Introduction
Robot-assisted radical prostatectomy (RARP) is the most common form of treatment for localized prostate cancer. Introduction of robotics has helped to visualize prostatic and periprostatic structures better and improve the ability to perform detailed dissections. Still, a significant number of men experience erectile dysfunction (ED) and urinary incontinence (UI) after RARP. The rates of UI (defined as usage of at least one pad/24 hours) after a year from RARP range from 4% to 31%, while the rates of ED have been reported as high as 94%. Consequently, efforts are ongoing to decrease these drawbacks that may severely affect patients’ quality of life.
Although post-prostatectomy ED and UI etiology are multifactorial, surgical factors play an important role.
Before we embark on the procedure, nerve sparing during robotic prostatectomy hinges on the following preoperative questions: (1) What is the risk of extracapsular extension (ECE) that could result in a positive surgical margin (PSM); and (2) if minimal ECE is expected, could we still save some of the lateral nerves while achieving negative margin? These questions are best addressed in our prior papers describing side-specific ECE risk and matching grades of nerve sparing to achieve the negative margin while saving what we can—incremental nerve sparing.
During the procedure, optimal nerve sparing requires an appreciation of the complexity of the nerves—(1) embracing hammock neural architecture and (2) appreciating “layers within layers” in the periprostatic tissue concept.
Neural hammock
Comprehension of the pelvic anatomy is vital in achieving satisfactory functional and oncologic outcomes. The balance between the risk of ECE and NS is the key to a successful procedure.
Anatomical studies have shown a complex periprostatic neurovascular distribution that extends beyond the traditional posterolateral position described by Walsh and Donker. Tewari et al. described the “neural hammock,” a structure composed of (1) the proximal neurovascular plate (PNP), located lateral to the bladder neck, seminal vesicles (SVs), and branches of inferior vesical vessels; (2) the predominant neurovascular bundle (PNB), found within the layers of the lateral pelvic fascia and levator fascia, and (3) the accessory neural pathways (ANP), situated anterolaterally to the prostate. , Parasympathetic, sympathetic, and somatic nerves run within the neural hammock. While their exact distribution remains under exploration, understanding the available anatomic studies will have an impact on functional outcomes, especially erectile function (EF). Costello et al. found parasympathetic innervation in the anterior zone between 3 o’clock and 9 o’clock; these fibers only represented around 14% to 23% of parasympathetic fibers compared to the amount located in the posterolateral zone. Additionally, Sievert et al. reported the results of immunohistochemical staining and diffusion tensor imaging (DTI). This study confirmed a wide distribution of parasympathetic nerves, mainly located posterolateral at the midsection, posterior to posterolateral at the apex, and anterior to posterolateral at the base. It is important to notice that the autonomic and somatic innervation provided by these periprostatic nerves to the prostatic apex and urethral sphincter also plays a major role in urinary continence (UC).
Innervation to the urethral sphincter travels through the pudendal nerve or the pelvic plexus. There are two pudendal pathways—extrapelvic branches and intrapelvic branches. The former fibers penetrate the prostatic urethra at 9 to 12 o’clock and 1 to 3 o’clock close to the prostatic apex, while the intrapelvic branches of the pudendal nerve penetrate the external urethral sphincter (EUS) at 5 and 7 o’clock. Some somatic fibers run with the autonomic nerves, mainly in the posterior surface of the bladder and the anterolateral surface of the US. The posteromedial aspect of the prostatic apex receives innervation from the same fibers that provide autonomic innervation to the urethra and its sphincter. These nerve fibers, covered by the levator fascia, originate from the most caudal edge of the inferior hypogastric plexus (IHP) or from the neurovascular bundle (NVB) itself. Moreover, some neural fibers reach out, piercing the supporting skeletal and fibrous structures. The levator ani fascia acts as a boundary between intrapelvic and extrapelvic branches at a distance of 5 mm from the sphincteric branch. This supports the need for careful dissection while approaching the levator ani muscle after the levator ani fascia opening in grade 3 NS. The extrapelvic somatic sphincteric branches enter the EUS at a distance ranging from 4 to 11 mm, having a risk of damage during apical dissection. Therefore, the preservation of periprostatic nerves is not only important for erectile function (EF) but for UC as well ( Fig. 15.1 ).
Layers within the lateral prostatic fascia
Nerve fibers run intermingling surrounding the prostate, extending from the anterolateral to the posterolateral prostatic surface. The majority of fibers are enclosed between the prostatic capsule and lateral prostatic fascia, followed by some fibers intermingled between the layers of the lateral prostatic fascia and a few fibers between the lateral prostatic fascia and levator ani fascia.
