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

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.

European Society for Sexual Medicine Consensus Statement on the Use of the Cavernous Nerve Injury Rodent Model to Study Postradical Prostatectomy Erectile Dysfunction

INTRODUCTION

Rodent animal models are currently the most used in vivo model in translational studies looking into the pathophysiology of erectile dysfunction after nerve-sparing radical prostatectomy.

AIM

This European Society for Sexual Medicine (ESSM) statement aims to guide scientists toward utilization of the rodent model in an appropriate, timely, and proficient fashion.

METHODS

MEDLINE and EMBASE databases were searched for basic science studies, using a rodent animal model, looking into the consequence of pelvic nerve injury on erectile function.

MAIN OUTCOME MEASURES

The authors present a consensus on how to best perform experiments with this rodent model, the details of the technique, and highlight possible pitfalls.

RESULTS

Owing to the specific issue-basic science-Oxford 2011 Levels of Evidence criteria cannot be applied. However, ESSM statements on this topic will be provided in which we summarize the ESSM position on various aspects of the model such as the use of the Animal Research Reporting In Vivo Experiments guideline and the of common range parameter for nerve stimulation. We also highlighted the translational limits of the model.

CONCLUSION

The following statements were formulated as a suggestive guidance for scientists using the cavernous nerve injury model. With this, we hope to standardize and further improve the quality of research in this field. It must be noted that this model has its limitations. Weyne E, Ilg MM, Cakir OO, et al. European Society for Sexual Medicine Consensus Statement on the Use of the Cavernous Nerve Injury Rodent Model to Study Postradical Prostatectomy Erectile Dysfunction. Sex Med 2020;8:327-337.

Anatomical robotic prostatectomy: technical factors to achieve superb continence and erectile function

Debate continues as to the superiority of robotic versus open radical prostatectomy for the surgical treatment of localized prostate cancer. Despite this controversy, retrospective data from high volume centres has demonstrated RARP is associated with improved pentafecta outcomes with lower transfusion rates, less incontinence, lower positive surgical margins and improved potency. Advocates of robotic assisted radical prostatectomy (RARP) believe an enhanced visual field, the precision afforded by robotic technology as well as lack of bleeding, sharp dissection and delicate tissue handling lead to improved outcomes. Prostate Cancer is the second most common cancer diagnosed in men, and as the number of post-surgical patients increases, the complications of urinary incontinence and erectile dysfunction not only have a significant negative impact on patients' quality of life, but have become an expanding part of clinical practice. This article outlines what are believed to be the most important strategies based on anatomical knowledge and technical expertise, that allow robotic prostatectomists to achieve superb outcomes in urinary and erectile function.

Anatomic robotic prostatectomy: current best practice

Urologic prostate surgery has changed dramatically over the past decades. Following the introduction of the robot, the surgical approach has been modified and thanks to the magnification allowed by the robot a further level of precision can be achieved. Moreover, advances in the anatomical studies have provided new evidence regarding the periprostatic anatomy. The aim of this review is to describe our approach to robot-assisted radical prostatectomy. Our holistic perspective towards patient selection, pre- and postoperative care is provided. In our center, robot-assisted radical prostatectomy is performed by means of an anterograde approach. A nonbladder-sparing dissection with a graded approach towards nerve preservation is carried out. The procedure is concluded with what we call 'total anatomical reconstruction'.

Evoked cavernous activity: neuroanatomic implications

We investigated the autonomic innervation of the penis by using evoked cavernous activity (ECA). We recruited seven men with thoracic spinal cord injury (SCI) and sexual dysfunction, and six men who were scheduled to have pelvic surgery (PS), specifically non-nerve-sparing radical cystoprostatectomy. In the PS patients, ECA was performed both pre- and postoperatively. The left median nerve was electrically stimulated and ECA was recorded with two concentric electromyography needles placed into the right and left cavernous bodies. We simultaneously recorded hand and foot sympathetic skin responses (SSRs) as controls. In the SCI group, all but one patient had reproducible hand SSRs. None of these patients had ECA or foot SSRs. All the PS patients had reproducible ECA and SSRs, both preoperatively and postoperatively. There was no difference in the latency and amplitude measurements of ECA and SSRs in the postoperative compared with that of the pre-operative period (P>0.05). In conclusion, ECA is absent in men with SCI above the sympathetic outflow to the genitalia. In men, after radical pelvic surgery, ECA is preserved, indicating the preservation of sympathetic fibers.

