During conventional LPN, renal artery clamping could provide good intraoperative visualization and bleeding control, but inevitably causes warm ischemia injury . Warm ischemia injury remains one of the most important factors influencing postoperative renal function during nephron sparing surgery. Several techniques have been developed to preserve better postoperative renal function, such as segmental artery clamping and thermal ablation techniques [13, 14].
The concept of zero-ischemia LPN was firstly introduced by Gill et al. . They tried to eliminate global renal ischemia by meticulous microdissection of tertiary or quaternary renal arterial branches feeding the tumor, which is based on the concept of anatomical renovascular microdissection . However, dissecting tumor feeding arteries from the renal hilum is technically difficult and time-consuming. Although off-clamp LPN has been developing and popularizing among the urologic communities [16, 17], the uncertainty of the intrarenal relationships of the tumor and feeding arteries makes off-clamp partial nephrectomy even more difficult. Therefore, preoperative understanding of the tumor and renal vascular anatomy is of great importance.
Preoperative CTA has been the preferred imaging modality for the evaluation of renal tumors in our hospital. With the development of CT and computer technology, it allows the generation of high quality images of the renal vasculature, tumor and collecting system at any plane . It can also facilitate establishing conventional 3D models to visualize the arterial vasculature within the hilum, guiding in choosing the appropriate hilar approach and intraoperative target orientation during segmental artery clamping . However, conventional CTA has a poor capacity to display the precise location and the precise anatomical interrelationship of various intrarenal tributaries, especially the tumor feeding arteries. Moreover, conventional 3D models based on CTA typically display kidney, renal vascular and tumor as opaque, which makes it impossible to visualize the intrarenal relationships between the tumor and its adjacent feeding arteries . As a well performed preoperative evaluation of the relevant intrarenal anatomy and intraoperative orientation of tumor feeding arteries is needed for zero-ischemia LPN, it is imperative to develop new techniques for radiologic guidance.
Conventional 3D CT reconstruction techniques typically present kidney, tumor and renal vessels as opaque, which makes it impossible to visualize the intrarenal relationships of the tumor and adjacent feeding arteries . In this study, the patients in the 3D group underwent 3D reconstruction. The reconstruction images included 3D surface rendered semitransparent renal tumor, transparent kidney, collecting system and 3D course of extra- and intrarenal tumor feeding arteries (Figure.1C-D). Therefore, the relationship between the tumor and collecting system, and the location and number of tumor feeding arteries were clarified much more easily. In addition, the use of 3D reconstruction of renovascular tumor resulted in more accurate dissection of target tumor feeding artery than in the CTA group during the operation, thus decreasing intraoperative OT and EBL.
When compared to conventional CTA, 3D reconstruction techniques have several advantages [20, 21]. Porpiglia et al. compared robotic partial nephrectomies performed with or without the use of hyper-accurated 3D reconstructions, concluding that it allowed for a faithful representation of the kidney arterial vasculature, which could lead to avoiding ischemia of the healthy renal remnant .
Similarly, Bertolo et al. compared 3D reconstructions with the standard imaging in the capability of expanding the indications to a nephron sparing surgery for very complex renal masses. More than 20% responders changed their indication from radical to partial nephrectomy after reviewing the 3D reconstruction and it might represent a significant step toward the validation of the use of 3D reconstruction for surgical planning in patients undergoing robotic kidney surgery .
In summary, based on our findings, we confirmed that 3D reconstruction techniques could clearly display the intrarenal arterial tree and the detailed anatomical relationships between the tumor, collecting system and intrarenal arteries. The reconstructed images can also be rotated to clarify the number and location of tumor feeding arteries. It can not only provide reference for the preoperative evaluation and determination of appropriate dissection strategy, but also for the intraoperative orientation, therefore avoiding invisible injury to other interlobar arteries during zero-ischemia LPN.
There were also several limitations in this study. First, this was a single-center retrospective study with small sample size and patients received only short-term follow up, the evaluation of long-term outcomes is still awaited. Second, the median tumor size was 4.0 and 3.75 cm in each subgroup, whether this approach is also applicable in the management of larger T1b renal tumors is still unclear. Robot assisted zero-ischemia partial nephrectomy may be helpful for better tumor resection, renorrhaphy and renal function preservation in the management of T1b or even complicated renal tumors [4,22], but our experience is also lacking in this field. Third, the 3D reconstruction technique based on CT images is not applicable to magnetic resonance imaging. Thus, patients who cannot receive enhanced CT or CTA are excluded from the study. Although the tumor feeding arteries were confirmed more accurately under the guidance of 3D reconstruction technique, the rate of accurately tumor feeding arteries orientation was only 91.7%, without statistical significance as compared with conventional CTA technique.