Layers of the periprostatic fascia fuse with the anterior layer of Denonvilliers’ fascia to form a triangular area that surrounds the PNB. The prostatic fascia constitutes the medial wall of the triangle, while the lateral wall is formed by the lateral pelvic fascia and the posterior wall by the anterior layer of the Denonvilliers’ fascia. Taking into account this distribution pattern, Tewari et al. described grades of NS using the venous layer as the main landmark:
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Grade 1 NS is developed through the plane just outside the prostatic capsule ( Fig. 15.2 )
Fig. 15.2
Grade 1 Nerve Sparing.
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Grade 2 NS, this plane is located between the perivenous layer and the lateral prostatic fascia. On the posteror surface of the prostate, the incision is made through the Denonvilliers’ fascia while ensuring that the deeper layers surrounding the rectum are not affected.
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Grade 3 NS can be identified between the lateral prostatic fascia and levator ani fascia. In this case, all layers of Denonvilliers’ fascia are excised.
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Grade 4 corresponds to a non-nerve sparing approach
A decision about NS to be performed is based on oncological variants such as prostate-specific antigen (PSA), data from the multiparametric magnetic resonance imaging (mpMRI) of the prostate, and Gleason score/Grade Group. , This risk-stratified approach has demonstrated superior outcomes in terms of UC and EF. In our institution, we use the nomogram developed by Martinini et al., which allows a side-specific nerve-sparing surgery, tailoring the procedure according to MRI, PSA, and biopsy findings.
Other landmarks have been described during NS approaches; for example, Schatloff and colleagues have described the identification of landmark arteries to aid in NS approaches. Their system includes five grades of NS, with grade 1 representing a non-NS approach, and grade 5 representing a complete NS.
Apical dissection
This is one of the most challenging steps during the surgery. At this level, nerves, muscles, vessels, and fasciae are closely related. Consequently, millimeters can make a difference in functional results and proper cancer resection since PSMs are commonly found in this zone. Different techniques focused on achieving a fully functional urethral length (FFUL) while preserving the neural hammock and avoiding PSM have been explored. Urethral length preservation has been shown to improve postoperative continence rate and shorter time to achieve continence. In fact, Schlomm et al. described an individualized apical preparation to preserve FFUL. This FFUL technique, along with preservation of the anatomical fixation of the urethral sphincter, achieved 50% of continence in 1 week. Our retroapical technique of synchronous urethral transection enabled better visualization of the intersection between the prostatic apex and the membranous urethra. This technique facilitated precise dissection of the apex and optimized membranous urethral length preservation. A thirty-degree upward-facing lens optimized visualization of the apical junction during retroapical dissection. Similarly, Bianchi et al. described the dissection of the urethra 2 to 3 mm from the apex of the prostate, the “collar” technique, to reduce the positive rates of the apical margin with maximum preservation of the membranous urethra. As recently demonstrated by Nyangoh Timoh et al., the innervation of the urethra can be found in the perirectal and lateroprostatic zones enclosed in a triangle limited by the urethra, rectum, and levator ani muscle. These nerves can arise from the PNB itself, innervating the internal and external sphincters as well as the erectile bodies. Therefore, apical dissection must be done with optimal visualization, assuring a bloodless field to accomplish the precise tumoral excision while achieving functional and structural preservation.
Tips and tricks to perform a nerve-sparing procedure
Careful surgical planning
Integration of imaging has been demonstrated to be useful in preoperative assessment. In our institution, side-specific nomograms were developed to determine the risk of extracapsular extension (ECE) and seminal vesicle invasion (SVI) based on mpMRI findings and clinical parameters. , , Planning the surgery with these tools allows the implementation of a tailored incremental NS, achieving better functional and oncologic outcomes. Recently, the combination of preoperative gallium-68 prostate-specific membrane antigen positron emission tomography/computed tomography (68Ga-PSMA PET/CT) PSMA, mpMRI, and clinical parameters showed an added value for detecting lymph node metastasis compared to the traditionally available nomograms (e.g., MSKCC, Briganti, CAPRA). The aforementioned may have implications in the selection of patients who really benefit from ePLND, avoiding unnecessary complications, including PNP injury.
Traction free and athermal dissection to preserve the neural hammock ,
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The neurovascular hammock is attached predominantly at the posterolateral aspect of the prostate and less prominently at the anterolateral surface of the prostate. An early release of the neurovascular hammock minimizes traction while controlling the lateral pedicles during the posterolateral dissection of the prostate. This again facilitates the NS procedure with minimal damage.
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Avoid extreme lateral dissection during posterior bladder neck transection due to possible injury to the PNP.
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Identify the retrotrigonal layer and perform a careful dissection of the vas deferens and SVs. To avoid PNP and hypogastric branch injury, identify the medial avascular plane during SV dissection and control their blood supply with clips, especially at their tips ( Fig. 15.3 )
