Intraoperative electrical stimulation of cavernosal nerves with monitoring of intracorporeal pressure in patients undergoing nerve sparing radical prostatectomy

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.

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.

Improved Intraoperative Visualization of Nerves through a Myelin-Binding Fluorophore and Dual-Mode Laparoscopic Imaging

The ability to visualize and spare nerves during surgery is critical for avoiding chronic morbidity, pain, and loss of function. Visualization of such critical anatomic structures is even more challenging during minimal access procedures because the small incisions limit visibility. In this study, we focus on improving imaging of nerves through the use of a new small molecule fluorophore, GE3126, used in conjunction with our dual-mode (color and fluorescence) laparoscopic imaging instrument. GE3126 has higher aqueous solubility, improved pharmacokinetics, and reduced non-specific adipose tissue fluorescence compared to previous myelin-binding fluorophores. Dosing and kinetics were initially optimized in mice. A non-clinical modified Irwin study in rats, performed to assess the potential of GE3126 to induce nervous system injuries, showed the absence of major adverse reactions. Real-time intraoperative imaging was performed in a porcine model. Compared to white light imaging, nerve visibility was enhanced under fluorescence guidance, especially for small diameter nerves obscured by fascia, blood vessels, or adipose tissue. In the porcine model, nerve visualization was observed rapidly, within 5 to 10 minutes post-intravenous injection and the nerve fluorescence signal was maintained for up to 80 minutes. The use of GE3126, coupled with practical implementation of an imaging instrument may be an important step forward in preventing nerve damage in the operating room.

Intraoperative fluorescence imaging of peripheral and central nerves through a myelin-selective contrast agent

Purpose

Patients suffer from complications as a result of unintentional nerve damage during surgery. We focus on improving intraoperative visualization of nerves through the use of a targeted fluorophore and optical imaging instrumentation.

Procedure

A myelin-targeting fluorophore, GE3111, was synthesized, characterized for its optical and myelin-binding properties using purified myelin basic protein, and evaluated in mice. Additionally, a compact instrument was adapted to visualize nerves.

Results

GE3111 was synthesized using a versatile methodology. Its optical properties were sensitive to the local environment both in vitro and in vivo. Following intravenous injection, central and peripheral nerves were visualized, with the kinetics of nerve uptake modifiable depending on the formulation. Fluorescence polarization showed specific and strong binding to purified myelin basic protein. Nerves were visualized in vivo using a dedicated compact imaging device requiring less than 2.5 mW/cm² of illumination at 405 nm.

Conclusions

Fluorescence imaging of nerves through myelin showed a potential for use in image-guided surgery. Intraoperative nerve imaging is an example where contrast agent and instrument development come together as a result of clinical need.

Electronic supplementary material

The online version of this article (doi:10.1007/s11307-012-0555-1) contains supplementary material, which is available to authorized users.

Dual-mode laparoscopic fluorescence image-guided surgery using a single camera

Iatrogenic nerve damage is a leading cause of morbidity associated with many common surgical procedures. Complications arising from these injuries may result in loss of function and/or sensation, muscle atrophy, and chronic neuropathy. Fluorescence image-guided surgery offers a potential solution for avoiding intraoperative nerve damage by highlighting nerves that are otherwise difficult to visualize. In this work we present the development of a single camera, dual-mode laparoscope that provides near simultaneous display of white-light and fluorescence images of nerves. The capability of the instrumentation is demonstrated through imaging several types of in situ rat nerves via a nerve specific contrast agent. Full color white light and high brightness fluorescence images and video of nerves as small as 100 µm in diameter are presented.

Compact Fluorescence and White Light Imaging System for Intraoperative Visualization of Nerves

Fluorescence image guided surgery (FIGS) allows intraoperative visualization of critical structures, with applications spanning neurology, cardiology and oncology. An unmet clinical need is prevention of iatrogenic nerve damage, a major cause of post-surgical morbidity. Here we describe the advancement of FIGS imaging hardware, coupled with a custom nerve-labeling fluorophore (GE3082), to bring FIGS nerve imaging closer to clinical translation. The instrument is comprised of a 405 nm laser and a white light LED source for excitation and illumination. A single 90 gram color CCD camera is coupled to a 10 mm surgical laparoscope for image acquisition. Synchronization of the light source and camera allows for simultaneous visualization of reflected white light and fluorescence using only a single camera. The imaging hardware and contrast agent were evaluated in rats during in situ surgical procedures.

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.

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.

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.

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.

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.

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.

Prevention and management of erectile dysfunction following radical prostatectomy

Most studies indicate general satisfaction rates of greater than 80% after radical retropubic prostatectomy. Nonetheless, erectile dysfunction remains the most common problem postoperatively, with rates ranging from 100% to 10% depending on the experience of the surgeon, the frequency with which he or she performs the surgery, the nerve-sparing nature of the procedure, the stage of the disease, and the age and preoperative potency of the patient. The natural recovery of erection function takes as long as 24 months and can be expedited by early treatment with intracorporal injection therapy. The treatment of erectile dysfunction after radical retropubic prostatectomy is highly successful despite the finding that fewer than 50% of patients seek treatment. Sildenafil does not seem to be effective early in the recovery phase but increases in efficacy as the nerves recover from intraoperative injury. Other modalities in the early recovery phase in the order of increasing effectiveness are intraurethral prostaglandin, the vacuum erection device, and intracorporal injection therapy. After 2 years from surgery, the recovery of natural function and improved sildenafil responsiveness are unlikely, and the implantation of a prosthesis is reasonable if other modalities are ineffective or unacceptable for the patient. Animal studies and human trials are underway to examine ways to expedite and maximize the return of erectile function.

