Is There a Role for Prone Computed Tomography Before Percutaneous Nephrolithotomy?

The majority of percutaneous nephrolithotomies (PCNLs) are performed prone, whereas most preoperative CT scans are done supine. The purpose of this pilot study is to determine if there is utility of prone CT scans in preoperative planning for prone PCNL by identifying patient populations at risk for organ injury and tract length-related complications. To represent typical preoperative planning using CT, two-dimensional (2D)-axial-prone/supine percutaneous tract measurements were performed by minimizing the distance from the target calix to the posterior-lateral skin in a single axial plane. The minimum distance and organ interception rates for the 2D-axial planning scans were recorded. A total of 60 CT colonography and 13 CT urography patients were included in analysis. There were 42 women and 31 men with unspecified pathology reports ranging in age from 27 to 86 years and in body mass index (BMI) from 17.1 to 49. Multiple logistic regression identified female gender and low BMI as predictors of organ interception on the left. On multiple linear regression comparing the difference in axial prone/supine lengths; BMI, gender, and age were not significant independent predictors of changes in tract length in any pole when prone supine. However, shorter supine tracts tended to lengthen when prone, and longer supine tracts tended to shorten. This pilot study has demonstrated that patients with long and short estimates of tract length in the supine position may have shorter and longer tracts, respectively, with repositioning to prone. Thus, prone CT may have benefit when anticipating exceptionally long (>15 cm) tract lengths. Prone scans also revealed more potential organ interceptions, particularly for low BMI and women in the left upper pole. In patients for whom prone CT demonstrates an organ interception, the urologist should consider an alternate target calix or ultrasound-guided percutaneous access to identify the most appropriate needle trajectory.