KTP laser nerve sparing radical prostatectomy: comparison of ultrasonic and cold scissor dissection on cavernous nerve function

PURPOSE

Energy sources used during nerve sparing radical prostatectomy are known to compromise cavernous nerve function. Lasers offer the potential for accurate dissection while minimizing collateral injury to delicate neural structures. We evaluated cavernous nerve function following KTP laser dissection and compared outcomes to those of ultrasonic shears and cold scissor dissection.

MATERIALS AND METHODS

Laparoscopic unilateral neurovascular bundle mobilization was performed in 36 survival dogs using a KTP laser, ultrasonic shears and an athermal technique with cold scissors and clips in 12 each. Peak intracavernous pressure upon cavernous nerve stimulation, expressed as a percent of mean arterial pressure, was measured acutely and at 1 month. Thermal spread from the KTP laser and ultrasonic shears was assessed histologically ex vivo in harvested peritoneum.

RESULTS

Median peak intracavernous pressure as a percent of mean arterial pressure was similar immediately and 1 month after laser and athermal dissection, and significantly decreased after dissection with ultrasonic shears. Acute peak intracavernous pressure as a percent of mean arterial pressure was 53%, 96% and 98% for ultrasonic shears, laser and the athermal technique, respectively (laser vs athermal p = 0.51, ultrasonic shears vs laser p <0.001 and ultrasonic shears vs athermal p <0.001). Chronic peak intracavernous pressure as a percent of mean arterial pressure was 56%, 98% and 100% for ultrasonic shears, laser and the athermal technique, respectively (laser vs athermal p = 0.38, ultrasonic shears vs laser p = 0.016 and ultrasonic shears vs athermal p = 0.013). The median depth of acute laser injury was 600 microm compared to 1.2 mm for ultrasonic shear dissection and 450 microm crush injury due to the athermal technique. Thermography revealed less collateral thermal spread from the laser than from the ultrasonic shears (median greater than 60C thermal spread 1.07 vs 6.42 mm, p <0.01).

CONCLUSIONS

The KTP laser was comparable to the athermal technique and superior to the ultrasonic shears for preserving cavernous nerve function.

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.

Effects of transanal pelvic plexus stimulation on penile erection: clinical implications

OBJECTIVE

To determine the ability of transanal pelvic plexus stimulation (TPPS) in inducing penile tumescence in patients with non-neurogenic erectile dysfunction (ED) and to compare the erection degree with papaverine-induced erection.

PATIENTS AND METHODS

The cavernous electrical activity (CEA) in 21 men with non-neurogenic erectile dysfunction was measured during TPPS by electromyography of corpus cavernosum and the erection degree of penis (flaccid, semi-rigid, rigid) was noted. The stimulation amplitude was increased from 20 to 100 mA. All patients also underwent intracavernous papaverine injection and further CEA recordings were obtained.

RESULTS

Twelve and nine patients were diagnosed with vasculogenic (VED) and non-vasculogenic ED (NVED), respectively. TPSS led to a penile erectile response in 12 patients (57%), whereas papaverine injection caused erection in 16 (76.2%) patients. The mean baseline CEA (16.9 +/- 9.1 mV) did not change with TPPS, but papaverine significantly decreased the mean CEA to 12.3 +/- 4.9 mV (P < 0.001). CEA recordings of 16 (76.2%) patients revealed a significant decrease after papaverine injection, however seven (33.3%) patients showed significant CEA decrease in response to TPPS. Both TPPS and papaverine were observed to have a higher effect in patients with NVED in terms of inducing penile erection and decreasing CEA compared to their effects in patients with VED.

CONCLUSION

TPPS induces penile erection and decreases CEA for some extent, but to a lesser degree compared to papaverine. As further improvements are achieved in the methodology of TPPS, it may be a valuable method in the evaluation patients with erectile dysfunction.