Interventional neurophysiology of the sacral nervous system

Clinical neurophysiological tests have been introduced for the sacral neuromuscular system to aid with diagnosis of neurogenic conditions involving the lower urinary tract, anorectal and sexual dysfunction. The tests have, however, the potential to be of value in different interventions outside of the neurophysiological laboratory. EMG monitoring can be used for exact application of botulinum toxin by the relatively non-invasive transcutaneous approach in treatment of male detrusor sphincter dyssynergia. Checking for compound muscle action potentials of the external anal sphincter is proposed as the best method for exact placement of wire electrodes close to the 3rd sacral roots in treating lower urinary tract dysfunction by 'neuromodulation'. Presently the most established use of clinical neurophysiological techniques--outside the laboratory--as related to the sacral neuromuscular system is in the operating theatre. These tests have been introduced to identify relevant structures, for instance pudendal afferents within dorsal sacral roots, which should be spared during rhizotomy procedures for treatment of spasticity. Modified techniques are used intraoperatively to monitor the integrity of the lower sacral reflex arc (the bulbocavernosus reflex) or the lower sacral afferents throughout the spinal cord (pudendal SEP). Clinical neurophysiological tests are expected to become established in several interventions involving the sacral neuromuscular system.

A simple and reliable monitoring system to confirm the preservation of the cavernous nerves

BACKGROUND

It is important to establish a procedure with which to confirm the preservation of the cavernous nerves during nerve-sparing radical surgery. For this purpose, we examined changes in intracavernous pressure (ICP) following electrical stimulation of the neurovascular bundle (NVB) with respect to the continuity of the cavernous nerves.

METHODS

Six cases of radical prostatectomy and eight cases of radical cystoprostatectomy were examined. In all cases, prior to prostate removal, electrical stimulation of the site where the NVB was determined to run was performed and the changes in ICP measured. In eight cases, ICP changes were also measured following prostate removal.

RESULTS

Prior to prostate removal, ICP changes could be measured in all 28 sides of 14 cases. These changes were classified into two patterns: stimulation-related increases of convex waveform (t1) were observed in 24 sides (85.7%); and waveforms with reversed type (t2), which was thought to be an incomplete type t1, were observed in four sides (14.3%). There were no ICP changes following non-sparing or incomplete sparing of NVB macroanatomically. Of five sides where the NVB was supposedly completely preserved macroanatomically, ICP changes consisted of type t1 on three sides, t2 on one side and type t2 or no change on a single side. All measurements were obtained within 10 min. Neither electrical stimulation nor measurement of ICP caused any adverse effects.

CONCLUSION

Intraoperative stimulation of the NVB while monitoring ICP changes provides a simple and reliable method of accurately evaluating the preservation of the cavernous nerves.

Neurologic erectile dysfunction

Neurologic erectile dysfunction presents a diagnostic and treatment challenge to the internist and urologist. Multiple chronic disease modalities and traumatic etiologies exist. Education regarding these conditions and a detailed and thorough history and office work-up are the best resources for the clinician. Treatment can follow the model of proceeding from the least to most invasive procedure (process of care), taking into account patient and partner satisfaction. Because the psychology of grief and loss may enter into treatment of some neurologic conditions (e.g., erectile dysfunction after radical retropubic prostatectomy, spinal cord injury, or chronic diseases), a whole-patient approach encompassing psychotherapy is warranted.

Intraoperative cavernous nerve stimulation during nerve sparing radical prostatectomy: how and when?

Although nerve-sparing prostatectomy is widely practiced, the results with respect to potency preservation often do not meet expectations. The concept of intraoperative cavernous nerve stimulation is rational. Recent data that link the response to sildenafil after prostatectomy to bilateral nerve sparing has increased the importance of optimizing nerve sparing. The cavernous nerves are often difficult to visualize and may have a variable course. A tumescent response to nerve stimulation can be consistently demonstrated. The response may be subtle, and characterized by a minimal increase in penile circumference and blood flow. Immediately after prostectomy, proximal nerve stimulation identifies whether neural continuity has been maintained, and is predictive of recovery of erectile function. A new device, the Cavermap, has been developed to permit intraoperative nerve stimulation with tumescence monitoring. An initial phase 2 and subsequent phase 3 single blinded, randomized, multicenter study that compared Cavermap-assisted prostatectomy with conventional nerve sparing demonstrated a significant benefit in terms of the duration of nocturnal tumescence by Rigiscan (Timm Medical Technologies, Eden Prairie, Minnesota) at 1 year. Other approaches are being explored, including sural nerve grafting, use of nerve stimulation during cystectomy or abdominal-perineal resection, and direct corpus cavernosum pressure monitoring during nerve stimulation. These approaches warrant further evaluation.