Efficacy of first-generation Cavermap to verify location and function of cavernous nerves during radical prostatectomy: a multi-institutional evaluation by experienced surgeons

Intraoperative Fluorescent Image Guidance for Nerve-Sparing Prostatectomy: A Review of Historical Context and Current Research

Fluorescent probes in the near-infrared (NIR) range have immense potential to improve observation of positive margins, lymph nodes, and nerves in prostatectomy. Development of fluorescent dyes and mechanisms of cellular uptake paved the way for the current emerging technologies. However, intracellular transport of fluorophores proved to be logistically challenging with respect to intraoperative deployment. Peptide-based probes with high specificity for nerves enabled broader and more rapid labeling. Key features of the ideal probe include selectivity, minimal background noise, safety, and low cost. Human neuropeptide 401 (HNP401) and oxazine-based probes perform well in these categories. As for tumor-specific labeling, prostate specific membrane antigen is relatively selective for the prostate and can be conjugated to a fluorophore. NIR spectrum emission is an ideal range for clinical imaging use, as fluorescence occurs outside the field of visible light, and tissue optical properties diverge significantly at the visible-NIR transition. Indocyanine, carbocyanine, and fluorescein derivatives are common fluorophore conjugates for the probes. Finally, to harness the power of fluorescence intraoperatively, the surgeon must look through a specialized lens. Multiphoton microscopy, optical coherence tomography, and confocal laser endomicroscopy have emerged as frontrunners in this arena. As with any evolving technology, ongoing research is expanding the applications of fluorescent intraoperative imaging in prostate surgery. Innovations in camera technology, dye selection, and image processing are refining the technique's capabilities. A core challenge of these technologies translating into the operating room relates to size and the ability to view objects at vastly different magnifications. Dual modality zoom settings are promising solutions. Furthermore, interdisciplinary collaboration between surgeons, imaging specialists, and researchers continues to drive advancements. In conclusion, fluorescent intraoperative imaging has the potential to usher in a new era of precision and safety in prostate surgery.

Cavernous nerve mapping methods for radical prostatectomy

INTRODUCTION

Preserving the cavernous nerves, the main autonomic nerve supply of the penis, is a major challenge of radical prostatectomy. Cavernous nerve injury during radical prostatectomy predominantly accounts for post-radical prostatectomy erectile dysfunction. The cavernous nerve is a bilateral structure that branches in a weblike distribution over the prostate surface and varies anatomically in individuals, such that standard nerve-sparing methods do not sufficiently sustain penile erection ability. As a consequence, researchers have focused on developing personalized cavernous nerve mapping methods applied to the surgical procedure aiming to improve postoperative sexual function outcomes.

OBJECTIVES

We provide an updated overview of preclinical and clinical data of cavernous nerve mapping methods, emphasizing their strengths, limitations, and future directions.

METHODS

A literature review was performed via Scopus, PubMed, and Google Scholar for studies that describe cavernous nerve mapping/localization.

RESULTS

Several cavernous nerve mapping methods have been investigated based on various properties of the nerve structures including stimulation techniques, spectroscopy/imaging techniques, and assorted combinations of these methods. More recent methods have portrayed the course of the main cavernous nerve as well as its branches based on real-time mapping, high-resolution imaging, and functional imaging. However, each of these methods has distinctive limitations, including low spatial accuracy, lack of standardization for stimulation and response measurement, superficial imaging depth, toxicity risk, and lack of suitability for intraoperative use.

CONCLUSION

While various cavernous nerve mapping methods have provided improvements in identification and preservation of the cavernous nerve during radical prostatectomy, no method has been implemented in clinical practice due to their distinctive limitations. To overcome the limitations of existing cavernous nerve mapping methods, the development of new imaging techniques and mapping methods is in progress. There is a need for further research in this area to improve sexual function outcomes and quality of life after radical prostatectomy.

Comprehensive approach for preserving cavernous nerves and erectile function after radical prostatectomy in the era of robotic surgery

A nerve-sparing procedure during robot-assisted radical prostatectomy has been considered one of the most important techniques for preserving postoperative genitourinary function. The reason is that adequate nerve-sparing procedures could preserve both erectile function and lower urinary tract function after surgery. When a nerve-sparing procedure is carried out, the cavernous nerves themselves cannot be visualized, despite the magnified viewing field during robot-assisted radical prostatectomy. Thus, nerve-sparing procedures have been considered challenging operations, even now. However, because not all surgeons have carried out a sufficient number of nerve-sparing procedures, the development of new nerve-sparing procedures or new methods for mapping the cavernous nerves is required. Recently, various new operative techniques, for example, Retzius-sparing robot-assisted radical prostatectomy, transvesical robot-assisted radical prostatectomy and retrograde release of neurovascular bundle technique during robot-assisted radical prostatectomy, have been developed. In addition, new surgical devices, for example, biological/bioengineering solutions for cavernous nerve protection and devices for identifying the cavernous nerves during radical prostatectomy, have developed to preserve the cavernous nerves. In contrast, limitations or problems in preserving cavernous nerves and postoperative erectile function have become apparent. In particular, the recovery rate of erectile function, the positive surgical margin rate at the site of nerve-sparing and the indications for nerve sparing have become obvious with the accumulation of much evidence. Furthermore, predictive factors for postoperative erectile function after nerve-sparing procedures have also been clarified. In this article, the importance of a comprehensive approach for early recovery of erectile function in the robot-assisted radical prostatectomy era is discussed.

Establishment of Novel Intraoperative Monitoring and Mapping Method for the Cavernous Nerve During Robot-assisted Radical Prostatectomy: Results of the Phase I/II, First-in-human, Feasibility Study

BACKGROUND

Potency preservation often does not meet expectation despite nerve-sparing prostatectomy.

OBJECTIVE

To set the protocol for intraoperative cavernous nerve monitoring and mapping during robot-assisted radical prostatectomy (RARP), and to evaluate its safety and clinical feasibility.

DESIGN, SETTING, AND PARTICIPANTS

A prospective phase I/II, feasibility study was performed. A total of 30 patients with prostate cancer who underwent RARP at a high-volume tertiary academic hospital were enrolled.

SURGICAL PROCEDURE

Pudendal somatosensory evoked potential, bulbocavernosus reflex, spontaneous corpus cavernosum electromyography (CC-EMG), median nerve stimulation evoked CC-EMG, and neurovascular bundle (NVB)-triggered CC-EMG with various stimulation protocols were assessed during conventional RARP under total intravenous anesthesia with controlled muscle relaxation.

