Inflatable penile prosthesis in the radical prostatectomy patient: a review

In the population of patients with prostate cancer, survivorship has come to the forefront of continuity-of-care. In addition to urinary control, erectile function is a significant issue after radical pelvic surgery. Penile prosthesis surgery remains an excellent option for restoring erectile function to those for whom more conservative measures have failed. This review article outlines the anatomical, surgical and post-operative consideration involved in the placement of a penile prosthesis in this special patient population.


Erectile dysfunction (ED) rates after radical prostatectomy (RP)
Penile erection is the culmination of complex series of highly integrated phenomena involving the central nervous system, peripheral nervous system, endocrine system and the vascular system. These systems must be working in concert and at a high level in order for full erection to occur. ED may occur when there is an impairment or derangement to any of these systems. ED has been defined as the inability of a man to achieve or maintain an erection sufficient for satisfactory penetrative sexual intercourse 1 .
Post-RP ED may be neurogenic, venogenic, arteriogenic or a combination of these etiologies. In all cases, injury of the cavernous nerves occurs during dissection of the prostate. The injury, whether caused by contact, traction, electro-cautery or transection, initiates a cascade of events that culminates in ED. Microscopically, cavernous nerve-fiber injury initiates Wallerian degeneration that will incapacitate the axon back to the cell body, typically at the level of the spinal cord. The lack of nervous input at the end-organ (cavernous muscle) is a major contributor to cavernosal tissue degeneration and atrophy 2,3 . Venous leakage is another underlying mechanism responsible for ED after prostatectomy. Bilateral cavernosal nerve injury has been shown to induce cavernosal smooth muscle death which will lead to veno-occlusive dysfunction 3 . Chronic hypoxia, denervation, and activation of the TGF-β cascade are believed to initiate the apoptosis process, and increase the deposition of collagen-laden scar tissue 4-7 .
The initiating factor in the development of arteriogenic ED as a result of radical pelvic surgery is transection of the accessory pudendal arteries. These arteries arise from the peri-prostatic vasculature and course toward the penis and providing a significant portion of the arterial inflow required for normal erectile function 8,9 .
The incidence of post-prostatectomy ED has been reported to be between 29-88% 10-16 . This wide range of values can largely be attributed to failure to control various confounding factors including age, degree of nerve sparing, different definition of potency and preoperative ED. The CaPSURE study revealed that only 20% of patients returned to their preoperative baseline potency levels 1 year after RP 12 . In the Prostate Cancer Outcome Study (PCOS), 59.9% of men self-reported having ED following RP 14 . Similar results were found by the Memorial Sloan-Kettering Cancer Center group 17-19 . According to The Scandinavian Prostate Cancer Group, men who chose watchful waiting had a 45% incidence of ED. Those that selected RP as a treatment option experienced an incidence of ED at 80% 20 .

Inflatable penile prosthesis (IPP) utilization after RP
Phosphodiesterase-5 inhibitors (PDE5Is) initially were the first-line treatment for ED secondary to RP. However, they are not uniformly effective. In a subset of patients who initially respond, the response deteriorates over time as progressive cavernosal tissue damage occurs and subsequent venous leak develops 18,21,22 . Penile implant surgery is a viable treatment option in patients in whom nonsurgical ED treatments are unsatisfactory or are associated with adverse effects 23 . The utilization rate of penile implants after RP varies from 0.8 to 1.9% 24,25 . These reported rates have been obtained from analysis of the Surveillance Epidemiology and End Results (SEER) cancer registry database. The higher rate of 1.9% in a study by Stephenson et al. 25 is probably due to a younger cohort, as 45% of subjects were younger than 65 years. There are numerous reasons that could be postulated for low utilization of penile implants. Firstly, prostate cancer treatment modalities have improved, thereby decreasing the incidence of ED that is unresponsive to nonsurgical intervention. Secondly, effective nonsurgical treatment modalities have been developed as alternatives to surgical treatment, predominantly PDE5Is. Meta-analysis of contemporary publications by Tal et al. revealed an overall erectile function recovery rate of 58% among men younger than 60 years after RP 26 . The study acknowledged that the definitions of ED were different in each member study and some men used of PDE5i's for erectile rigidity 26 . Nevertheless, Stanley et al. found that there was no significant change in total number of penile implant procedures over a 10-year period before and after the introduction of sildenafil citrate 27 .

