Anatomy and mechanisms of male urinary continence

The prostate is located surrounding the proximal part of the male urethra and it is adjacent to several anatomical structures that are involved in maintaining UC and responsible for erectile function. As a result, the wider the resection to ensure the oncological outcome, the greater the risk of impairing UC due to inadvertent damage to surrounding tissues. Considering the close involvement of periprostatic structures in UC, in most patients, incontinence occurs early and is followed by gradual recovery over time.

Although the mechanisms of UC in males are not completely understood, alongside advances in volumes and techniques of radical prostatectomy, a large amount of related anatomical knowledge has been recently accumulated. Currently, male UC is considered as the combined actions of multiple anatomical structures surrounding the prostate gland ; together, these structures constitute the urethral sphincter complex and are summarized below:

• 1.
  

  The smooth muscle sphincter (lissosphincter) consists of two layers (inner longitudinal and outer circular) and is innervated by the autonomous nervous system. It forms a spongy structure below the urethral mucosa, and external contraction completely cuts off the urine flow.

  
  
• 2.
  

  The stratified sphincter (rhabdosphincter; the posterior part forms the median fibrous raphe [MFR] with no muscle layer) is responsible for the slow-twitch, passive control. It forms a cylindrical shape that originates from the prostate apex and attaches to the deep, transverse perineal muscles. In the transverse cross-section, the muscle in the stratified sphincter is distributed in an omega shape; posteriorly, there is no muscle, but instead, forming the MFR are dense fibrous tissues. The MFR forms a posterior support complex by connecting the central tendon posteriorly and Denonvilliers’ fascia superiorly.

  
  
• 3.
  

  The puboperinealis muscle is responsible for fast-twitch, active control. It forms the medial part of the levator ani muscle. In the coronary view of magnetic resonance imaging, the puboperinealis muscle appears as two teardrop shapes running bilaterally, lateral to the urethra. As it attaches to the perineal body posterior to the urethra, the puboperinealis muscle ultimately forms a structure that supports the urethra.

Based on this understanding of the urethral sphincter complex, widespread efforts have been made to mitigate UI by identifying and preserving this complex during surgery. Conceptually, these techniques can be summarized as the preservation of the internal/external sphincters and reconstruction of anterior/posterior support structures.

Urethrovesical anastomosis

The greatest change and development with the introduction of RARP was, first, that a safe and complete urethrovesical anastomosis became possible as compared to open or laparoscopic approaches, and this change has led to a decrease in the incidence rates of urine leakage and urethral strictures at the urethrovesical anastomosis or bladder neck contracture, which were previously common in the era of nonrobotic prostatectomy.

In the era of robotic surgery, while there are several technical modifications by the surgeon’s preference, a continuous stitch that distributes tension broadly across multiple points along the bladder neck and urethra utilizing two separate sutures tied together at their ends, which was originally described by van Velthoven et al., became the most typical way. To prevent the suture from slipping and thereby maintaining tissue approximation, double-armed barbed sutures are used to accomplish this step. The introduction of unidirectional barbed absorbable polyglyconate thread—armed with a surgical needle at one end and a welded-loop end effector at the other—challenged the previous Monocryl monofilament and Vicryl braided sutures. A meta-analysis was published in 2015 and concluded that barbed sutures could significantly reduce anastomosis time, operative time, and posterior reconstruction (PR) time. However, possible complications deriving from the use of barbed sutures (such as intraoperative leakage/urethral tear and its management, erosion and bladder neck contracture) have not been addressed.

Bladder neck preservation

The bladder neck includes the intravesical sphincter; in open surgery, a broad incision and dissection of the bladder neck are performed to allow complete dissection of the prostate base, followed by suture ligation to restore the original thickness. However, the proximal internal urethral sphincter, previously referred to as the internal sphincter, has been reported to play a role in UC. In a systematic review of 13 studies on this topic, 1130 patients in whom the bladder neck was spared were compared with 1154 control patients, and the former showed a significant improvement in the rate of UC at both 6 and 12 months of follow-up. However, bladder neck sparing is not possible in all patients, especially in those who have had previous surgery for benign prostate obstruction or in patients with a medial lobe; in these cases, proper reconstruction of the bladder neck after resection is crucial.