MEASUREMENTS

The primary endpoint was the completion rate of planned surgery and assessment. Adverse events, and erectile and urinary functions were evaluated within 1 yr. CC-EMGs were graded and correlated with functional outcomes.

RESULTS AND LIMITATIONS

The completion rate was 100%. Only one patient experienced adverse events, which were not related to study intervention. Grades of CC-EMGs including NVB-triggered CC-EMG before prostate removal were associated with baseline five-item International Index of Erectile Function (IIEF-5) score (grades 0-1, 4.6±2.7; grade 2, 13.2±6.8; grades 3-4, 16.6±5.9; p=0.003). Furthermore, grades of CC-EMGs including NVB-triggered CC-EMG after prostate removal were significantly associated with potency recovery (grade 0, 12.5%; grade 1, 0%; grade 2, 33.3%; grades 3-4, 100% at 12 mo; p=0.005) and postoperative IIEF-5 scores at all evaluation time points (grades 0-1, 2.6±2.8; grade 2, 4.3±5.8; grades 3-4, 15.7±11.0 at 12 mo; p=0.003).

CONCLUSIONS

We successfully established the protocol for safe intraoperative cavernous nerve monitoring and mapping using CC-EMG during RARP. Its grades were well correlated with erectile function.

PATIENT SUMMARY

In this first-in-human feasibility study, we successfully established the protocol for safe intraoperative cavernous nerve monitoring and mapping method during robot-assisted radical prostatectomy. The results were significantly associated with erectile function. Evaluation of clinical efficacy to preserve potency seems worthy of further optimization and investigation in confirmatory clinical trials.

Novel methods for mapping the cavernous nerves during radical prostatectomy

The cavernous nerves, which course along the surface of the prostate gland, are responsible for erectile function. During radical prostatectomy, urologists are challenged in preserving these nerves and their function. Cavernous nerves are microscopic and show variable location in different patients; therefore, postoperative sexual potency rates are widely variable following radical prostatectomy. A variety of technologies, including electrical and optical nerve stimulation, dye-based optical fluorescence and microscopy, spectroscopy, ultrasound and magnetic resonance imaging have all been used to study cavernous nerve anatomy and physiology, and some of these methods are also potential intraoperative methods for identifying and preserving cavernous nerves. However, all of these technologies have inherent limitations, including slow or inconsistent nerve responses, poor image resolution, shallow image depth, slow image acquisition times and/or safety concerns. New and emerging technologies, as well as multimodal approaches combining existing methods, hold promise for improved postoperative sexual outcomes and patient quality of life following radical prostatectomy.

Preservation of the neurovascular bundles is associated with improved time to continence after radical prostatectomy but not long-term continence rates: results of a systematic review and meta-analysis

CONTEXT

The aetiology of urinary incontinence following radical prostatectomy (RP) is incompletely understood. In particular, it is unclear whether there is a relationship between neurovascular bundle (NVB) sparing and post-RP urinary continence.

OBJECTIVE

To review systematically the association of NVB sparing in RP with postoperative urinary continence outcomes and synthesise the results in a meta-analysis.

EVIDENCE ACQUISITION

This study was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-analysis statement. PubMed, Medline, and Cochrane Central Register of Controlled Trials were searched (December 2013), yielding 3413 unique records. A total of 27 longitudinal cohort studies were selected for inclusion. Studies were evaluated using a predefined criteria adapted from the Cochrane Tool to Assess Risk of Bias in Cohort Studies.

EVIDENCE SYNTHESIS

Data from 13 749 participants in 27 studies were synthesised in a meta-analysis. An assessment of the study methodology revealed a high risk of bias due to differences in baseline characteristics, outcome assessment, and the likely presence of unreported confounding factors such as meticulous apical dissection. Meta-analysis demonstrated that nerve sparing (NS) compared with non-nerve sparing (NNS) resulted in improved early urinary continence rates up to 6 mo postoperatively. Beyond this time, no significant difference was observed. This effect was seen most clearly for bilateral NS compared with NNS. A sensitivity analysis of prospective cohort studies revealed consistent results.

CONCLUSIONS

This analysis demonstrates an association between NS and improved urinary continence outcomes up to 6 mo postoperatively. NS in men with poor preoperative erectile function should be considered in the context of oncologic risk stratification because it may improve time to continence recovery. The underlying cause of the relationship between NS and continence is unknown. It may represent preservation of the intrapelvic somatic nerves supplying the rhabdosphincter or the influence of other confounding factors. Future research should be directed towards improving understanding of the anatomy of urinary continence and the pathophysiology of post-RP incontinence.

PATIENT SUMMARY

We found that avoiding damage to the nerves around the prostate improves urinary continence in the first 6 mo after surgery. After this time, there is no difference in continence between men who had these nerves removed and those who had them saved. This finding could be due to a true effect of saving these nerves or to a number of other factors affecting the research.

Interpositional Nerve Grafting of the Prostatic Plexus after Radical Prostatectomy

Background:

Injury to the prostatic plexus may occur during radical prostatectomy even with the use of minimally invasive techniques. Reconstruction of these nerves by interpositional nerve grafting can be performed to reduce morbidity. Although the feasibility of nerve reconstruction has been shown, long-term functional outcomes are mixed, and the role of nerve grafting in these patients remains unclear.

Methods:

A retrospective study was performed on 38 consecutive patients who underwent immediate unilateral or bilateral nerve reconstruction after open prostatectomy. Additionally, 53 control patients who underwent unilateral, bilateral, or non–nerve-sparing open prostatectomy without nerve grafting were reviewed. Outcomes included rates of urinary continence, erections sufficient for sexual intercourse, and ability to have spontaneous erections. Analysis was performed by stratifying patients by D’Amico score and laterality of nerve involvement.

Results:

Unilateral nerve grafting conferred no significant benefit compared with unilateral nerve-sparing prostatectomy. Bilateral nerve-sparing patients demonstrated superior functional outcomes compared with bilateral non–nerve-sparing patients, whereas bilateral nerve-grafting patients displayed a trend toward functional improvement. With increasing D’Amico score, there was a trend toward worsening urinary continence and erectile function regardless of nerve-grafting status.

