With the development of image diagnosis techniques and the larger number of exams requested, the incidence of small renal tumors has increased as well as the indication for nephron-sparing surgery, with excellent oncological and functional outcomes [1] . Incidental lesions account for more than 60% of the renal tumors detected [2] .

Partial nephrectomy is being increasingly used for small renal masses (<4 cm) and, in selected cases, up to 7 cm renal tumors, with similar outcomes compared to radical nephrectomy [3] [4] [5] .

Completely intraparenchymal renal tumors imply greater technical difficulties for location and resection, which may increase the chances for complications [6] . The exact location of the tumor during surgical resection is provided by intraoperative ultrasonography [7] .

Currently, despite the group’s experience in open partial nephrectomy, including removal of intraparenchymal tumors [8] , there is a natural transition towards minimally invasive techniques [9] , the robotic one in particular [10] (Figure 1).

This study aims to present a robot-assisted surgical approach for the removal of completely intraparenchymal renal tumors.

We retrospectively analyzed 13 patients undergoing RAPN, all with completely endophytic tumors. Patient demographics, perioperative, functional and oncological outcomes were assessed. All patients underwent RAPN between August/2016 and July/2021 by a single senior surgeon (MFD), with large previous experience in open partial nephrectomy, including cases of intraparenchymal tumors. This retrospective study had been approved by Institutional Ethical Committee, the formal consent was not required because the images are anonymous from which the individual cannot be identified.

The detailed surgical technique is described below:

1) The transperitoneal approach for RAPN was followed in all cases.

2) Access was gained through four robotic trocar positions, the kidney was dissected and exposed, and the renal artery was clamped;

3) Ultrasound was used to identify the tumor margins and depth. Before the renal hilum was clamped, 12.5 g and 20% manitol was administered for nephron protection during warm ischemia.

4) Shortly after the renal artery was clamped with a bulldog clamp, nephrotomy was performed on a marked area aided by the US. Tumor enucleation was then performed by using a bipolar fenestrated grasper and a blunt and sharp dissection Scisor.

The surgical specimen was promptly forwarded for histopathological analysis of the margins during renal reconstruction (Figure 2). Hemostasis was done with 2.0 v-lock parenchymal suture. The kidney was then sutured using Vicryl 0 running suture;

5) In all cases a suction drain was placed around the gerota fascia.

In a total of thirteen patients assessed, the mean age was 52 years, all being males. The mean tumor size was 2.6 cm, with a mean 24 min warm ischemia time. Mean preoperative serum creatinine was 0.9 mg/dl and the postoperative value was 1.0 mg/dl (Table 1 and Table 2).

Histopathological analysis showed only one lesion of benign etiology, and among the renal cell carcinomas, eight were clear cells and four were papillary (Table 3). Most were low Fuhrman grade lesions and no positive surgical margins were found in this series (Table 4 and Table 5).

None of the patients had significant intraoperative bleeding, required any blood transfusion or evolved to fistulae or urinary collections in the postoperative. None of the patients undergoing the surgery had any renal function unit loss.

All the patients were monitored under the same protocol during a mean 36-month (6 - 72) follow-up, and no local recurrence or systemic diseases were observed.

Robotic nephrotomy in the handling of solid and completely endophytic tumors represents a definitive and reliable approach, preserving renal function in all cases, besides providing a better exposure and safety for tumor resection. The robotic surgery advantages and the growing experience in nephron-sparing minimally invasive surgeries enable experienced surgeons to perform RPN in challenging cases [11] .

Rogers et al. [12] were the first to show the feasibility and safety of RAPN in twelve complex cases, including hilar, endophytic, and/or multiple tumors. The mean size of the tumor was 3.6 cm, with 192 min mean operative time and 31 min WIT. All patients had negative surgical margins. Later, Gong et al. [13] reported the results of 29 patients undergoing RAPN for renal mass, including hilar, endophytic, and multiple tumors. The mean size of the tumor was 3 cm, with 197 min mean operative time and 25 min WIT. All cases had negative surgical margins and no recurrence was found in the mean 15 months follow-up.

