Mayo Adhesive Probability Score: An Accurate Image-based Scoring System to Predict Adherent Perinephric Fat in Partial Nephrectomy

BackgroundImage-based renal morphometry scoring systems are used to predict the potential difficulty of partial nephrectomy (PN), but they are centered entirely on tumor-specific factors and neglect other patient-specific factors that may complicate the technical aspects of PN. Adherent perinephric fat (APF) is one such factor known to make PN difficult.ObjectiveTo develop an accurate image-based nephrometry scoring system to predict the presence of APF encountered during robot-assisted partial nephrectomy (RAPN).Design, setting, and participantsWe prospectively analyzed 100 consecutive RAPNs performed by one surgeon and defined APF as the need for subcapsular renal dissection to isolate the renal tumor for RAPN.Outcome measurements and statistical analysisThe scoring algorithm to predict the presence of APF was developed with a multivariable logistic regression model using a forward selection approach with a focus on improvement in the area under the receiver operating characteristic curve.Results and limitationsThirty patients (30%; 95% confidence interval, 21-40) had APF. Single-variable analysis noted an increased likelihood of APF in male patients (p < 0.001), higher body mass index (p = 0.003), greater posterior perinephric fat thickness (p < 0.001), greater lateral perinephric fat thickness (p < 0.001), and those with perirenal fat stranding (p < 0.001). Two of these variables, posterior perinephric fat thickness and stranding, were most highly predictive of APF in multivariable analysis and were therefore used to create a risk score, termed Mayo Adhesive Probability (MAP) and ranging from 0 to 5, to predict the presence of APF. We observed APF in 6% of patients with a MAP score of 0, 16% with a score of 1, 31% with a score of 2, 73% with a score of 3-4, and 100% of patients with a score of 5.ConclusionsMAP score accurately predicts the presence of APF in patients undergoing RAPN. Prospective validation of the MAP score is required.Patient summaryThe Mayo Adhesive Probability score that we we developed is an accurate system that predicts whether or not adherent perinephric, or “sticky,” fat is present around the kidney that would make partial nephrectomy difficult.