Conclusions:

In the era of robotic prostatectomy, interpositional nerve reconstruction is not a routine practice. However, the substantial morbidity experienced in patients with bilateral nerve resections remains unacceptable, and therefore, nerve grafting may still improve functional outcomes in these patients. Further investigation is needed to improve the potential of bilateral nerve grafting after non–nerve-sparing prostatectomy.

Landmarks in erectile function recovery after radical prostatectomy

The description of the nerve-sparing technique of radical prostatectomy by Walsh was one of the major breakthroughs in the surgical treatment of prostate cancer in the 20(th) century. However, despite this advance and consequent technological refinements to nerve-sparing surgery, a large proportion of men still suffer from erectile dysfunction (ED) as a complication of prostatectomy. A plethora of therapeutic approaches have been proposed to optimize erectile function recovery in these patients. Several preclinical and translational studies have shown benefits of therapies including PDE5 inhibitor (PDE5I) treatment, immunomodulation, neurotrophic factor administration, and regenerative techniques, such as stem cell therapy, in animal models. However, most of these approaches have either failed to translate to clinical use or have yet to be studied in human subjects. Penile rehabilitation with PDE5Is is currently the most commonly used clinical strategy, in spite of the absence of solid clinical evidence to support its use.

Continuous-wave infrared subsurface optical stimulation of the rat prostate cavernous nerves using a 1490-nm diode laser

OBJECTIVE

To optimize the infrared laser wavelength and optical nerve stimulation (ONS) parameters for both deep and rapid subsurface cavernous nerve (CN) stimulation in a rat model, in vivo.

MATERIALS AND METHODS

A 150-mW, 1490-nm diode laser providing an optical penetration depth (OPD) of 518 μm in water was operated in continuous-wave mode during stimulation of the CNs in 8 rats for 15 seconds irradiation time through a custom-built, single-mode fiber optic probe capable of producing a collimated, 1-mm diameter laser beam. Successful ONS was judged by an intracavernous pressure response in the rat penis. Subsurface ONS at 1490 nm was also compared with previous studies using 1455 nm and 1550 nm near-infrared diode laser wavelengths.

RESULTS

Subsurface ONS of the rat CN was successful through fascia layers with a thickness up to 380 μm using an incident laser power of ∼50 mW. Intracavernous pressure response times as short as 4.6 ± 0.2 seconds were recorded using higher laser powers below the nerve damage threshold.

CONCLUSION

The 1490-nm diode laser represents a compact, low cost, high power, and high quality infrared light source for use in ONS. This wavelength provides deeper penetration than 1455-nm diode laser and more rapid and efficient nerve stimulation than 1550-nm diode laser.

Subsurface near-infrared laser stimulation of the periprostatic cavernous nerves

Successful identification and preservation of the cavernous nerves (CN), which are responsible for sexual function and vulnerable to damage during prostate cancer surgery, will require subsurface detection of the CN's beneath a thin fascia layer. This study explores the feasibility of optical nerve stimulation (ONS) in the rat with a fascia layer placed over the CN. Two near-infrared diode lasers with wavelengths of 1455 and 1550 nm were operated in continuous-wave mode for stimulation of the CN in 8 rats, in vivo. Successful ONS was confirmed by an intracavernous pressure (ICP) response in the rat penis at 1455 nm through fascia with a thickness up to 110 μm and at 1550 nm through fascia with a thickness up to 450 μm. Higher incident laser power was required to produce an ICP response as fascia thickness was increased. Also, weaker and slower ICP responses were observed as fascia thickness was increased. Subsurface ONS of the rat CN at a depth of 450 μm using a 1550 nm laser is feasible as an intermediate step towards developing ONS as an intra-operative diagnostic tool for identification and preservation of the cavernous nerves during prostate cancer surgery.

Intraoperative cavernous nerve stimulation and Laser-Doppler flowmetry during radical prostatectomy

INTRODUCTION

Erectile dysfunction is a common side effect following radical prostatectomy mainly due to damage of the pelvic autonomic nerve fibers (cavernous nerves). Intraoperative electrical stimulation of the cavernous nerves while measuring changes in penile girth has previously been shown to provide the surgeon with feedback of nerve integrity.

AIM

To test the feasibility of recording changes in glans penis blood flow by Laser Doppler flowmetry from cavernous nerve stimulation.

METHODS

Fifteen patients with localized prostate cancer undergoing radical prostatectomy had electrical stimulation of the proximal and distal parts of the neurovascular bundles after prostate removal. The stimulation consisted of 30-40 seconds biphasic constant current (10-30 mA) with 0.5 millisecond pulse duration.

MAIN OUTCOME MEASURES

Stimulus induced changes in penile blood flow was recorded from a Laser Doppler probe attached to the glans penis. Changes in penile girth were simultaneously recorded from a mercury-in rubber strain gauge. Erectile function was evaluated three months after surgery.

RESULTS

Ten patients had stimulus induced increase in Laser Doppler flow unilaterally (N=7) or bilaterally (N=3). Out of 10 patients, 6 reported some preserved erectile function postoperatively at 3 months follow-up (indicating 6 true and 4 false positives). Three patients had no Doppler response from stimulation and had no postoperative erectile function postoperatively (indicating three true negatives). Two patients were excluded from the study due to bad signal quality in the Laser Doppler signal. In the majority of patients, stimulation produced increase in penile girth sensed by the strain gauge.

CONCLUSION

This preliminary report provides evidence that Laser Doppler Flowmetry is able to detect increased penile blood flow from intraoperative electrical stimulation of the neurovascular bundles. However, further improvement in the recording technique is required. Laser Doppler Flowmetry may also be feasible to confirm autonomic nerve sparing in women undergoing pelvic surgery.

Advances in imaging the neurovascular bundle

PURPOSE OF REVIEW

Much of the progress in improving potency outcomes after radical prostatectomy has been achieved due to a better visualization of the neurovascular bundle responsible for erectile function. We review the current literature evaluating the existing imaging modalities to image the neurovascular bundle around the prostate pre, intra, and postoperatively, thereby enabling development of surgical techniques for better preservation of nerve function.

RECENT FINDINGS

Imaging modalities like multiphoton microscopy, optical coherence tomography, Coherent anti-Raman spectroscopy, exogenous fluoroscopy using prostate-specific membrane antigen, and so on have led to a better appreciation of the neurovascular bundle, thus encouraging novel techniques in nerve preservation during radical prostatectomy.

SUMMARY

In an age of heightened patient expectations and increasing life expectancy, better visualization of the neurovascular bundle around the prostate using novel imaging modalities may provide breakthroughs in improving potency outcomes after radical prostatectomy.

