Invited Discussion

In their paper, Muneuchi et al describe their experience with cavernous nerve reconstruction after radical prostatectomy in 22 patients. Fifteen of these patients had more than 1 year of follow-up and were available for functional outcome analysis. Of the 10 patients who had unilateral nerve reconstruction, erectile function was noted in six of them, and potency was recovered in four (40 percent potency rate). In five patients with bilateral cavernous nerve reconstruction, two patients were able to regain erectile function; however, none was able to regain potency.

The authors discuss two particular difficulties in performing cavernous nerve reconstruction: 1) harvesting the sural nerve graft with the patient in thesupine position; and 2) placing the nerve grafts deep within the pelvis with poor visibility and using inadequate instruments. The authors' mean time for nerve harvesting and reconstruction was 1 hr 50 min for unilateral reconstruction and 2 hr 40 min for bilateral reconstruction.

Our initial experience with cavernous nerve reconstruction came in a prospective study of 30 men that was designed to evaluate the efficacy of bilateral cavernous nerve reconstruction. At a mean follow-up of 23 months, 18 patients (60 percent) could attain spontaneous erectile activity, and 13 of them (43 percent) had regained potency.[1] Early on, my colleagues and I experienced the same difficulties as Muneuchi et al.: we also found that harvesting the sural nerve with patients in the supine position while the prostatectomy was being performed was very cumbersome and difficult. In addition, lifting the leg and moving it, as required to harvest the sural nerve graft, interfered with the prostatectomy.

My colleagues and I quickly realized that we needed to devise a better method for harvesting the nerve graft, and have since found that the best approach for us is to first harvest the sural nerve graft with the patient in a lateral position.[2] The nerve is harvested by placing a tourniquet on the thigh and making two small incisions at the proximal and mid-calf, along the course of the sural nerve; each incision is approximately 3 cm long. Through these incisions, approximately 15 cm of nerve can be harvested for grafting, which is more than adequate, even for bilateral cavernous nerve reconstruction, because each nerve defect is approximately only 5 cm (Fig. [1]). The entire procedure takes 10 to 15 min, including dressing the wound and repositioning the patient. Using this technique, we are able to quickly harvest the sural nerve graft, and then allow the urologist to proceed with the radical prostatectomy, without either procedure getting in the way of the other.

Figure 1 Harvesting of sural nerve graft.

The second difficulty that the authors mentioned is the technical problem of placing the nerve graft. To improve the visualization, I wear a headlight for better lighting within the deep pelvic area. As the authors pointed out, the instruments available were just inadequate for doing a fine nerve reconstruction in the deep pelvis. Therefore, I designed and developed my own set of instruments with the help of Micrins Surgical (Lake Forest, IL USA), including a needle holder, forceps, and dissecting scissors, that are specific for this procedure (Fig. [2]). They are commercially available. (I do not have any financial interest.) These instruments have made performing the procedure much easier than in the past. I generally place two epineurial sutures for nerve repair and use 7-0 polypropylene sutures. Because the sural nerve graft that I harvest does not have any branches, it does not matter which end is placed proximally or distally. I perform the distal anastomosis first because it is the more difficult and requires more retraction, and then I do the proximal anastomosis. There is a steep learning curve in placing these nerve grafts, and initially the procedure took a long time, but now it takes 15 to 20 min per side. Thus, for unilateral cavernous nerve reconstruction, including the nerve harvesting and the reconstruction, a total of 20 to 30 min is required, and for bilateral cavernous nerve reconstruction, 40 to 50 min.

Figure 2 Three different generations of cavernous nerve reconstruction instruments. Three on the far right are the newest generation.

From December 1998 through December 2004, we performed approximately 270 cavernous nerve reconstructions following radical prostatectomy; 110 were bilateral and 160 were unilateral. We are currently reevaluating our results in the cases of bilateral cavernous nerve reconstruction; however, our preliminary results show that the erectile activity remains in the 50 to 60 percent range, with a potency rate of 25 to 30 percent, which is less than the 43 percent potency that was originally reported in our earlier prospective study. This finding is not really surprising because patient selection is now not as strict as it was during the original study, and postoperative erectile dysfunction therapy, which was mandatory during our study, is now encouraged but not strictly enforced. Postoperative erectile dysfunction therapy is initiated 6 weeks postoperatively; patients are given sildenafil 25 mg every other day and asked to obtain a full erection at least three times a week using either a vacuum pump or an intracavernous injection of Trimix (prostaglandin E, phentolamine, papaverine) solution. We believe that this therapy does facilitate a patient's ability to regain potency. For unilateral cases, the potency at 1-year follow-up appears to be 40 to 50 percent, but we are currently conducting a prospective, randomized study to more accurately determine the efficacy of unilateral cavernous nerve reconstruction.

With the increased use of a laparoscopic approach to prostatectomy, cavernous nerve reconstructions using conventional and robot-assisted laparoscopy have been performed and will most likely continue to increase in frequency.[3] [4]

I applaud Muneuchi et al. for performing cavernous nerve reconstructions following radical prostatectomy despite the technical difficulties and challenges. It appears that they are going through the same growing pains that my colleagues and I went through during our early experience.

In summary, on the basis of our experience, I believe that harvesting the nerve graft first with the patient in the lateral position makes harvesting the nerve graft rather easy, while adding very little time to the entire procedure; in fact, this approach might ultimately be much quicker than trying to harvest the nerve graft simultaneously during the prostatectomy with the patient in the supine position. The new instruments also make performing the nerve graft procedure much easier. Finally, the postoperative erectile dysfunction therapy may improve the potency rate in patients who have undergone cavernous nerve reconstruction.

REFERENCES

• 1 Chang D W, Wood C G, Kroll S S, Youssef A, Babaian R J. Cavernous nerve reconstruction to preserve erectile function following non-nerve sparing radical retropubic prostatectomy: a prospective phase I study.  Plast Reconstr Surg. 2003;  111 1174-1181
• 2 Chang D W. Minimal incision technique for sural nerve graft harvest: experience with 61 patients.  J Reconstr Microsurg. 2002;  18 671-675
• 3 Turk I A, Deger S, Morgan W R, Davis J W, Schellhammer P F, Loening S A. Sural nerve graft during laparoscopic radical prostatectomy. Initial experience.  Urol Oncol . 2002;  7 191-194
• 4 Kaouk J H, Desai M M, Abreu S C, Papay F, Gill I S. Robotic assisted laparoscopic sural nerve grafting during radical prostatectomy: initial experience.  J Urol . 2003;  170 909-912