John J. Bauer, M.D.
Pitfalls of Penile Implants
John J. Bauer, MD, Urologist
Avoiding Sensory Loss
The preferred surgical approach for penile prosthesis implantation is the transverse upper scrotal approach, a variant of the penoscrotal approach. One of its most important advantages is that it avoids possible damage to the dorsal nerves of the penis. Other advantages include easier and more complete corporeal exposure and the ability to anchor the pump of the prosthesis in the scrotum.
Ultrex Cylinder Deformities
The ultrex cylinder, while a landmark in penile prosthesis technology due to its ability to increase penile length with device inflation, also introduced a new problem: the S-shaped cylinder deformity. This is the result of a small sizing error that occurs when the surgeon implants a cylinder that is a little too long for the corpus cavernosum. To avoid this problem, the surgeon should use a measuring technique that results in a cylinder that fills the corpus cavernosum but does not buckle or bulge out of the corporotomy. The surgeon should inflate the cylinders completely with saline so they are rounded before corporotomy closure. This is necessary because otherwise it is impossible to accurately assess cylinder sizing. After the cylinders are fully inflated, they must lie absolutely flat within the corpus cavernosum.
When to Select a CX Versus an Ultrex Cylinder
The middle layer of the CX cylinder allows controlled girth expansion whereas the middle layer of the Ultrex cylinder allows both controlled girth and length expansion. The surgeon should choose a CX cylinder when
Fluid Volume Problems
Since silicone is semipermeable, the filling solutions for hydraulic prostheses must be isotonic. Prefilled and preconnected devices contain normal saline. Normal saline should be used for filling the components of a penile prosthesis. When contrast as the filling medium is desired, as for an artificial sphincter, dilutions of the contrast with sterile water must be made according to manufacturer's instructions.
Palpable Input Tubing
To avoid having tubing that is palpable or even visible at the base of the penis, a distal corporotomy can be made and the input tubing routed through a more proximal stab incision. Another option is to make the corporotomy more proximal and have the input tubing exit directly through the most proximal aspect.
With use of the penoscrotal approach or a modification, a Darto's pouch can be created to hold the pump or pump tubing. Creation of a Darto's pouch has these advantages:
Auto inflation of three-piece inflatable prostheses is a common complaint although sometimes what the patient views as auto inflation actually is not. It will occur if the abdominal fluid reservoir pressure is high. Also, during healing, the cylinders should be kept deflated so that the fibrous pseudo-capsule that forms around the reservoir will not prevent eventual full deflation.
Avoiding Ventral Chordee
During the healing phase, an implant recipient should wear his penis up on the lower abdomen pointed toward the umbilicus. This is a necessary precaution since the body reacts to silicone by forming a fibrous pseudo-capsule around it and if an implant recipient wears the penis down during healing a permanent ventral chordee may result.
To avoid urethral injury during corporeal preparation, distal dilation should begin with an 8 millimeter Hegar dilator. During distal dilation the tip of the dilator should be kept under the dorsolateral surface of the tunica albuginea with the dilator directed away from both the urethra and the septum. If there is fibrosis and the dilator will not pass without undue force, Metzenbaum scissors should be substituted for the dilator. If this substitution does not succeed, the corporotomy should be extended. However, if urethral perforation occurs, the implant procedure should be terminated. In the case of crural perforation, it is usually possible to use a larger dilator and direct it past the perforation.
Infection is a significant complication in this type of surgery since it results in the removal of the prosthesis. Since bacteria adhere to silicone and all the parts of a prosthesis are connected, the entire device must be removed including the rear tip extenders. Options following infection include
Penile prosthesis implantation may be quite difficult when the penis is fibrotic. There are two types of penile scarring: fibrosis of the tunica albuginea (plaque formation) and intracorporeal (cavernosal) fibrosis.
Tunica Albuginea Fibrosis
This type of fibrosis is usually the result of Peyronie's disease, or it may occur after a rupture of the tunica albuginea. Intracavernosal pharmacotherapy may also cause tunica albuginea fibrosis.
Since the intracorporeal smooth muscle is usually normal, implanting a prosthesis in patients with tunica albuginea fibrosis is often accomplished without difficulty. If a malleable or positionable DuraPhase prosthesis is used, penile curvature can be corrected at the end of the implant procedure by bending or molding the penis. If the degree of penile curvature is significant a straightening procedure or corporoplasty should be done.
Corporoplasty is usually performed through a penile degloving approach. (Permission to circumcise should be obtained from an uncircumcised patient to avoid a buried suture line under the prepuce.) The degloving incision is carried down through the Dartos fascia, and the penile skin, subcutaneous tissues, and Dartos fascia are reflected to the base of the penis. To correct a dorsal chordee, the neurovascular bundle is elevated by making parallel incisions through Buck's fascia at the 2 and 10 o'clock positions and then Cavernosal Fibrosis dissecting under the bundle. Afterwards, the prosthesis is inflated and the point of maximal curvature is noted. Using electrocautery, the surgeon makes a transverse incision under the neurovascular bundle and continues it down to the penile cylinders. (The silicone cylinders of the AMS 700CX or the AMX Ultrex devices will not be damaged by electrocautery. However, it cannot be used with the Mentor inflatable prosthesis because it will damage the polyurethane Bioflex cylinders.) When the cylinders are exposed and the septal tissue between the cylinders is divided, the transverse corporotomy gapes open causing a partial or full correction of the chordee. Usually one appropriately placed incision is enough to close but occasionally two are required.