Imaging guidance in minimally invasive prostatectomy

Minimally invasive prostatectomy, such as laparoscopic and robot-assisted prostatectomy, has become more popular, with similar short-term outcomes as open radical retropubic prostatectomy series. The purpose of this article is to review different imaging modalities that have been developed with a goal of further improving the surgical outcomes in minimally invasive prostatectomy.

Continuous-wave laser stimulation of the rat prostate cavernous nerves using a compact and inexpensive all single mode optical fiber system

BACKGROUND AND PURPOSE

Laser stimulation of the rat cavernous nerve (CN) recently has been demonstrated as an alternative to electrical stimulation for potential application in nerve mapping during nerve-sparing radical prostatectomy. Advantages include noncontact stimulation and improved spatial selectivity. Previous studies, however, have used large and/or expensive laser sources for stimulation. This study demonstrates the feasibility of optical stimulation of the rat CN, in vivo, using a compact, inexpensive all-single-mode fiberoptic system.

MATERIALS AND METHODS

A 1455-nm wavelength infrared diode laser beam was coupled into a 9-μm-core single-mode fiber for delivery through a 10F laparoscopic probe and used for laser stimulation of the CN in a total of eight rats, in vivo.

RESULTS

Laser stimulation of the CN was observed at threshold temperatures of 41°C, with intracavernous pressure response times as short as 4 s, and magnitudes up to 50 mm Hg, compared with baselines of 10 mm Hg.

CONCLUSION

This novel, all-single-mode-fiber laser nerve stimulation system introduces several advantages including: (1) lower cost laser; (2) more robust fiberoptic design, eliminating alignment and cleaning of bulk optical components; and (3) improved Gaussian spatial beam profile for simplified alignment of the laser beam with the nerve. With further development, laser nerve stimulation may be useful for identification and preservation of the CN during prostate cancer surgery.

Continuous-wave infrared optical nerve stimulation for potential diagnostic applications

Optical nerve stimulation using infrared laser radiation has recently been developed as a potential alternative to electrical nerve stimulation. However, recent studies have focused primarily on pulsed delivery of the laser radiation and at relatively low pulse rates. The objective of this study is to demonstrate faster optical stimulation of the prostate cavernous nerves using continuous-wave (cw) infrared laser radiation for potential diagnostic applications. A thulium fiber laser (λ=1870 nm) is used for noncontact optical stimulation of the rat prostate cavernous nerves in vivo. Optical nerve stimulation, as measured by an intracavernous pressure (ICP) response in the penis, is achieved with the laser operating in either cw mode, or with a 5-ms pulse duration at 10, 20, 30, 40, 50, and 100 Hz. Successful optical stimulation is observed to be primarily dependent on a threshold nerve temperature (42 to 45 °C), rather than an incident fluence, as previously reported. cw optical nerve stimulation provides a significantly faster ICP response time using a lower power (and also less expensive) laser than pulsed stimulation. cw optical nerve stimulation may therefore represent an alternative mode of stimulation for intraoperative diagnostic applications where a rapid response is critical, such as identification of the cavernous nerves during prostate cancer surgery.

Interposition nerve grafting during radical prostatectomy: cumulative review and critical appraisal of literature

In 1997, the first report of sural nerve interposition grafting during radical prostatectomy was published in Urology. The favorable findings in this initial pilot study generated numerous follow-up reports that have demonstrated conflicting and contradictory outcomes. Certainly, controversy exists regarding the true benefit of nerve grafting. This review will objectively and critically summarize the salient literature, discuss evolving techniques, and offer insight into the future of interposition grafting in the current era of clinically localized prostate cancer and robotic prostatectomy.

Randomized phase II trial evaluation of erectile function after attempted unilateral cavernous nerve-sparing retropubic radical prostatectomy with versus without unilateral sural nerve grafting for clinically localized prostate cancer

BACKGROUND

Nonrandomized studies of unilateral nerve-sparing (UNS) radical prostatectomy (RP) have reported improved recovery of erectile function if the sacrificed cavernous nerve is reconstructed with a sural nerve graft (SNG).

OBJECTIVE

To determine whether UNS RP plus SNG results in a 50% relative increase in potency at 2 yr compared to UNS RP alone.

DESIGN, SETTING, AND PARTICIPANTS

The study enrolled patients from October 2001-May 2006 from a single academic center and was randomized, open label. Participants were men with localized prostate cancer recommended for UNS RP, less than 66 yr old, normal baseline erectile function, and willing to participate in early erectile dysfunction (ED) therapy. Patients were followed up to 2 yr.

INTERVENTION

Patients underwent UNS RP and ED therapy starting at 6 wk: oral prostaglandin type-5 (PDE5) inhibitor, vacuum erection device (VED), and intracavernosal injection therapy. In the SNG group, a plastic surgeon performed the procedure at the time of RP.

MEASUREMENTS

The ability to have an erection suitable for intercourse with or without a PDE5 inhibitor at 2 yr. The hypothesis was that SNG would result in a 60% potency rate compared to 40% for controls (80% power, 5% two-way significance).

RESULTS AND LIMITATIONS

The trial planned to enroll 200 patients, but an interim analysis at 107 patients met criteria for futility and the trial was closed. For patients completing the protocol to 2 yr, potency was recovered in 32 of 45 (71%) of SNG and 14 of 21 (67%) of controls (p=0.777). By intent-to-treat analysis, potency recovered in 32 of 66 (48.5%) of SNG and 14 of 41 (34%) of controls (p=0.271). No differences were seen in time to potency or quality of life scores for ED and urinary function. Limitations included slower-than-expected accrual and poor compliance with ED therapy: <65% for VED and <40% for injections.

CONCLUSIONS

The addition of SNG to a UNS RP did not improve potency at 2 yr following surgery.

TRIAL REGISTRATION

ClinicalTrials.gov, Identifier: NCT00080808, http://www.clinicaltrials.gov/ct2/show/NCT00080808?term=NCT00080808&rank=1.

