Introduction:

The surrounding anatomy of a renal mass may complicate partial nephrectomy (PN). Visceral obesity and adherent perinephric fat (APF) have been linked to worse perioperative outcomes and higher rates of malignancy. Body mass index (BMI), which fails to distinguish between visceral and subcutaneous fat, does not capture patient-specific fat factors that complicate PN. The Mayo Adhesive Probability (MAP) score is an image-based scoring system developed to predict APF preoperatively and aid in surgical planning. With the increasing capabilities of imaging software, other investigators have proposed quantifying the visceral obesity encountered during PN as an alternative to BMI (figure 1). The objectives of this prospective observational study were to compare relevant fat measures and assess their impact on perioperative outcomes. We also aimed to prospectively validate the MAP score at our institution.

Methods:

With IRB approval, between August 2018 and March 2020, patients undergoing robotic PN were consented for the study. The fat parameters we evaluated included visceral (VF) and subcutaneous fat (SF) area and volume, BMI and MAP score. VF and SF were quantified using TeraRecon (v4.4.13) analysis of preoperative imaging. VF ratios were calculated as VF/(VF + SF). VF volume boundaries were set from the most superior aspect of the kidney to the insertion of the psoas and VF area was determined at the level of the renal hilum (figure 1). Intraoperatively, the surgeon assessed the presence of APF. The MAP score was evaluated independently of the intraoperative APF assessment as described by Daviduk et al. Our patient population was then analyzed as two groups: patients with APF and patients without APF intraoperatively. We evaluated the correlation amongst different fat measures and assessed the relationship between APF and perioperative outcomes.

Results:

Of the 139 patients that underwent a robotic PN and consented for the study, 47 (34%) had APF (+APF). Demographic, fat, tumor, surgical and perioperative characteristics are included in table 1. The +APF patients were predominantly older males with multiple medical comorbidities. There was no statistically significant difference in BMI between the +APF and ∅APF groups (29 vs 27 kg/m²; p=0.19), but the +APF group had more VF and higher MAP scores (4 vs 1; p<0.01). All fat measures except for BMI were highly correlated (ρ>0.7). With increasing MAP score, VF ratio increased linearly, whereas BMI was relatively unchanged. On receiver operating characteristic analysis, at the optimal threshold of MAP≥4 to predict APF, a sensitivity of 0.81 and specificity of 0.78 were observed in our cohort. +APF patients had higher EBL and longer operative times (p<0.01), but higher complication and malignancy on final pathology rates were not observed. 

Conclusion:

Alternatives to BMI that distinguish VF from SF capture patient-specific fat factors that complicate PN. VF ratios and MAP score are highly correlated. These measures of visceral obesity provide information about perioperative outcomes that is not captured by nephrometry scores centered on tumor-specific factors. Visceral obesity measures should be used in preoperative counseling and surgical planning for PN.

Funding: NA