Impact of unilateral interposition sural nerve graft on the recovery of sexual function after radical prostatectomy in Japanese men: a preliminary study

PURPOSE

To determine the effect of an interposition nerve graft on sexual function after radical prostatectomy.

METHODS

This study includes 64 patients, without hormonal therapy, who underwent a radical prostatectomy and intraoperative electrophysiological confirmation of cavernous nerve preservation. Twelve patients underwent a unilateral interposition sural nerve graft (UNG) for the resected neurovascular bundle. Twenty-one and 31 patients underwent bilateral nerve-sparing (BNS) and unilateral nerve-sparing (UNS) surgery without a nerve graft, respectively. As the age of patients was significantly younger in the UNG group than in the other groups, age-matched analysis also was conducted. Sexual function, evaluated by a self-administered questionnaire using the University of California Los Angeles-Prostate Cancer Index, was compared statistically among the three groups.

RESULTS

In the age-matched analysis, the postoperative sexual function (SXF) score of the UNG group showed an intermediate level of recovery between those of the BNS and UNS groups at 12 months and reached the same level as the score at 12 months of the BNS group at 18 months postoperatively. The difference in the SXF score between the UNG and UNS groups began to appear after 6 months postoperatively and increased steadily with time. However, the background factors, such as the baseline SXF score, the usage rate of phosphodiesterase 5 inhibitors, and the rate of comorbidities were different between the UNG and UNS groups.

CONCLUSIONS

The difference of the SXF score between the UNG and UNS groups increased with time after 6 months postoperatively. However, it might be difficult at present to attribute a better recovery of the SXF score to the nerve graft because of the difference in the background factors between the groups.

Relevance of postcatheter removal incontinence to postoperative urinary function after radical prostatectomy

AIM

We examined whether postoperative urinary function after radical prostatectomy is associated with immediate incontinence just after catheter removal.

PATIENTS AND METHODS

The current study included 80 patients with clinically localized prostate cancer, who underwent radical retropubic prostatectomy between January 2002 and May 2004. The amount of immediate incontinence was measured with a 24-h pad test just after catheter removal. The patients were categorized into the three groups based on the stratified grade of immediate urinary incontinence: groups I (0 g; 47 patients), II (1-99 g; 23 patients) and III (100 g and above; 10 patients), respectively. Urinary function and bother were assessed by a self-administered questionnaire using the University of California Los Angeles, Prostate Cancer Index at baseline, and at 3, 6 and 12 months postoperatively. The differences in scores of urinary function, bother and clinicopathological parameters were assessed in the three groups with one-way analysis of variance.

RESULTS

No significant difference was observed in the clinicopathological parameters in the three groups. Preoperatively significant difference of urinary function scores was not evident and that of urinary bother scores was not observed in the three groups. Postoperatively urinary function scores were significantly different throughout the postoperative periods investigated, whereas difference in urinary bother scores observed at 3 months tended to disappear with time.

CONCLUSION

Postcatheter removal incontinence might be related to postoperative urinary function after radical prostatectomy, although further investigation is necessary regarding the criteria for categorization because of a small number of the patients.

The proximal neurovascular plate and the tri-zonal neural architecture around the prostate gland: importance in the athermal robotic technique of nerve-sparing prostatectomy

OBJECTIVE

To review the neural architecture around the prostate gland, as it is relevant for nerve-sparing robotic prostatectomy, including in particular the anatomy of the proximal neurovascular tissue, the neurovascular bundle (NVB), and accessory neural pathways (ANPs).

MATERIALS AND METHODS

The aims of this study were achieved in collaboration between the Cornell Institute of Robotic Surgery, New York, NY, USA and the Institute of Urology at the University of Innsbruck, Austria. The broad steps were: (i) anatomical studies of 10 fresh and two fixed male cadavers; and (ii) collection of videotape and still image data from 200 men undergoing radical prostatectomy by the athermal robotic technique at the Cornell Institute.