Laser stimulation of the cavernous nerves in the rat prostate, in vivo: optimization of wavelength, pulse energy, and pulse repetition rate

The cavernous nerves on the prostate surface are responsible for erectile function. Improved diagnostic techniques are necessary for identification of the nerves during prostate cancer surgery and preservation of sexual function after surgery. Electrical mapping of the nerves has been used as an intra-operative tool during prostate surgery, but it has proven inconsistent and unreliable. Non-contact optical stimulation of the cavernous nerves in the rat prostate has recently been demonstrated as a potential alternative to electrical nerve stimulation. The purpose of this study is to optimize the laser parameters to provide the maximum intracavernosal pressure response after optical nerve stimulation in the rat prostate. Optimal laser nerve stimulation parameters provided comparable response to electrical nerve stimulation. Optical nerve stimulation may represent a potential intra-operative diagnostic technique for use in laparoscopic and robotic nerve-sparing prostate cancer surgery.

Intraoperative assessment of an implantable electrode array for cavernous nerve stimulation

INTRODUCTION

Erectile dysfunction remains a major functional complication of radical prostatectomy in the modern era despite surgical techniques to preserve the penile autonomic nerve supply.

AIM

To develop and evaluate a neurostimulation system for cavernous nerve electrical stimulation for future use as a chronic implantation device that neurotrophically promotes erectile function recovery following radical prostatectomy.

METHOD

After radical retropubic prostatectomy, the neurovascular bundle was stimulated using a temporarily placed electrode array of an implantable neurostimulation system (20 Hz frequency, 260 micro seconds pulse width, 5 mA-60 mA amplitude up to 10 minutes), and penile circumference increases were measured.

MAIN OUTCOME MEASURE

Increase in penile circumference. Results. Among 12 men (mean age 60.3 years) enrolled in this study, 6 (50%) demonstrated measurable increases in penile circumference in response to cavernous nerve stimulation. Among these six men, the mean increase was 5.0 mm (range 1.6 mm to 7.0 mm). Temporary surgical placement of the device was done with relative ease, and there was no evidence of injury to the neurovascular bundle. Conclusions. A chronic implantable nerve stimulation system for cavernous nerve stimulation having possible neuromodulatory effects on the recovery of penile erections after radical prostatectomy is feasible.

Fiberoptic imaging of cavernous nerves in vivo

PURPOSE

A critical intraoperative variable for the return of tumescence following radical prostatectomy is preservation of the cavernous nerves. We developed a nontoxic technique that would allow high resolution, in vivo real-time imaging specifically of the cavernous nerves.

MATERIALS AND METHODS

The cavernous nerves were labeled by injecting a fluorescent retrograde nerve tracer into the corpus cavernosum of male rats. Nerves were subsequently imaged in vivo using fiberoptic confocal fluorescent microscopy. Initial screening trials were performed to decide on a nerve tracer capable of axonal labeling, optimize injection concentration and characterize retrograde transport time. Toxicity studies included intracavernous pressure monitoring following electrical nerve stimulation, apoptotic staining of injected cavernous tissue and measurement of lipid peroxidation in nerves exposed to laser emissions during imaging.

RESULTS

In vivo real-time video sequences of fluorescently labeled cavernous nerves were recorded. The screening trial indicated that the B subunit of cholera toxin conjugated to AlexaFluor 488 (Invitrogen) provided optimal imaging after 9 days of retrograde transport. Toxicity studies showed that maximal intracavernous pressure responses did not differ between labeled and unlabeled nerves (p = 0.9671). Tracer injection did not increase apoptosis in cavernous tissue and laser exposure did not increase lipid peroxidation in nerves.

CONCLUSIONS

In vivo real-time imaging of the cavernous nerves is possible with no measurable toxicity, allowing the maintenance of erection. This novel imaging modality may allow urologists to identify cavernous nerves during pelvic surgery.

Intraoperative electrostimulation objectifies the assessment of functional nerve preservation after mesorectal excision

BACKGROUND

To improve nerve-sparing surgery, intraoperative electrical stimulation of pelvic autonomic nerves (INS) has been proposed in urology, gynecology, and visceral surgery. The aim of this study was to assess the impact of INS while monitoring intravesical pressure on the accurate evaluation of pelvic autonomic nerve preservation (PANP) after mesorectal excision. It was sought to determine whether this confirmation is useful in the prediction of postoperative urinary function.

METHODS

Sixty-two patients with mesorectal exzision for rectal cancer were examined prospectively. PANP was assessed visually by the surgeon and with INS. Bladder function was evaluated by post voiding residual volume measurement, rate of recatheterization, rate of long-term urinary catheterisation, and the international prostatic symptom score with quality of life index.

RESULTS

INS confirmed bilateral preservation of parasympathetic nerves in 46 patients (74%), and in 10 patients (16%) in at least one side. In six patients (10%), INS failed to confirm PANP. Eleven patients (18%) developed urinary symptoms postoperatively. INS results had a higher sensitivity than visual assessment by the surgeon (82 vs 46%). Values for specificity ranged at 90 and 92%, respectively. Accuracy of INS in predicting PANP was higher (88 vs 83%). The correlation between urinary function and the findings on INS was good (kappa-value: 0.65), correlation between urinary function and visual assessment by the surgeon was fair (kappa-value: 0.40).

CONCLUSION

INS, while monitoring intravesical pressure, accurately predicts bladder function after mesorectal excision. It may provide further insight into pelvic autonomic nerve sparing techniques.

Pelvic Autonomic Nerve Mapping Around the Prostate by Intraoperative Electrical Stimulation With Simultaneous Measurement of Intracavernous and Intraurethral Pressure

PURPOSE

In previous studies we noted that the neurovascular bundle was not identical to the bundle of the cavernous nerve fibers. In this study we sought to prove these anatomical findings electrophysiologically and map the autonomic nerve fibers by intraoperative simultaneous measurement of intracavernous pressure and intraurethral pressure.

MATERIALS AND METHODS

Between January 2004 and May 2005 electrical stimulation was performed in 27 open pelvic surgeries, including 26 radical retropubic prostatectomies and 1 radical cystectomy, using an original bipolar electrode before prostate removal. Nerve stimulation was performed at the base of the so-called neurovascular bundle (point A) and the rectal wall about 1 cm posterolateral, apart from the neurovascular bundle (point B). Intracavernous pressure and intraurethral pressure were measured simultaneously.

RESULTS

The mean +/- SD increase in intracavernous pressure was 9.8 +/- 6.3 cm H2O at point A and 13.5 +/- 7.3 cm H2O at point B. Intracavernous pressure at point B was significantly higher than at point A (p = 0.0240). The mean increase in intraurethral pressure was 17.0 +/- 9.4 cm H2O at point A and 11.2 +/- 8.1 cm H2O at point B. Intraurethral pressure at point A was significantly higher than at point B (p = 0.0353).

