral body wall, RP- posterior body wall, and lower pole (LP)- anterior–superior iliac spine (ASIS). The posterior and lateral renal axes angles were also calculated. Results: The most consistent overall movement in transition from prone to supine was backward rotation, as demonstrated by a decrease in distance UP–posterior body wall (p = 0.010) and increase in the posterior renal angle (p < 0.0001). This finding correlated with the patient’s body mass index (BMI) (p = 0.029). The left kidney was more mobile than the right one, moving significantly for five of the measured parameters compared to the right kidney which moved significantly for only two parameters. The UP-diaphragm distance of the left kidney correlated with age (p = 0.014), the RP-lateral wall distance correlated with previous abdominal surgery (p = 0.006), and the RP-posterior wall distance with BMI (p = 0.017). On the right, the UP-diaphragm distance correlated with gender (p = 0.002) and the lateral renal rotation was smaller (p = 0.046). Conclusions: Kidneys present significant mobility between supine and prone positions. CT assessment should be performed in the position expected during surgery and should be interpreted with caution, while a real-time imaging modality should be used in the operating room.