RESULTS

From a surgical standpoint there was a tri-zonal neural architecture including the proximal neurovascular plate (PNP), the predominant NVB (PNB) and ANPs. The PNP was a mean (range) of 5 (3-10) mm lateral to the seminal vesicles, was 3 (2-7) mm thick, 7 (5-25) mm wide and 9 (4-30) mm long. It was within 6 (4-15) mm of the bladder neck, 5 (2-7) mm of the endopelvic fascia and overlapped 5 (0-7) mm of the proximal prostate. The PNB varied in shape and size from the proximal to distal end, was thickest at the base and most variable near the apex. In eight of 12 cases, there was a medial extension behind the prostate, which converged medially at the apex in four cases. ANPs were noted within the layers of levator fascia and/or lateral pelvic fascia on the anterolateral aspect in five cases and in three on the posterior aspect of the prostate. In nine cadavers, the proximal third of the prostate was covered by the PNP where these ANPs were most prominent. The ANPs formed a plexus on the posterolateral aspect of the apex in four cases.

CONCLUSION

We have created an anatomical map of neurovascular tissue relevant to robotic prostatectomy. A tri-zonal neural architecture is described which has helped in standardizing the steps of robotic prostatectomy.

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.

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.

Intraoperative Electrophysiological Confirmation of Neurovascular Bundle Preservation during Radical Prostatectomy: Long-term Assessment of Urinary and Sexual Function

OBJECTIVE

We investigated the longitudinal recovery of urinary and sexual function after radical retropubic prostatectomy (RP) using an intraoperative electrophysiological test to confirm the functional preservation of the neurovascular bundle (NVB).

METHODS

A total of 70 patients who underwent RP for localized prostate cancer were prospectively enrolled in our survey. During RP, electrophysiological testing was performed to confirm the NVB preservation. The NVB was electrostimulated and the responses were observed by monitoring the intracavernous or intraurethral pressure changes. All patients were classified into three groups according to the degree of nerve-sparing [a bilateral nerve-sparing group (BNS), a unilateral nerve-sparing group (UNS) and a non-nerve-sparing group (NNS)] based on the macroanatomical as well as the electrophysiological assessment. Both urinary and sexual function were measured before and 3, 6, 12 and 24 months after RP by a self-administered questionnaire.

RESULTS

The concordance rate of nerve-sparing or non-nerve-sparing between the electrophysiological and macroanatomical assessment was 80%. According to the electrophysiological data, the BNS maintained significantly better urinary function at 3 months after RP than the NNS and UNS. After 6 months, each group had almost recovered continence. When considering sexual function, the BNS showed better sexual function scores than the NNS throughout the post-operative periods and the UNS at 2 years. According to the macroanatomical assessment, however, these differences were significant.

CONCLUSIONS

Nerve-sparing RP as confirmed by intraoperative electrophysiological test may contribute significantly to the early recovery of continence and greater rate of sexual function after RP.

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.

Variation in course of cavernous nerve with special reference to details of topographic relationships near prostatic apex: Histologic study using male cadavers

OBJECTIVES

To study interindividual variation in the cavernous nerve course near the rhabdosphincter and the apex of the prostate as a basis for refining nerve-sparing radical prostatectomy. The varying anatomy of the cavernous nerve might account for the disparate potency rates after nerve-sparing radical prostatectomy.

METHODS

We examined serial histologic sections from 20 male pelves (7 frontal, 8 sagittal, and 5 axial sections) and performed 5 fresh cadaver dissections.

RESULTS

In the fresh dissections, the macroscopically identified neurovascular bundle consistently showed an almost straight proximal-to-distal course along the urethra. However, on histologic analysis, the types of the nerve course were classified as frontal (2 of 7 specimens), sagittal (3 of 8), and axial (2 of 5). In the frontal and sagittal courses, the nerves passed through the connective tissue of a narrow potential space between the rhabdosphincter and the levator ani. In the specimens showing an axial course, the nerves were spatially distinct from the prostate, coursing ventromedially in the pararectal space. Thus, the nerves could display a long, tortuous course, passing through the rectourethral muscle at its thickest portion. In addition, a nerve component supplying the area of the rhabdosphincter seemed to accompany the cavernous nerve.

CONCLUSIONS

The neurovascular bundle, previously defined in terms of surgery, is likely to differ from the actual course of the cavernous nerve when this is axial, passing through the pararectal space and rectourethral muscle. To avoid cavernous nerve injury, the rectourethral muscle must be managed carefully in both the retropubic and the perineal approaches.