Nerve sparing in robot-assisted radical prostatectomy: Tips and tricks

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:

• Grade 1 NS is developed through the plane just outside the prostatic capsule ( Fig. 15.2 )

  

• 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.

• 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.

• 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.