Surgical considerations
Cylinder placement Technique of dilation of fibrotic corpora. Corporal crossover and urethral perforation are more likely to occur during dilation of fibrotic corpora 28 . After placing the stretched penis into anatomical position (urethral meatus pointing in a superior direction), a small dilating instrument is placed into the corporotomy and slowly advanced in a latero-superior direction until it reaches the mid-glans penis. Sequential dilation is needed until the cavernosa accepts a 11-12 Fr. dilator. The most important caveat to remember is to orient the dilating instrument in a latero-superior direction when advancing the dilator within the corporal space 28 . This will prevent corporal crossover, as well as, provide a visual representation of the location of the dilator within the corpora. Tools used for dilation may include Metzenbaum scissors, Hagar dilators, Brooks dilators, Rossello cavernotomes, Mooreville cavernotomes, and the dialmezinsert dilator 29 .
Technique of corporal measurement. After corporotomy, PDS 2-0 stay sutures of are placed at the corporotomy edge. The sutures are used for traction, as well as, for closure of the corporotomy after insertion of the prosthesis. Historically, corporal dilation would then ensue with Brooks or Hegar dilators. After ensuring the corporal space was dilated to 14 mm, the corporal length was then measured and the prosthesis placed. In the contemporary setting, many implanters first measure the length of the corpora with the Furlow 30 . This narrow device provides enough passive dilation to place an inflatable prosthesis, especially if the corpora are non-fibrotic. If the corpora are fibrotic, the implanter would then dilate the corpora to ensure smooth insertion of the prosthesis 31 . When dilating or measuring the corpora, it is imperative to direct any instrumentation laterally to avoid urethral injury or corporal crossover 32 .
To measure the length of the corpora, gently advance the cylindrical measuring device proximally within the corporal space. When the bottom of the corpora cavernosa is reached, a measurement is recorded. Next, the penis is placed and securely held in "anatomical" position. The measuring instrument is passed distally towards the glans penis while angling the instrument laterally. A distal measurement is recorded and added to the proximal measurement. There should be no more than a 1-cm discrepancy between the right and left corpora. A >1 cm difference suggests incomplete dilation, corporal crossover, crural perforation or urethral perforation.
Prevention and management of corporal crossover Both proximal and distal corporal crossover can happen during dilation, measurement, or cylinder placement 33 . In addition, the initial correct distal tunneling technique using laterally directed dilators will help avoid crossover 28 . Side-by-side placement of the Brooks or Hagar dilators in each corpus to check for symmetry and proper positioning is the best way to check for proximal or distal crossover 34 . If a crossover is detected, the dilator may simply be redirected with the contralateral dilator left in place to prevent repeat crossover 28 .

Prevention and management of perforation
Proximal crural perforation is suspected when there is asymmetry of proximally positioned dilators or a significant length differential. Gentle dilation and corporal measurement can prevent this manageable complication. In the event of proximal perforation, management may take the form of direct repair of perforation, creation and placement of windsock using an "off-the-shelf" implantable graft, creation of a hammock using a rear-tip-extender, or anchoring of cylinder tubing to tunica 35,36 . A simple 'U-type' suture will prevent proximal cylinder migration.
Distal corporal and urethral perforation requires termination of the procedure, especially if distal perforation occurs during dilation of the first side 37 . If a second side is perforated after successful cylinder placement of the contralateral side, the single cylinder may be left on the non-perforated side 38 . Urethral tear may be repaired or, if very small, left to heal over the catheter 39 . Many surgeons will abandon the case during urethral injury in fear of prosthesis infection.

Reservoir placement
The reservoir is normally placed in space of Retzius. This is done to reduce the creation of inguinal floor weakness and to reduce the potential risk of visceral injury. After ensuring complete bladder drainage, the index finger is placed through the IPP incision and advanced to the medial aspect of the external inguinal ring. Using firm pressure, the finger is advanced in a posterior direction, piercing transversalis fascia. If finger pressure is inadequate, the fascia can be perforated with the tip of an instrument (scissors or clamp). This action will create a rent large enough to insinuate an index finger into the space of Retzius. Alternatively, a long-bladed nasal speculum is useful in expanding the retroperitoneal space.
If the space of Retzius is obliterated due to previous pelvic surgery, ectopic placement of the reservoir should be considered 40,41 . The reservoir may be placed in the deep to the abdominal musculature superior or posterior to transversalis fascia 42 . A Foerster or Debakey clamp may be used to advance the deflated reservoir to its ectopic position. Stember et al reported the outcomes of 2687 men who underwent ectopic reservoir placement 42 . In total, 83%, of men had reservoirs placed posterior to the transversalis fascia. The remainder had reservoirs placed in the anterior transversalis space. No injuries to the bowel or major blood vessels occurred with initial insertion of the reservoir, however two patients experienced bladder injury. Eight patients required reservoir revision secondary to herniation 42 .