Compared to such historical series, our findings suggest excellent RAPN performance for completely endophytic masses. Our group reported the consecutive experience in 13 cases, with mean 2.6 cm tumor size, mean 150 min operative time, and 24 min WIT. A small rate of intraoperative complications was evidenced, all surgical margins were negative, and no recurrence was found after a 36-month follow-up.

Besides, the achievement of a “Trifecta” that stands for a parameter introduced to define the quality of the RAPN procedure [14] , in 69% of the endophytic tumors, shows a favorable outcome compared to other minimally invasive PN series reported [15] [16] .

Partial nephrectomy and/or enucleation account for 30% of the surgical procedures in the treatment of renal tumors, with survival similar to the one found in radical nephrectomy for the early stages, evidencing a cancer-specific and overall survival of 98% and 97%, respectively [1] [4] . For <4 cm tumors, no additional surgical margin needs to be removed for ideal cancer control. The study reaffirmed the relevance of the healthy parenchyma thickness excised along with the tumor for long-term renal function preservation. Simmons et al. [17] showed the percentage of renal volume preservation rather than WIT to be the main determinant of the final eGFR following PN, and that the technical changes designed to minimize healthy volume loss, while still reaching negative margins, may account for a better functional outcome.

There are many definitions of central tumors, the best accepted of which are those of Black et al. [18] , when the lesion is fully surrounded by normal renal tissue, and that of Brown et al. [19] , when the lesion is less than 5 mm distant from the excretory system or hilar vessels. A rather challenging scenario is represented by such completely intraparenchymal renal masses, considering that the surgeon has no visual clues of the tumor location as the kidney surface is reached. Thus, surgical removal of those lesions encompassed greater technical difficulties for location and resection, besides a greater probability of perioperative complications. If well-succeeded perioperative and oncological outcomes are to be achieved, we strongly suggest that intraoperative ultrasound be used for identification of tumor margins, as advocated by Assimos et al. [20] . It can be controlled robotically or laparoscopically by the bedside assistant.

The use of minimally invasive ablative therapies, such as radiofrequency and cryotherapy for small renal tumors, is currently on the rise, providing greater safety and broadening their indications [21] However, since the tumor is endophytic and close to the excretory path and hilar vessels, this approach may be a limiting factor [22] . A nephron sparing surgery for central tumors has shown to be safe and effective compared to peripheral tumors, evidencing that operative and ischemia time, the need to close the collector system and blood transfusion showed no statically significant differences. Autorino et al. [23] reported their experience in the robotic management of renal mass, comparing the results of endophytic masses with mesophytic and exophytic tumors and stated that they found no differences in terms of surgical complications, positive margins rate or postoperative changes in eGFR.

The limitations of this study involve its retrospective nature despite the prospective data collection, the small number of patients, 36-month median follow-up, and absence of studies of the renal function of the units treated, or of serum creatinine. Nevertheless, the lesions were safely enucleated, providing negative margins and an acceptable warm ischemia time.

As a positive point, it seeks to encourage that the robotic approach be performed, even by surgeons with small or no experience at all in laparoscopic surgery.

RAPN can be performed safely and effectively for endophytic renal tumors. The accurate use of laparoscopic US and the exclusive robotic surgery platform resources facilitate the procedure in this challenging scenario.

The data are stored in the electronic medical record system of the Hospital.

The authors declare no conflicts of interest regarding the publication of this paper.

Dall’Oglio, M., Paiva, M.M., Kaminagakura, F.G., da Silva Júnior, J.A.F. and Ocké, J. (2023) Robot-Assisted Nephrotomy as a Nephron-Sparing Approach for Completely Intraparenchymal Renal Tumors. Open Journal of Urology, 13, 459-467. https://doi.org/10.4236/oju.2023.1310052