CONCLUSIONS

The course of the cavernous nerves did not always agree with the surgically identified neurovascular bundle. The distribution of cavernous nerves was wider than our image of the neurovascular bundle and it existed on the rectal wall posterolateral, apart from the neurovascular bundle rather than the neurovascular bundle itself. The surgically identified neurovascular bundle contained the nerve fibers contributing to urinary continence.

Reconstruction of cavernous nerves by nerve grafts to restore potency: contemporary review of technical principles and basic anatomy

PURPOSE OF REVIEW

The review discusses the efficacy of reconstructing the neurovascular bundle to regain sexual function if nerve-sparing prostatectomy is unfeasible.

RECENT FINDINGS

Eleven studies could be found describing the reconstruction of neurovascular bundles. All reconstructive procedures displayed technical inadequacies. The effectiveness of unilateral neurovascular bundle reconstruction remains statistically insignificant when compared with procedures without reconstruction. The efficacy of reconstructing both neurovascular bundles ranges between 0 and 43%. Concerning basic anatomy, the neurovascular bundle contains fibers innervating the cavernous nerves, prostate, rectum, and levator ani muscle. The terms cavernous nerve and neurovascular bundle have often been wrongly considered synonymous. The pelvic splanchnic nerves probably do not join the neurovascular bundle proximal to the bladder/prostate junction but rather at variable distances from 10 to 20 mm distal to it. Therefore, described proximal coaptation sites at the bladder/prostate junction possibly encompass only the hypogastric nerve.

SUMMARY

Modest clinical results are partly due to inadequate surgical techniques and are mainly due to the anatomical and topographical complexity of the cavernous nerves. Contemporary nerve grafting techniques probably do not allow for the regeneration of all cavernous nerves.

Significance of electrostimulation in detecting neurovascular bundle during radical prostatectomy

OBJECTIVE

The reported rate of erectile dysfunction after nerve-sparing prostatectomy varies according to physicians. Because exact preservation of the neurovascular bundle (NVB) solely depends on the judgment of the physician, he or she should try to correctly identify the NVB and also avoid neurophysiologic injury of the NVB during the procedure. The purpose of the present study is to assess the status of the NVB preservation by physician's judgment at the operation, the changes in intracavernous pressure related to intraoperative electrical stimulation and postoperative histopathological examination.

PATIENTS AND METHODS

Thirty-eight patients who underwent nerve-sparing radical prostatectomy judged by intraoperative electrical stimulation of the NVB were included in this study. Bilateral, unilateral and non-nerve-sparing procedures were performed in 18, 17, and 3 cases, respectively. The NVB preservation evaluated by intraoperative physician's judgment was compared to that evaluated by postoperative histopathological examination. Furthermore, the NVB preservation evaluated by intraoperative electrical stimulation was compared to that by physician's judgment and postoperative histopathological examination.

RESULTS

For 68 of 76 NVB (89.5%), intraoperative subjective judgment and histopathological assessment were identical. For 66 of 76 NVB (86.8%), electrical stimulation findings and the physician's judgments were identical, and for 70 of 76 NVB (92.1%), electrical stimulation findings and histopathological findings were identical.

CONCLUSION

Even if physicians are convinced of a successful nerve-sparing procedure, there are some cases in which the NVB is not preserved accurately or neurophysiological damage is suffered. Therefore, intraoperative electrical stimulation of the NVB as well as the cavernosal nerve is very useful in evaluation of NVB preservation.

Hope springs eternal: cavernosal nerve regeneration

Erectile dysfunction after radical prostatectomy for prostate cancer remains a significant morbidity for a large group of patients. A large body of work suggests that disrupting the cavernosal nerves is central as a causative factor. Extensive research has focused on ways to increase potency rates after surgery, either by preserving neuro-integrity, or attempting to restore it using various approaches. Herein we discuss the neurophysiology of nerve injury and regeneration, and review the work to date on cavernosal nerve regeneration.

Recent neuroanatomical studies on the neurovascular bundle of the prostate and cavernosal nerves: clinical reflections on radical prostatectomy

The neurovascular bundle of the prostate and cavernosal nerves have been used to describe the same structure ever since the publication of the first studies on the neuroanatomy of the lower urogenital tract of men, studies that were prompted by postoperative complications arising from radical prostatectomy. In urological surgery every effort is made to preserve or restore the neurovascular bundle of the prostate to avoid erectile dysfunction (ED). However, the postoperative potency rates are yet to be satisfactory despite all advancements in radical prostatectomy technique. As the technology associated with urological surgery develops and topographical studies on neuroanatomy are cultivated, new observations seriously challenge the classical teachings on the topography of the neurovascular bundle of the prostate and the cavernosal nerves. The present review revisits the classical and most recent data on the topographical anatomy of the neurovascular bundle of the prostate and cavernosal nerves and their implications on radical prostatectomy techniques.

Erectile dysfunction and treatment of carcinoma of the prostate

Prostate cancer is the leading malignancy in men in the United States and causes more than 60,000 deaths annually. Treatment of prostate cancer, whether it be with surgery, radiation therapy, cryotherapy, or medical treatment, is associated with significant life-altering morbidity. Incontinence and erectile dysfunction (ED) too often are sequelae of these treatment alternatives. ED can be a significant complication and can alter the life of the patient with prostate cancer and his partner. Newer modifications of the radical prostatectomy with nerve-sparing techniques are the cornerstone of erection preservation. Time following radical prostatectomy has been shown to increase erectile function such that more patients have functional erections at 3 years than 1 year after surgery. With the advent of phosphodiesterase-5 (PDE-5) inhibitors, many men can have improved functional erections and return to active coitus. Prevention of ED also is an important management technique. Evidence is gathering that prophylaxis with regular vasoactive injection or daily PDE-5 agents may be an integral part of preservation of corpus cavernosum smooth muscle function. Combination medical therapy and surgical penile prosthesis implantation also are options for patients who do not respond to oral PDE-5 inhibitors.

Functional anatomy of the prostate: implications for treatment planning

PURPOSE

To summarize the functional anatomy relevant to prostate cancer treatment planning.

METHODS AND MATERIALS

Coronal, axial, and sagittal T2 magnetic resonance imaging (MRI) and MRI angiography were fused by mutual information and registered with computed tomography (CT) scan data sets to improve definition of zonal anatomy of the prostate and critical adjacent structures.