Prevention and management of bladder and bowel perforation
The most serious intraoperative complications of penile prosthesis insertion occur during reservoir placement 43 . Traditionally, the reservoir is placed blindly in a retrograde fashion into the space of Retzius through a penoscrotal incision. The serious potential complications include vascular injury, bowel perforation and bladder perforation 44 . Vascular injury (arterial or venous avulsion) may occur during overly aggressive finger or instrument dilation of the inguinal ring. In the event of brisk bleeding, tapenade with an index finger or sponge stick is advised 45 . Direct access into the space of Retzius is then accomplished through an inguinal incision. Meticulous inspection of the pelvic sidewall will frequently localize the avulsed venous vessel. In the event of vascular injury of the major pelvic vessels, consultation from a vascular surgeon is recommended.
Bladder injury is a complication that should be recognized and managed immediately. Prior pelvic surgery or radiation may result in adherence or fixation to the pelvic sidewall. Bladder perforation can happen while piercing the transversalis fascia 46 . Emptying the bladder prior to placing the reservoir can decrease the incidence of these injuries. Bladder injury is noted when gross blood is seen in the urine or the observation of urine emanating through the IPP incision 31 . The injury can be confirmed via flexible cystoscopy or by an on-table cystogram. In case of bladder injury due to scissors, the reservoir should be removed and placed on the contralateral side. The bladder should be drained for 7-10 days. Cystogram should be done prior to catheter removal.
The bowel may be damaged in a similar mechanism to bladder injury during reservoir placement 31 . Upon recognition bowel injury (succus entericus in the wound), a general surgeon should be consulted for repair and the prosthesis removed.

Satisfaction rates after penile prosthesis implantation
Serial reports regarding of penile prosthesis surgery outcomes demonstrate excellent long-term mechanical reliability of contemporary prosthesis models; satisfaction is superior when compared to PDE5Is and injections. Carson et al. performed a retrospective long-term multicenter study on 372 patients who underwent penile prosthesis implant and focused on the longevity, morbidity and patient satisfaction 47 . More than 80% of patients were satisfied with the function of the device, the ease of inflation, and level of rigidity. Steege et al. reported that patient satisfaction with semi-rigid prostheses was higher than 90%, however, inflatable devices enjoy a slightly higher satisfaction 48 . Holloway and Farah reported that the AMS 700 Ultrex prosthesis had a 86% patient and 76% partner satisfaction at a mean postoperative follow-up of 42 months 49 . In a study by Rajpurkar et al., the investigators demonstrated significantly enhanced erectile function and sexual satisfaction when compared to those receiving sildenafil and intracavernosal prostaglandin 50 .
The psychosexual adaptation to penile implant may take up to 6 months. The patients experience a marked enhancement in erectile function with elevation of libido. Apprehension regarding the maintenance of an erection during intercourse is markedly assuaged. In addition to an upsurge in the regularity of sexual activity, a decrease in feeling of sadness, depression, anxiety and an improvement in sexual satisfaction has also been noted 51 .
Two major factors contributing to high level of satisfaction are rapid generation of erection and consistently excellent rigidity. Other factors, such as degree of postoperative pain and swelling, postoperative complications, ease of concealment, cosmetic outcome, device function, ease of use and partner acceptance, are critical in determining the patient satisfaction. Potential predictors of patient dissatisfaction with penile prosthesis include Peyronie's disease, a body mass index >30, or previous RP 52 .

Predictors of requiring a penile prosthesis
The natural recovery time of erectile function may be up to 24 months after radical pelvic surgery; however, resultant penile rigidity may be maximized by early treatment with intracorporal injection therapy 53-55 . Various different symptomatic treatments are available for patients who fail to regain a natural erection. Sildenafil becomes effective in the late recovery phase as the nerves recover from intraoperative injury 54 . At 2 or more years from surgery, the recovery of natural function and improved response from other therapies is unlikely and implantation of penile prosthesis is warranted 54 . A study by Tal et al. found that men who had surgery as an initial treatment (versus radiotherapy), were of a younger age, were of African/American/Hispanic race, were unmarried, and were living in a geographic region other than the North-east were more likely to utilize penile implants 25 . Similarly, in a retrospective analysis of claims data from Medicare & Commercial databases of 3928 men undergoing penile prosthesis, Segal and Burnett elucidated the factors with the greatest predictive strength of penile prosthesis implantation, which included a diagnosis of prostate cancer, a diagnosis of diabetes mellitus and previous treatment with first-line ED therapy 56 .

Conclusion
In the population of patients with prostate cancer, the concept of survivorship has become a central tenet of patient care. To that end, quality of sexual life, and especially erectile function has become a significant issue. Penile prosthesis surgery remains an excellent option for restoring erectile function to those who fail more conservative measures. IPP implantation enjoys high satisfaction rates for patients and their partners. Intraoperative complications can be distressing, but with prompt recognition, most of these complications can be navigated with excellent postoperative results.

Data availability
No data are associated with this article.

Competing interests
No competing interests were disclosed.

Grant information
The author(s) declared that no grants were involved in supporting this work. questionnaire on impotence, incontinence and stricture after radical