Association of clinical and radiographic features with perinephric "sticky" fat.

Background and Purpose: The discovery of thick, adherent, perinephric sticky fat (PSF) is relatively common during open or laparoscopic retroperitoneal surgery. To our knowledge, however, there has been no previous analysis of clinical or radiographic features associated with the development of PSF or of perioperative outcomes for those patients in whom it is found. Our objective is to analyze potential predictive features and determine whether there is any effect on clinical or pathologic outcomes for patients with perinephric sticky fat. Patients and Methods: Patients undergoing partial nephrectomy or laparoscopic cryoablation with available preoperative imaging were identified from 2005 to 2011. Operative records were reviewed to identify patients with and without PSF. Preoperative images and medical records were examined to obtain patient data regarding potential predictors as well as clinical and pathologic outcomes. Results: A total of 29 patients were identified-16 with PSF and 13 controls. Statistically significant factors associated with PSF included sex, tumor size, presence of perinephric stranding, tumor >50% exophytic, and thickness of perinephric fat (P < 0.05). Median total operative time for patients with sticky fat was nearly 40 minutes longer than the control group (228 min vs 190 min, P < 0.05). All four (17%) patients with Fuhrman grade 3 or 4 renal-cell carcinoma were from the sticky fat group (P = 0.09). Conclusions: Despite the small sample size, multiple possible factors associated with perinephric sticky fat were identified and may provide guidance for future investigation of this phenomenon.