Predicting ease of perinephric fat dissection at time of open partial nephrectomy using preoperative fat density characteristics

Abstract

ObjectiveTo predict the ease of perinephric fat surgical dissection at the time of open partial nephrectomy (OPN) using perinepheric fat density characteristics as measured on preoperative computed tomography (CT). Patients and MethodsIn all, 41 consecutive OPN patients with available preoperative imaging and prospectively collected dissection difficulty assessment were identified. Using a scoring system that was adopted for the purposes of this study, the genitourinary surgeon quantified the difficulty of the perinephric fat dissection on the surface of the renal capsule at the time of surgery. On axial CT slice centred on the renal hilum, we measured the quantity and density of perinephric fat whose absorption coefficient was between -190 to -30 Hounsfield units. Correlation between perinephric fat surface density (PnFSD) as noted on preoperative imaging and as observed by the surgeon at time of surgery were correlated in a completely 'double-blinded' fashion. Density comparisons between fat dissection difficulties were made using an ANOVA. Associations between covariates and perinephric fat density were evaluated by univariate and multivariate logistic regression analyses. Receiver-operating characteristic (ROC) curves for six different predictive models were created to visualise the predictive enhancement of PnFSD. ResultsPnFSD was positively correlated with total surgical duration (Pearson's correlation coefficient 0.314, P = 0.04). PnFSD significantly correlated with gender (P = 0.001) and difficulty of perinephric fat surgical dissection (P < 0.001) scores. The mean (SD) PnFSD for a dissection that was not difficult (n = 19) was 5598.32 (1367.77) surface density pixel unit (SDPU), and for a difficult dissection (n = 22) was 10272.23 (3804.67) SDPU. Univariate analysis showed gender (P = 0.002), and PnFSD were predictive of the presence of 'sticky' perinephric fat. A multivariate analysis model showed that PnFSD was the only variable that remained an independent predictor of perinephric fat dissection difficulty (P = 0.01). Of the six ROC models assessed, only PnFSD had a significant capability to predict the difficulty of the perinephric fat dissection due to the presence of highly adherent 'sticky' fat, with an area under the curve of 0.87 (P < 0.001). ConclusionAccurate preoperative assessment of perinephric fat density constitutes a strong indicator of perioperative fat dissection difficulty. Perinephric fat densities can be practically obtained from preoperative CT to identify 'sticky' fat, which may help determine the anticipated ease of surgical dissection, which can guide education, preoperative surgical planning, and potentially the surgical approach offered to patients.

Adherent Perinephric Fat in Asian Patients: Predictors and Impact on Perioperative Outcomes of Partial Nephrectomy

“…The incidence of APF in our study was 17%, which was lower than the incidence rates in previous studies of Western cohorts (30-55%) [3,4,6,13]. BMI was associated with APF in this Asian cohort as it was in the Western cohorts, although the mean BMI (24 kg/m 2 ) in our study was smaller than those in Western studies (29-33 kg/m 2 ) [5,6,12]. Since Asians tend to have higher percentages of body fat than Caucasians do at equivalent BMIs [7,8], it could be supposed that the incidence of APF in Asians is close to that in Caucasians, in spite of the difference in their mean BMIs.…”

“…In other studies, radiographic features have been said to be independent predictors of APF [12,13]. The MAP score has broad utility because it can be calculated based on both computed tomography and T1-weighted magnetic resonance imaging [6].…”

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

“…APF can be a frustrating surgical variable encountered during PN that can limit mobilization of the kidney and isolation of the kidney tumor, and its removal can often lead to tearing of the renal capsule [14]. Experienced and respected partial nephrectomists have openly commented on the need for a model that predicts the risk of encountering intraoperative APF [7].…”

“…Therefore, we did not include an analysis of the impact of APF on the outcomes of RAPN. In the only studies thus far examining APF along with operating room variables, APF was shown to predict longer operating room times for PN [14,19]. APF alone may be a surrogate for surgical complexity and may push less experienced partial nephrectomists to select an alternative approach, such as an open PN or an ablation, for treating small renal masses in these particular patients.…”

“…APF was present in 30% of the RAPN in this series. The true incidence of APF encountered during PN is difficult to determine due to limited data, and the only two assessments in the literature of APF encountered during PN note that 53.7% [14] and 55.2% [19] of patients had APF. The true rate of APF encountered during PN will need to be elucidated in larger series.…”