Erectile Dysfunction after Robot-assisted Radical Prostatectomy

Marcelo A Orvieto; Rafael F Coelho; Sanket Chauhan; Mary Mathe; Kenneth Palmer; Vipul R Patel

Disclosures

Expert Rev Anticancer Ther. 2010;10(5):747-754. 

In This Article

Methods

A review of the literature was performed for all published manuscripts between 2000 and 2009 using the keywords 'robotic radical prostatectomy', 'robot-assisted radical prostatectomy', 'nerve sparing', 'cavernosal nerve' and 'potency outcomes', using the Medline database. Only studies published in English were included. Comparative and noncomparative studies were included. Outcomes were tabulated and analyzed from the resulting articles. Weighted means were calculated for number of patients, age, and potency rates and for bilateral NS (BNS). Manuscripts were selected according to their relevance to the current topic (i.e., original articles, number of patients in the series, prospective data collection) and incorporated into this review.

Anatomy of the NVB

The modern concept of the NVB comes from the studies by Walsh et al..[6] Using male fetus and newborn first and then a 60-year-old human cadaver,[20] they demonstrated that the corpora cavernosa are innervated by branches coming from the hypogastric plexus located between the rectum and the urethra, and penetrate the urogenital diaphragm posterolateral to the urethra. As such, the NVB is a tubular structure that runs posterolateral to the prostate as an inferior extension to the pelvic hypogastric plexus. Based on these findings, Walsh and his team proposed modifications to the RP procedure known at that time[21] where the lateral pelvic fascia was incised anterior to the NVBs, and the lateral pedicles are divided close to the prostate to avoid injury to the NVB that gets tented up at the base of the prostate. This marked a new era in the treatment of CaP where the benefits outweighed the risks for the then highly invasive procedure of RP.

More recently, Costello et al. in 2004 using human cadavers demonstrated that most of the NVB descends distally and dorsolaterally to seminal vesicles (posterior nerves), while anterior nerves course along the posterior–lateral border of seminal vesicles (Table 1).[22] The anterior and posterior nerves of NVB run distally towards the apex, converge at midprostatic level and then diverge again as they approach the prostate apex, where it is most variable in course and architecture. Additionally, Costello suggested a functional organization of the NVB in which the anterior portion included mostly fibers innervating the prostate, the posterior portion with mostly fibers supplying the rectum and a midportion, the true cavernosal nerves. Similar findings to those described by Costello were reported by Tewari et al. in their study on male cadavers and review of video-taped cases from 200 men undergoing RARP.[23] The authors described the presence of a 'tri-zonal neural architecture' comprised of a predominant NVB (PNB) or classic nerve bundle plus two more areas: a proximal neurovascular plate closely related to the posterior bladder neck and seminal vesicles, and accessory neural pathways located between the layers of lateral pelvic fascia posterolateral and anterolateral to the prostate. This network of nerves seem to carry neural impulses to the erectile tissue outside the classical PNB and may play a crucial role in preservation of potency postoperatively.

Significance of Fascial Planes during Nerve Preservation

The endopelvic fascia is a multilayer fascia that covers the prostate and bladder, and is linked to the prostate capsule by collagen fibers, finally inserting in the form of puboprostatic ligaments to the pubic bone.[24] Laterally, the endopelvic fascia divides into the so-called prostatic fascia that stays in direct continuity with the true prostatic capsule, and an outer layer or lateral pelvic fascia. In close proximity to the tips of the seminal vesicles, autonomic fibers originating from the caudal portion of the pelvic plexus, known as the cavernous branches, form a dense neurovascular network and travel in a direct route from the pelvic plexus towards the posterolateral base of the prostate, gradually coalescing into a more organized bundle, approximately 6 mm wide at the level of the prostate.[25] At this point, these branches travel along the postero-lateral aspect of the prostate towards the apex and membranous urethra, embedded in between the different layers of the lateral prostatic fascia. Studies from Kiyoshima et al. demonstrated that the NVB was localized near the posterolateral region in only 48% of the cases.[26] In the remaining 52%, the nerves were spread on the entire lateral aspect of the prostate without either specific localization or bundle formation. Moreover, Kiyoshima described that the site and the localization of NVB is related to the degree of fusion between prostate capsule and lateral pelvic fascia.[26]

Although the knowledge of a NVB-embedded multilayered fascia is not new, and concepts such as extrafascial and intrafascial NS were introduced a decade ago for open RP,[27] the high magnification offered by the laparoscopic environment first and then the robotic platform, has allowed the surgeon to better visualize these layers intraoperatively and utilize previous anatomical knowledge to perform a more precise nerve preservation. Indeed, different techniques and refinements for intrafascial, interfascial and extrafascial nerve preservation have become widespread, gaining acceptance among surgeons performing RP.[24,28]

An intrafascial plane is the plane between the prostatic capsule and the inner layer of the prostatic fascia. During an intrafascial dissection, the endopelvic fascia is incised only ventrally, medial to the puboprostatic ligaments.[24] The interfascial plane is the plane between the prostatic fascia and the lateral pelvic fascia. Posteriorly, the interfascial plane exists as the avascular plane between the prostatic fascia and the Denonvilliers fascia and between the prostatic fascia and the anterior extension of Denonvilliers fascia. Most of the NVBs lie between the anterior extension of the Denonvilliers fascia and the levator fascia. Hence complete preservation of NVBs is achieved with either intrafascial or interfascial dissection. Dissection along the extrafascial plane is right through the NVBs and might enable some preservation of the neural tissue or none.

