Adherent perinephric fat at minimally invasive partial nephrectomy is associated with adverse peri-operative outcomes and malignant renal histology

Objectives To predict adherent perinephric fat (APF) at minimally invasive partial nephrectomy (MIPN) using the Mayo adhesive probability (MAP) score and to determine the impact of MAP score and APF on MIPN outcomes. Patients and Methods A total of 245 patients undergoing MIPN were included in the study. The presence of APF was determined through keywords in operating notes, and radiographic data were obtained from preoperative cross-sectional imaging. Posterior fat thickness was measured between the renal capsule and the posterior abdominal wall at the level of the renal vein. Perinephric stranding was graded on a 0-3 severity scale. Results The study included 123 men and 122 women, with a median age of 55 years, body mass index of 31.7, tumour size of 2.7 cm and nephrometry score of 6. The median posterior fat thickness was 1.79 cm and MAP score 2.63. In all, 26 patients (10.6%) had evidence of APF at the time of renal surgery. Factors predictive of APF included increasing age (P = 0.001), male gender (P = 0.045), perinephric stranding (P = 0.002), posterior fat thickness (P < 0.001) and MAP score (P < 0.001). APF was associated with adverse pathological and peri-operative outcomes including malignant renal histology (P = 0.04), longer operating time (P = 0.005) and greater estimated blood loss (EBL; P = 0.025). Conclusions Specific clinical and radiographic factors predict APF at MIPN. The presence of APF is associated with adverse peri-operative outcomes including longer operating time and greater EBL. APF was also associated with renal malignancy on final pathology, but further studies are necessary to elucidate the precise underlying mechanism.