Neurovascular bundle preservation

The preservation of the NVB is intended to facilitate early recovery of erectile function rather than to prevent incontinence. However, preservation of the NVB is consistently reported to help recovery from UI. Ko et al. analyzed 1299 patients operated by a single surgeon using the same technique and found that recovery from proton pump inhibitors (PPIs), defined as 0 pad usage within 3 months, was significantly earlier in patients for whom the NVB was even partially spared than in patients with no NVB preservation. A recent systematic review also found an association between NVB preservation and recovery from UI. The relationship with continence may be mainly due to the dissection technique and lack of thermal energy/traction used during nerve-sparing surgery and not due to the preservation of the nerve bundles themselves. It should be remembered that a complete NVB preservation is not always feasible for oncological reasons; however, preservation of the NVB, even partially, is likely important to achieve UC.

Techniques for apical dissection and anterior preservation

A modified technique of apical dissection with endopelvic fascia preservation has been recently described. The technique aims to preserve as maximal as possible the apical complex and periurethral tissues, together with the preservation of the NVB untouched and covered. The authors performed a propensity score matching with a similar group who underwent conventional RARP (104 patients in each group) and found that the modified technique yielded significantly faster continence (mean 46 vs. 70 days) and potency recovery (mean 74 vs. 118 days).

Another preservation approach recently delivered is the “Hood technique,” which includes the sparing of periurethral anatomic structures in the space of Retzius but starts with an anterior approach. The detrusor apron, puboprostatic ligament complex, arcus tendineus, endopelvic fascia, and a pouch of Douglas remain untouched. Wagaskar et al. reported an early return of continence without compromising positive surgical margin (PSM) rates. Exclusion of the anterior tumor location may contribute to a reduction in PSMs. Summarizing, recent literature is moving toward preserving the anterior/apical compartment to improve UC.

Reconstructive techniques

Radical prostatectomy results in the discontinuation of periprostatic structures and mechanisms underlying UC. It shortens the urethral length and reduces bladder-outlet resistance; RARP may hinder bladder-neck sphincteric function and changes the structure and function of the urinary sphincteric complex. As anatomical knowledge about the prostate gland increased, the importance of the posterior supporting structures, particularly the posterior support complex, has received greater attention. PR has become a major milestone in modern prostate surgery; this procedure is also called the Rocco stitch, named after the surgeon who first introduced the concept of reconstructing the posterior structures that are damaged or lost while operating on the prostate. Patel et al. extended this concept to include anterior reconstruction (AR), as the role of the puboprostatic ligament, superior to the prostate apex, is also important in supporting the urethra. Recently, the usefulness of the so-called total anatomical reconstruction has been reported, in which the prostate apex is divided into five anatomical units, each of which is reconstructed.

PR represents a cornerstone in radical prostatectomy. As a result of prostatectomy, the posterior supportive layers of the bladder and prostate are divided, including Denonvilliers’ fascia and its confluence with the posterior rhabdosphincter. Thus, the reconstruction of these supportive structures has been attempted. Several suggested mechanisms for PR include re-establishing the posterior anatomic support to the bladder and urethra, improving urethral coaptation during voiding, reducing tension at the vesicourethral anastomosis, and increasing the functional length of the striated urethral sphincter complex. ^,