RESULTS

The three major prostate zones (inner, outer, and anterior fibromuscular) are visible by T2 MRI imaging. The bladder, bladder neck, and internal (preprostatic) sphincter are a continuous muscular structure and clear definition of the preprostatic sphincter is difficult by MRI. Transition zone hypertrophy may efface the bladder neck and internal sphincter. The external "lower" sphincter is clearly visible by T2 MRI with wide variations in length. The critical erectile structures are the internal pudendal artery (defined by MRI angiogram or T2 MRI), corpus cavernosum, and neurovascular bundle. The neurovascular bundle is visible along the posterior lateral surface of the prostate on CT and MRI, but its terminal branches (cavernosal nerves) are not visible and must be defined by their relationship to the urethra within the genitourinary diaphragm. Visualization of the ejaculatory ducts within the prostate is possible on sagittal MRI. The anatomy of the prostate-rectum interface is clarified by MRI, as is the potentially important distinction of rectal muscle and rectal mucosa.

CONCLUSION

Improved understanding of functional anatomy and imaging of the prostate and critical adjacent structures will improve prostate radiation therapy by improvement of dose and toxicity correlation, limitation of dose to critical structures, and potential improvement in post therapy quality of life.

Recent trends in surgical treatment of localized prostate cancer

Prostate cancer and its various forms of treatment remain a source of significant controversy and morbidity despite recent advances. In response, there is an increasing trend toward the development of treatments aimed at cancer prevention and at maximizing the preservation of function without sacrificing cancer control. This article reviews the current prostate cancer literature and reports on improvements in existing surgical treatments and developing technologies aimed toward achieving these goals. Specific therapies addressed include improvements in surgical techniques, laparoscopy, robotics, cryosurgical and thermal ablation, and high-intensity focused ultrasound.

INTRAOPERATIVE ELECTROPHYSIOLOGICAL CONFIRMATION OF URINARY CONTINENCE AFTER RADICAL PROSTATECTOMY

PURPOSE

To determine the actual effect of nerve sparing radical retropubic prostatectomy (RP) on postoperative urinary continence we used intraoperative electrophysiological testing to confirm functional preservation of the neurovascular bundle (NVB).

MATERIALS AND METHODS

A total of 85 patients undergoing RP for localized prostate cancer were studied. During RP NVB preservation was assessed macroanatomically. Electrophysiological testing was then performed to confirm NVB preservation. The NVB was electrostimulated and responses were observed by monitoring intracavernous or intraurethral pressure changes. All patients were classified into 3 groups according to the degree of nerve sparing, that is a bilateral nerve sparing group, a unilateral nerve sparing group and a nonnerve sparing group, based on macroanatomical assessment as well as on electrophysiological assessment. Postoperative continence in each group was then determined. Urinary continence at baseline, and 3 and 6 months postoperatively was studied using a self-administered questionnaire.

RESULTS

With electrophysiological assessment 20.6% of macroanatomically determined NVB preservations were reclassified. Analysis of the data on groups classified accurately by electrophysiological testing showed that the bilateral nerve sparing group maintained postoperative urinary function significantly more than the unilateral nerve sparing and nonnerve sparing groups. However, when only macroanatomical assessment was considered, no significant difference among the groups was found in urinary function.

CONCLUSIONS

Electrophysiological assessment revealed that bilateral NVB preservation contributes to early recovery of urinary continence after RP. Thus, intraoperative electrophysiological assessment is useful for predicting postoperative quality of life.

Surgical management of prostate cancer: Advances based on a rational approach to the data

The management of localised prostate cancer has undergone important changes in the past two decades, with major improvements in surgical technique, a greater emphasis on structured assessment of quality of life, and a greater attempt to tailor treatment to biological risk. Disease diagnosis is predicated on identification of demographic risk factors, serum levels of prostate-specific antigen and its derivatives, and extended biopsy techniques. Surgical removal of the prostate may be accomplished by open or minimally invasive techniques and in experienced hands results in good functional outcomes a high rate of cure for those with organ confined disease. Radical prostatectomy is also appropriate in selected patients with locally advanced disease and after failed radiation therapy.

Neuroprotective strategies in radical prostatectomy

In this section, authors from New York give their views on the various neuroprotective strategies for patients having a radical prostatectomy, such as the use of nerve grafts and other approaches. A joint study from Korea, the USA, Canada and the UK is presented in a paper on the importance of patient perception in the clinical assessment and management of BPH. There is also a review of robotic urological surgery. Finally, authors from New York give a review on the life of Isaac Newton. This is a new historical review in the journal, but one that will be of general interest.

Cavernosal nerve mapping: current data and applications

Although nerve-sparing prostatectomy is widely practised, the results with respect to preserving potency often do not meet expectations. The concept of intraoperative cavernosal nerve stimulation is reasonable. Data that link the response to sildenafil after prostatectomy with bilateral nerve sparing has increased the importance of optimizing nerve sparing. The cavernosal nerves are often difficult to visualize and may have a variable course. A tumescent response to nerve stimulation can be shown consistently; the response may be subtle, and characterized by a minimal increase in penile circumference and blood flow. Immediately after prostatectomy, proximal nerve stimulation identifies whether neural continuity has been maintained, and is predictive of recovery of erectile function. The Cavermap system (Uromed Corporation, Boston, MA, USA) was developed to permit intraoperative nerve stimulation with tumescence monitoring. An initial phase 2 and subsequent phase 3 single-blinded, randomized, multicentre study that compared Cavermap-assisted prostatectomy with conventional nerve sparing showed a significant benefit in terms of the duration of nocturnal tumescence at 1 year. Other approaches are being explored, including incorporating the device into sural or genito-femoral nerve grafting, use of nerve stimulation during cystectomy or abdominal-perineal resection, and direct corpus cavernosal pressure monitoring during nerve stimulation. These approaches warrant further evaluation.

Potency after unilateral nerve sparing surgery: a report on functional and oncological results of unilateral nerve sparing surgery

The objective of the study was to evaluate unilateral nerve sparing prostate surgery. Patient files of men who underwent unilateral nerve sparing radical prostatectomy were analyzed retrospectively after a minimum follow-up period of 18 months. Of 46 patients who received unilateral nerve sparing surgery, 14 (30.4%) regained full potency after surgery. In 92.9% of these patients, recovery occurred within a period of 18 months. Age is the single most important factor in the recuperation of potency after unilateral nerve sparing surgery. Most of the patients (84.8%) reported the ability to achieve orgasm. Of eight patients with positive section margins, two had positive section margins at the spared side only. Unilateral nerve sparing surgery remains a feasible treatment option for prostate cancer.

