In robot-assisted radical prostatectomy (RARP), nerve-sparing (NS)  procedures are considered crucial step not only for improving postoperative sexual function but also for achieving early urinary continence, and improving lower urinary tract symptoms(LUTS). Since a cavernous nerves cannot be directly visualized during surgery, a landmark-based approach using the prostatic fascia and vessels coursing along the prostate is adopted for NS technique. However, even if one assumes separation between the nerves and the prostatic fascia to perform NS procedures, there are instances where the separation has progressed within the prostate, leading to possibility of the results of positive surgical margins. The difficulty in identifying the separation line is presumed to be due to individual differences in prostate morphology, the prostate size, the presence or absence of median lobe hypertrophy, prostate hardness, and so on. Therefore, mastering NS RARP requires experience with a substantial number of cases. Consequently, there is a need for the development of NS surgical techniques that are safe and reliably applicable, even for less-experienced surgeons. In this context, we have developed of a high-precision nerve-sparing surgical method using the indocyanine green (ICG) fluorescence navigation system. The ICG fluorescence navigation system utilizes the property that ICG fluoresces when exposed to specific excitation light. This system allows the observation of blood flow distribution. Therefore, by administering ICG before the NS procedure, the boundary between the neurovascular plate containing the neurovascular bundles (NVBs) and the prostatic fascia became clearly visible. This system for visualizing ICG is standard equipment on the da Vinci Xi system. The aim of the present study is to identify the efficacy of our developed NS RARP through subjective and objective data.

This prospective clinical cohort study targeted a consecutive group of 43 patients who underwent NS RARP at our institution between April 2019 and April 2021. The patient cohort was divided into two groups for investigating the impact of ICG administration on NVBs: 23 cases in the ICG-administered group (ICG group) and 20 cases in the non-administered group (non-ICG group). In the ICG group, after 5mg administration of ICG, NS was performed. (fig 1) The primary outcome measure is to compare the residual nerves in prostate specimens between the ICG group and the non-ICG group in order to the surgical quality of the NS procedures. Secondary outcome measures were to compare postoperative erectile function, LUTS, lower urinary tract function, urinary incontinence between the two groups.
To evaluate the residual nerves in the prostate specimens, pathological examinations was performed for collecting slides from three regions (apex, middle, and base) of prostatectomy specimens from 43 cases. Immunohistochemical staining with the nNOS antibody was performed to evaluate the residual nerves. The number of nNOS-positive nerve cells was counted in the base, middle, and apex. (fig 2) A smaller number of nNOS-positive nerve cells in pathological specimens indicates that more nerve cells are preserved within the body.
Erectile function was assessed by measuring the Sexual Health Inventory for Men (SHIM) score, a patient-reported outcome associated with erectile dysfunction. LUTS were evaluated using the International Prostate Symptom Score (IPSS) and the Quality of Life (QOL) index. Additionally, IPSS each score, i.e. post-void residual sensation, frequency, intermittency, urgency, weak stream, straining, and nocturnal frequency, was assessed. Lower urinary tract function was assessed by determining the maximum flow rate using uroflowmetry (UFM) and evaluating the post-void residual urine volume (PVR) determined by ultrasound examination. These parameters were evaluated at the outpatient clinic one month after the surgery. Urinary incontinence was evaluated by calculating the incontinence rate, which is the amount of urinary leakage divided by the total daily urine volume on the day following removal of the urethral catheter 5 or 7 days after RARP.

There was no significant difference observed between the two groups in terms of the age, surgical time, blood loss, or positive surgical margin. The number of nNOS-postive cells of the apex in the IGC group and non-ICG group were 10.0 ±4.6 and 7.9 ±7.1, P=0.96, respectively. The number of n-NOS-positive cells of midsection in the IGC group and non-ICG group were 8.1 ±7.4 and 12.5 ±9.1, P=0.24, respectively. The number of n-NOS-positive cells of base in the ICG group and non-ICG group were 15.0 ± 6.9 and 26.9 ± 21.4, P=0.02, respectively. Thus, in the ICG group, significant decrease of n-NOS-positive cells were only observed in the base of the prostate. (fig3)
In terms of postoperative erectile function, there was no significant difference in postoperative SHIM scores between the ICG group and the non-ICG group (ICG group: non-ICG group = 1.7 ±1.1 and 2.0 ±1.6 P=0.53). Regarding LUTS, while there was no significant postoperative improvement in the non-ICG group based on the IPSS total score, a significant improvement was observed in the ICG group (13.6 ±4.9 to 8.7 ±5.0, P = 0.02). In addition, in the ICG group, significant improvements were observed in the sub-scores for voiding symptoms, such as urinary hesitancy (IPSS 3) (1.7 ±1.6 to 0.6 ±0.7, P = 0.01) and weak stream (IPSS 5) (1.7 ±1.5 to 0.5 ±0.9, P = 0.01). However, there were no significant improvements in other sub-scores and QOL index between the two groups. Regarding lower urinary tract function, there were no significant differences between the two groups in the UFM parameters of maximum flow rate (P=0.23) and PVR (P=0.07). The incidence of urinary incontinence also showed no significant difference between the two groups (P=0.16).

In this study, intravenous administration of ICG was shown to significantly reduce the presence of residual nerves in the base of the prostate. The use of ICG enabled a clearer visualization of the boundary between the prostatic capsule and surrounding tissues, allowing for more precise anatomical dissection during surgery. This suggests that ICG may enhance surgical quality, particularly contributing to nerve preservation in the base region. Regarding postoperative erectile function, no significant difference was observed between the ICG group and the non-ICG group. 
However, significant improvement in LUTS was observed in the ICG group, particularly in sub-scores related to weak urinary stream and intermittent urine flow in IPSS. These results suggest that NS techniques using ICG may contribute to the improvement of LUTS.

Our innovative approach, which enhances the visualization of prostatic boundaries, suggests the potential for reliable and straightforward NS procedures, leading to a significant improvement in LUTS.