The role of PR in terms of earlier continence recovery has been widely studied across time. While several technical modifications from the original concept should be considered, two initial randomized trials with some technical modifications have found no significant benefits in the earlier regain of continence. ^, Nevertheless, a recent meta-analysis on the published series, including the other randomized trial, demonstrates that the implementation of PR during radical prostatectomy improves early continence recovery at 3 to 7, 30, and 90 days after catheter removal, while the continence rate at 180 days was not clinically affected. Another meta-analysis involved 32 studies for a sample size of 4697 patients and considered the impact of each pelvic floor reconstruction technique. Nineteen trials evaluated the efficacy of PR, seven trials evaluated the efficacy of anterior suspension (AS), four trials evaluated the efficacy of PR + AR, and two trials evaluated the efficacy of PR + AS. Seven of these trials were randomized controlled trials (RCTs). Pooled results of patients who had PR demonstrated complete UC improvement at 1 to 4, 28 to 42, 90, 180, and 360 days following catheter removal. AS was associated with improvement at 28 to 42 days. The PR + AR was associated with UC at 1 to 4, 90, and 180 days. Patients who underwent PR had the least UI. Furthermore, pooled data from six trials showed that PR was associated with the least amount of cystogram leakage after surgery (RR = 0.37; P = .004).

The recognized advantage of PR is to reduce the distance between the bladder neck and the urethra, allowing for tension-free vesicourethral anastomosis. Moreover, the evidence does suggest that the incidence of pelvic hematoma may be reduced by performing a PR.

Maximal preservation of the urethral length

Ahlering et al. found that the remaining length of the urethra after resection of the prostate apex is of paramount importance for UC recovery. In the dissection of the prostate apex, the final stage of prostatectomy, systematic dissection of the urethra before completely isolating the prostate is crucial to ensure enough urethral length. However, given that the apex is not covered by the prostate capsule, its management should be performed carefully; in case of cancer developing in this area, apical dissection as close to the urethra as possible is recommended to avoid the risk of PSM in this location.

Different access: The retzius sparing approach

Conventionally, RARP requires access to the Retzius space, potentially disrupting some anatomical structures contributing to the UC mechanism. In 2010, Galfano et al. described the Retzius sparing RARP (RS-RARP) through the Douglas space: the approach maintains the integrity of structures of the anterior compartment—NVBs, pubourethral or puboprostatic ligaments, Aphrodite’s veil, accessory pudendal arteries—and carries the perspective of improved and earlier recovery of continence and erectile function. The first prospective trial by authors reported over 90% of immediate UC and a 70% rate of erectile function at 1 year.

Since then, the RS has been one of the most studied approaches, with four meta-analyses currently available. Phukan et al. performed a systematic review and meta-analysis involving two RCTs and four nonrandomized prospective comparative studies for an overall amount of 638 patients included. RS robot-assisted laparoscopic radical prostatectomy (RALP) was associated with better early continence rates (≤1 month) (moderate quality evidence) (RR 1.72; 95% CI 1.27, 2.32; P = .0005) and at 3 months (low quality evidence) (RR 1.39; 95% CI 1.03, 1.88; P = .03).

Dirie et al. reported similar conclusions but included in the meta-analysis most low evidence studies. Another meta-analysis from Jiang et al. included 8 studies (2 RCTs, 3 retrospectives, and 3 prospectives) for a total of 1620 patients and concluded for improved UC rates with the RS-RARP compared to the non-RS-RARP.

Margin status represents the major concern of the RS approach. The meta-analysis from Tai et al. confirmed better and faster UC recovery with RS but significantly higher PSM rates (OR 1.68; P = .02). Specifically, higher PSM rates were reported for the anterior site (OR 4.34; P = .03) and for the subset of RCT (OR 2.80; P = .007). The limited view of surgeons performing RS-RARP in the anterior aspect may explain the higher PSM rates at this site while similar in other regions. A Cochrane analysis pooled data from five unique RCTs (two published, one in press, and two abstract proceedings) for an overall amount of 571 randomized participants. The analysis confirmed that RS-RALP probably improves continence within one week after catheter removal (RR 1.74) and may increase continence at three months (RR 1.33). The effects of RS-RALP on potency remain uncertain, whereas RS-RALP may increase PSM rates (RR 1.95).

In conclusion, current evidence suggests that the RS approach is feasible and may lead to better and earlier UC recovery. However, PSM remains an unsolved concern, and the approach is still considered challenging in the case of anterior tumors, in post-TURP patients, in the case of high-volume PCas, or in the presence of median lobes.