Therapies for neurologic erectile dysfunction

A subset of men with erectile dysfunction have an underlying neurologic or neurodegenerative condition which directly causes their impairment. The authors briefly discuss the interplay of the CNS, peripheral nervous system and corporal bodies of the penis integral to normal erectile function and how these interactions are disrupted in the setting of various neurologic conditions. Effective therapies for these patients exist in a variety of different forms to include oral or injectable drugs and even surgery. Future treatment strategies will focus on the improvement of existing therapies as well as the invention of new long-term therapeutic options.

Intraoperative electrical stimulation of cavernous nerves with monitoring of intracorporeal pressure to confirm nerve sparing during radical prostatectomy: Early clinical results

BACKGROUND

We performed intraoperative cavernous nerve stimulation with an intracavernous pressure (ICP) monitoring system to confirm nerve sparing during radical pelvic surgery and assessed the results.

METHODS

Nineteen cases of radical prostatectomy and three of radical cystoprostatectomy were examined. Electrical stimulation of the site where the neurovascular bundle (NVB) was determined to run was performed and changes in ICP were measured before and after prostate removal.

RESULTS

Of the 22 patients, bilateral NVBs were preserved in six patients while unilateral NVB was preserved in 16. Before dissection, all NVBs examined exhibited positive responses (ICP changes of>5 mmHg) to nerve stimulation. After removal of the prostate, positive responses were observed in 22 (79%) of 28 macroanatomically preserved NVBs. Of 16 sides on which the NVB was not preserved, there were positive responses in five (31%). In these patients, some nerve fibers were macroscopically observed lateral to the original site of NVB. Finally, bilateral or unilateral nerve sparing was confirmed electrophysiologically in 20 (91%) of the 22 patients.

CONCLUSION

Intraoperative stimulation of the NVB while monitoring ICP changes is a simple and reliable method of accurately evaluating the preservation of cavernous nerves. This system may provide further insight into the mechanism of postoperative erectile dysfunction.

Preliminary results of a monitoring system to confirm the preservation of cavernous nerves

BACKGROUND

It is important to preserve the neurovascular bundle (NVB) during nerve-sparing surgery. This article presents the preliminary results of our monitoring system for the postoperative preservation of erectile function.

METHODS

In 15 patients undergoing radical prostatectomy and 20 patients undergoing radical cystoprostatectomy, intraoperative electrical stimulation along the NVB was performed to measure changes in intracavernous pressure before and after prostate removal. Seven of the radical prostatectomy patients and eight of the radical cystoprostatectomy patients underwent nerve-sparing surgery. Postoperative erectile function was evaluated in 25 patients not receiving adjuvant hormonal therapy.

RESULTS

The NVB was judged to be preserved at least on one side electrophysiologically in 14 of 15 patients. Pathologically, three patients had pT3 cancer. Postoperatively, sufficient erectile function was demonstrated using the International Index of Erectile Function 5 in three patients, nocturnal penile tumescence in three patients, and a questionnaire or an interview in three patients. The other patients were incompletely erectile. None of the 11 patients not receiving adjuvant hormonal therapy, in whom NVB was not preserved, were erectile.

CONCLUSION

If the successful criterion of nerve-sparing surgery is defined as a change in intracavernous pressure of 4 cm H2O or more being observed at least unilaterally, and the successful criteria of erectile function preservation includes being sufficiently erectile as revealed by an interview, the sensitivity of our system was 69.2% (9/13) and the specificity was 100% (12/12). Neither adverse reactions to the measurement, nor inadequacy of cancer excision accompanying NVB sparing, were observed. These results suggest that our system can predict postoperative erectile function fairly accurately.

Erectile function after radical prostatectomy: a review

OBJECTIVES

Although the high rate of erectile dysfunction (ED) following prostatectomy is well recognised, the aetiology and pathophysiology have not yet been fully elucidated. We examined the current literature as to aetiology, treatment and possible prevention of ED following prostatectomy.

METHOD

Review of the literature by a Medline search.

CONCLUSION

The most important predictors of erectile function are pre-operative erectile function and the nerve sparing nature of the procedure. The former is determined by age and vascular risk-factors whereas the latter is decided by the stage of the tumour and the skill of the surgeon. The value of intraoperative nerve mapping seems limited and the importance of nerve grafting is uncertain. Natural recovery of erection can take as long as 24 months. Patients complain about a lack of professional support. Symptomatic therapy may be applied according to the current general standards of treatment in men with ED.

Intraoperative parasympathetic nerve stimulation with tumescence monitoring during total mesorectal excision for rectal cancer

BACKGROUND

Unilateral or bilateral division of the parasympathetic nerves during resection of rectal cancer may result in sexual erectile dysfunction. The purposes of this project were twofold: to determine the ability to demonstrate penile tumescence in response to parasympathetic nerve stimulation after rectal cancer resection and to correlate the nerve stimulation response with clinical sexual function 6 months after operation.

STUDY DESIGN

In 21 consecutive male patients with normal erectile function undergoing total mesorectal excision, cavernous nerve identification and integrity before and after pelvic dissection were assessed intraoperatively, both visually by an experienced surgeon and by using the CaverMap nerve stimulator. The minimal effective current necessary to produce a 2% increase in penile tumescence was recorded for both the left- and right-sided nerves, primarily the largest nerve trunk, S3. Postclearance stimulation data were then correlated with sexual function outcomes, specifically erection and orgasm at 6 months after surgery.

RESULTS

The operating surgeon's visual assessment of the pelvic autonomic nerve's integrity after pelvic dissection was deemed intact in 20 of the 21 patients (95.2%). Of the 20 patients who were evaluated with CaverMap after completion of total mesorectal excision, 17 (85%) had tumescence response after nerve stimulation on either side, and 3 patients (15%) had unilateral response only. Of the 19 patients evaluated for sexual function 6 months after surgery, 18 (94.7%) had normal function, including the 3 patients with only unilateral nerve stimulation tumescence response.

CONCLUSIONS

Intraoperative mapping of the parasympathetic nerve trunks with the CaverMap nerve stimulator may be a valuable aid to less experienced pelvic surgeons and may help in autonomic nerve preservation during total mesorectal excision clearance.