Surgical Technique

Although debatable, it appears that adequate surgical technique during NVB preservation not only leads to successful recovery of erections in patients with good sexual function preoperatively, but may also improve overall continence outcomes.[29] Thus, every attempt should be made to preserve the NVBs. The dilemma is that undue NS might lead to increased positive surgical margin (PSM) rates, especially posterolateral and apical margins. Thus a tailored NS procedure is necessary for each patient, based on individual preoperative variables[30] as well as intraoperative findings. Besides recognizing the correct surgical planes of dissection, several technical aspects of the dissection are key for achieving good potency outcomes after RARP.

A very important aspect during the NS procedure is the use of energy. Dissection has to be carried out without any form of thermal energy in order to avoid damage owing to direct burning or lateral spread. These nerves are non-myelinated, making them extremely vulnerable to thermal energy. Ong et al., using a canine model, demonstrated that the use of monopolar or bipolar sources in the vicinity of the prostate during dissection of the NVB was clearly associated with a significantly decreased erectile response to cavernous nerve stimulation.[31] In a clinical study of patients undergoing RARP, Ahlering et al. compared potency outcomes between patients who underwent NS using electrocautery versus a group without cautery. In the cautery group, 16.7% of patients undergoing BNS were potent after 9 months and 67.9% at 24 months, compared with 72.8 and 92% for the cautery-free group, respectively.[16] In another 2-year prospective follow-up study from the same group, the authors confirmed their previous findings of improved return of potency function among patients who received cautery-free NS. In this study, the authors also demonstrated that unilateral NS (UNS) (i.e., loss of 50% of the nerve volume) was associated with only a 1.15–1.36-times loss of overall potency function compared with BNS (UNS 50% vs BNS 68% for the group where cautery was used and UNS 80% vs BNS 93% where cautery-free technique was used). Furthermore, the quality of erections (as estimated by the International Index of Erectile Function [IIEF]-5) did not vary with the degree of NS, suggesting an important role of neural 'crossover'.[17]

Damage to the nerves might also be caused by the method of handling of the pedicles, which are very closely related to NVBs. These pedicles can be controlled by clamping, clipping or suturing. In this regard, Ahlering et al. described an approach to NS using vascular clamps and suture ligation of the pedicles.[32] After the posterior dissection is completed and the prostate is released from its posterior attachments, the vascular pedicles are controlled using laparoscopic bulldog clamps. The pedicles are ligated using a running 3–0 polyglycolic acid suture and clamps are then removed. Dissection continues antegrade, strictly athermally beyond this point and the suture is used to control remaining vessels along the length of NVBs. Using this technique, the authors reported return of potency of 40% at 3 months and 80% at 2 years for those who had UNS, while for BNS the rate was 29.3 and 93%, respectively.[33] Similar results were reported by the Cleveland Clinic group also using a 'bulldog technique' when performing laparoscopic radical prostatectomy (LRP).[34]

Dissection of the NVB can be performed from the prostate base to apex (antegrade) or from apex to base (retrograde), unilateral or bilateral, partial or full. Traditionally, NS during laparoscopic and robotic prostatectomy has been performed in an antegrade fashion. This approach allows for early control of the prostatic pedicles, thus minimizing blood loss. Additionally, the antegrade approach provides a more natural working angle for instruments during NVB dissection after the bladder neck has been divided. The drawback to this technique is that as the NVB is tented up at the base of the prostate, its precise course is not well visualized with the potential risk of exerting excessive traction, trauma or unintended transection of the NVB. Patel et al. developed a hybrid technique in which retrograde, early release of the NVB is performed before the pedicle is transected, allowing for clear visualization of the NVB pathway followed by antegrade prostatectomy.[35] The lateral pelvic fascia is incised at the midportion of the prostate and an avascular plane is developed between the NVBs and the prostatic fascia. This plane is extended posteriorly until it meets the interfascial plane developed initially between the prostate and the rectum. The entire dissection is carried out athermally. The vascular pedicles are controlled with hemo-lock clips. Using this technique, the authors reported on 397 consecutive patients with preoperative SHIM score higher than 21 and at least 3 months follow-up. Potency was defined as having erections sufficient for penetration with or without the use of phosphodiesterase (PDE)-5 inhibitors. In these patients, 87.7% were potent.[36]

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