European Urology

Over the last decade we have witnessed a plethora of scientific work regarding renal functional preservation in the setting of a renal mass. This topic has become increasingly important for a couple of reasons: Decreased renal function has been associated with diminished survival and increased morbidity in the general medical population [1], and partial nephrectomy (PN) has equivalent cancer control compared with radical nephrectomy (RN) and better preserves renal function [2].

A hypothesis arose suggesting that renal function preservation associated with PN might be associated with better survival in patients with renal masses. Initial comparisons of cohorts of patients treated by either RN or PN did show improved survival for those treated by PN [3] and [4], but in these nonrandomized cohorts, it was unclear whether this result was merely due to selection bias or other confounding variables. In a recently reported randomized trial comparing PN and RN, a survival advantage was not observed for PN; however, glomerular filtration rates (GFRs) were not reported, and the study was closed due to poor accrual after 541 of the planned 1300 patients were accrued [5].

If the theory holds, the mere act of performing a PN is beneficial only in so much as it preserves renal function. This idea was underscored by a recently published cohort of 1004 patients with cT1b renal masses [6]. In this propensity score analysis of overall survival controlling for tumor size, age, comorbidities, and preoperative renal function, PN was associated with improved overall survival. However, if postoperative renal function was included in the same model, then only postoperative renal function was predictive and PN was no longer independently associated with overall survival. PN appears to be associated with improved survival, as compared with RN, but this association is dependent on preservation of renal function.

With the rising importance of renal function preservation in renal surgery, several investigators have set out to determine what factors are most important in predicting postoperative renal function. One such factor that is potentially modifiable from a surgical standpoint is the duration of ischemia time, which has been observed to be associated with short- and long-term renal function after PN (reference 11 in Ng et al [7]). In this capacity, many have worked to reduce ischemia time by early unclamping (reference 8 in Ng et al [7]), whereas we and others have observed improved renal function after PN without the use of hilar clamping [8].

In this issue of the Platinum Journal, a novel technique called zero ischemia is reported from the University of Southern California [7]. This captivating new technique attempts to limit postoperative renal functional loss by meticulous preoperative planning using ultrathin 0.5-cm-slice computed tomography scans with three-dimensional reconstruction. The surgeon proceeds to dissect from the hilum toward the tumor, superselectively controlling blood vessels going to the tumor, excising the tumor, and using real-time intraoperative monitoring of the remaining normal kidney to ensure adequate blood flow.

Putting the issue of technical difficulty aside, does this new technique offer any measurable advantage over traditional PN techniques? Further follow-up and additional observations are needed to answer this question. Nevertheless, in the initial postoperative period, the renal function decline associated with the zero ischemia technique, with or without vascular microdissection, does not appear to be much different from the standard technique [7]. The authors report the median loss in estimated GFR to be around 10–11 ml/min per 1.73 m² at 2 mo. This decrease is quite comparable to the reported drop observed with traditional PN [9]. Although the authors remain optimistic that most robotic surgeons could adopt such a technique [7], such vascular dissection with the risks of vascular injury would certainly preclude many from attempting the procedure and, at least initially, should be limited to surgeons with extensive surgical experience.

We commend the authors for developing a surgical approach that attempts to minimize the ischemic insult associated with renal hilar clamping. Although minimizing ischemia is an important modifiable feature during PN, it should be noted that the quality and quantity of preserved vascularized kidney appears to be the driving force of ultimate renal function after PN [10]. Nevertheless, renal function preservation continues to be a dynamic area of research and debate, and we await further results to determine whether this novel technique will provide a measurable advantage for the patient.

Conflicts of interest

The authors have nothing to disclose.