Defects created by these incisions can be covered with polytetrafluoroethylene (PTFE), dacron, dermal, Buck's fascia, or tunica vaginalis patches. Dacron or PTFE patches require the use of nonabsorbable suture, whereas tissue patches can be sewn in with absorbable suture. Bleeding from these incisions can be controlled by partially inflating the cylinders for 48 hours.
To correct a ventral chordee, the corpus spongiosum and urethra must be separated from the ventral surface of the corpora cavernosa. Electrocautery is used to make a transverse incision at the point of maximal curvature and then down to the cylinders releasing the chordee. If necessary, defect closure with patches can be performed.
CX (rather than Ultrex) cylinders should be chosen for inflatable penile prosthesis implants in men with penile curvature. Because of their girth-only expansion, CX cylinders have better straightening properties. After the cylinders are implanted and while the patient is still under anesthesia, the prosthesis should be inflated until the penis begins to curve. The surgeon should then grasp the penis with both hands and forcibly straighten it. (Sometimes a cracking noise is heard as a Peyronie's plaque is ruptured.) Afterward, continue to inflate the prosthesis and manually straighten the penis until the prosthesis is fully inflated and the penis is reasonably straight.
Cavernosal fibrosis occurs after removal of an infected implant, after priapism, or it may be idiopathic. This type of fibrosis may also be caused by intracavernous pharmacotherapy.
When a corporotomy is made, normal corporeal tissue has a characteristic appearance. The tunica albuginea has a thickness of about 2 millimeters and there is an abrupt transition between it and the underlying erectile tissue which is brownish-red and appears mesh-like. When severe cavernosal fibrosis exists, however, the transition between the under surface of the tunica albuginea and the erectile tissue is not obvious. In addition, the fibrotic erectile tissue is pale yellow, the mesh-like appearance has been lost, and bleeding is reduced.
Implanting a prosthesis in a patient with cavernosal fibrosis can be quite difficult. The preferred surgical approach is a transverse scrotal incision just below the penoscrotal junction which places the initial corporotomy at the midpoint of the corpus cavernosum. This enables maximal control during both distal and proximal dilation. Furthermore, this approach provides access to nearly the entire corpus cavernosum. It also avoids possible damage to the dorsal nerves of the penis and makes it easier to anchor the pump in its sub-Dartos pouch.
Initially, 2 cm corporotomies are made and these are typically adequate for corporeal dilation and cylinder implantation. However if an 8 millimeter Hegar dilator cannot be easily introduced proximally and distally for the entire length of the corpus cavernosum, it suggests that some fibrosis exists. If the dilator is forced, urethral injury or perforation of the tunica albuginea may occur. To avoid this, Metzenbaum scissors should be used in place of the dilator. The tips are spread slightly as the scissors are advanced to both the proximal and distal ends of the corpora cavernosa. As the scissors are withdrawn, the tips are spread approximately 2 cm. Progressive dilation with Hegar dilators starting with an 8 millimeter dilator is usually possible then. Alternatively, a Dilamezinsert instrument (Lone Star Medical Products, Inc., Houston) or Rossello-Carrion dilators may be used.
When severe fibrosis exists, use of the Metzenbaum scissors followed by the Hegar dilators will not be successful. Through a transverse upper scrotal incision, proximal exposure of the entire crus can be gained by retraction of the scrotal contents. The distal corpora can also be entirely exposed through a ventral midline penile incision that joins the transverse scrotal incision at its midpoint. After each corpus cavernosum has been exposed for its entire length, the initial 2 centimeter corporotomy is extended proximally and distally. Then a prosthesis cylinder or a non-hydraulic prosthesis can be laid into the bivalved corpus cavernosum. Because closure of the tunica albuginea over the prosthesis is usually not possible, a patch of PTFE or Dacron is sutured in place with 3-0 prolene.
Sometimes an alternative method for implanting prostheses in these patients is possible. After extending the corporotomy and placing multiple stay sutures through the cut edges of the tunica albuginea, a plane is established between the under surface of the tunica albuginea and the fibrotic cavernosal tissue by sharp dissection with Metzenbaum scissors. By extending this plane, a core of fibrotic tissue can often be removed. If so, it is usually possible to achieve primary closure of the tunica albuginea following implantation of the prosthesis.
The AMS 700CXM is a smaller, 3-piece, inflatable, penile prosthesis which was originally developed for Asians. The CMX cylinders provide girth expansion only and have a deflated diameter of 9.5 millimeters and an inflated diameter of 14.2 millimeters.
This prosthesis will often fit in fibrotic corpora when no other device will and there is less risk of erosion with it than with a rod prosthesis. For these reasons, the AMS 700CXM is the prosthesis of choice for reconstructive surgery.
Explant/Implant vs. Revision
Early penile prosthesis implant revisions were usually due to mechanical failures and occurred relatively soon after the implant. During the revision surgery, the surgeon would determine which part of the prosthesis had failed and then would replace only that part.
Today mechanical failures are few and when revision surgery is required the current trend is to replace the entire device.