Penile Prosthesis Implantation Workup

• The workup of erectile dysfunction (ED) is controversial and not standardized among urologists. Some practitioners do not attempt to perform complex diagnostic procedures to determine the exact cause of the ED, reasoning that all organic impotence is treated in the same manner and that a specific diagnosis is not more helpful to the patient. Others, usually specialists in impotence, have a multitiered approach to the diagnosis of ED.
• Endocrine disturbances are an important and potentially treatable cause of ED. The hypothalamic-pituitary-testicular axis is a very important and finely balanced force that helps regulate many bodily functions, including sexual drive and behavior. The hypothalamus secrets gonadotropin-releasing hormone that stimulates pituitary production of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). These in turn stimulate testicular function, including production of androgens such as testosterone and dihydrotestosterone. Both of these hormones are important for male genital fetal development, formation of male secondary sexual characteristics, and libido.
• In developed adult men, testosterone greatly influences sexual behavior because (1) castrated men report decrease in sexual interest and performance, (2) hypogonadal men can have increased libido if supplemented with exogenous androgens, and (3) antiandrogens, such as those administered to treat prostate cancer, can greatly suppress sexual desire and performance in men.
• The complete workup of ED should include a biochemical/hormonal profile to help delineate underlying endocrinopathies such as hypogonadism or hyperprolactinemia, which may be able to be managed medically.
• Many clinicians investigate an initial testosterone level prior to sending a more exhaustive panel. Some specialists who focus on treating ED may elect to send a larger panel.
• More extensive laboratory tests may include prolactin, free testosterone, and gonadotropin (both FSH and LH) in addition to a screening testosterone.
• Of course, the first step to help a clinician investigate ED is a careful history and physical examination. In the physical examination, the clinician should be aware of secondary sexual characteristics, such as axillary and pubic hair distribution, as well as body habitus. In some instances, this provides clues about underlying endocrine problems.
• When low levels of gonadotropins and testosterone are present, the clinician should be suspicious of a hypothalamopituitary cause and consider cranial imaging, such as MRI, to rule out pituitary or hypothalamic tumors or the empty sella syndrome.
• Patients with thyroid problems experience sexual problems. Hyperthyroidism can cause decreased libido, most likely because of increased levels of circulating estrogens. Hypothyroidism can cause decreased testosterone levels and increased prolactin levels, causing erectile difficulties and decreased libido.
• Some controversy exists regarding penile prosthesis implantation in persons with diabetes. Early studies indicated a high infection rate in persons with poorly controlled diabetes with elevated hemoglobin A1c levels. Subsequent studies challenged this practice, but, as mentioned above, the practice is not uniform. Persons with poorly controlled diabetes have a higher complication rate due to infection, compliance issues, and tissue healing. Therefore, their satisfaction rates are lower than those of persons without diabetes.

Many practitioners do not feel that preoperative imaging studies are required before penile prosthesis implantation. However, others prefer a complete workup of the etiology of ED, which can include arteriography, penile duplex with Doppler flow, and cavernosography.

• Arteriography

  • This study rarely is performed, and practitioners sometimes pose the question, "Is it worth all the trouble?"
  • Penile arteriography proves to be extremely challenging because of the wide variation in penile arterial anatomy. Often, selective catheterization of the intended pudendal arteries is not only difficult but also extremely time consuming. Over time, the artery can spasm and produce a false reading, and, sometimes, accessory internal pudendal arteries can mislead the true extent of penile inflow.
  • The best arteriograms should be performed with cavernosal arterial distention to view the cavernosal arteries in their entirety and then follow the arteriolar flow.
  • The cavernosal arteries in the flaccid state are 0.2-1 mm in diameter, which can increase to 1-1.5 mm. In most instances, the spatial resolution, even with modern angiographic instruments, can account for a 30% error rate in vessel diameter. Operator inconsistency can further increase the error rate.
  • Many pragmatic experts question the value of arteriography, especially when considering what patients must undergo, its high cost, and the limited information it provides. Most experts do agree that its most useful application is in patients with pelvic trauma who are young and may have discrete lesions that are amenable to vascular intervention, such as to repair steal syndrome or simply to cannulize or bypass an area of obstruction or stenosis.
• Duplex sonography

  • Urologists specializing in ED often use the duplex sonography modality. It has some clear advantages over other diagnostic tests. It can be performed in an office setting and is noninvasive. Imaging is good, and Doppler blood flow studies can be accomplished on individual cavernous arteries. In addition to its ability to demonstrate the vascular state of penile vessels, it also can reveal a venous leak, high-flow priapism, and calcium deposits characteristic of Peyronie disease.
  • The study entails first obtaining baseline images and measurement on the flaccid penis; then, a pharmacologic agent is injected to induce erection. Cavernous arterial diameter and pulsatility are recorded, as well as any anomalous anatomy or findings. This information allows the urologist objective criteria concerning flow velocity and arterial caliber to gauge vascular health.
  • Some authors agree that a peak systolic velocity of greater than 35 cm/s indicates a normal arterial supply, and those with a velocity of less than 25 cm/s are considered to have severe arterial disease. More subjective is the pulsatility or ability to dilate regarding penile arteries. Most experts agree that, in general, a forceful pulsation with good change in arterial diameter between systolic and diastolic phases indicates normal arterial function and signals a healthy arterial system.
  • Proponents of duplex ultrasonography say that it is an effective modality to evaluate vasculogenic impotence. However, it also has problems that can affect accuracy; the procedure is performed in a nonsexual office setting, patients vary in their response to vasogenic agents in both dosage and time to erection, and the test is very operator-dependent.
• Cavernosography

  • This study uses radiocontrast solution injected into the corpora cavernosa during an artificial erection. The injection is a percutaneous intracorporal infusion of fluid via a needle or catheter. It should always be performed after a vasoactive agent is injected in an attempt to induce erection.
  • By performing this study, clinicians hope to visualize areas of venous leak, where blood normally trapped during erections leaks out so that arterial inflow cannot maintain adequate erections.
  • Areas of leak include the glans, corpus spongiosum, superficial and deep veins, cavernous veins, and areas of Peyronie plaque. The original thought was that if these areas could be ligated surgically, erectile function could begin to favor arterial inflow. However, enthusiasm for cavernosography and venous ligation has waned because of poor long-term results.

• Nocturnal penile tumescence testing

  • The NPT test takes advantage of the natural sleep-related erections found in potent men during rapid eye movement (REM) sleep. The primary goal of NPT testing is to distinguish organic etiology from psychogenic causes of ED.
  • NPT testing was once associated with a wide assortment of tests, including those for sleep study, such as electroencephalography, electro-oculography, electromyography, and video monitoring. Today, many urologists use an abbreviated portable home model (RigiScan), which a patient can take home after he is instructed on its proper use. Essentially, it entails applying a measuring device to the penis that measures the number of nocturnal erections, axial rigidity at base and tip, duration of erection, and level of maximal rigidity.
  • NPT testing and the introduction of the portable RigiScan for home use in 1985 still have some controversies, particularly regarding the lack of standardized parameters and limited clinical trials.
  • Cilurzo et al (1992) suggest the following for normal NPT parameters:^[7]
    • Achieving 4-5 erectile episodes per night
    • Mean duration of erectile episodes greater than 30 minutes
    • Increase in circumference of greater than 3 cm at base and 2 cm at tip during erectile episodes
    • Greater than 70% maximal rigidity at both tip and base during erectile episodes
  • NPT testing, although expensive, can help differentiate organic from psychogenic impotence and thus prevent further unnecessary workup and possible unwarranted intervention.