Rationale For Interposition Sural Nerve Graft

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Given our current knowledge of the anatomy, function and regenerative ability of the pelvic autonomic nerves, it is not unreasonable to think that one could improve the functional outcome for patients with locally advanced prostate cancer who have undergone either unilateral or bilateral wide resection of the neurovascular bundle(s) (leaving the nerve intact on the prostatectomy specimen) by interposing a nerve graft to the free ends of the resected cavernous nerve(s). In patients with pathologic stage T3 disease, this approach would have the potential to improve cancer control by reducing the incidence of positive surgical margins as compared with nerve-sparing surgery and to reduce the incidence of impotence, and possibly incontinence, as compared with non-nerve-sparing surgery without nerve graft. Four key conditions determine whether patients can benefit from this approach. First, cavernous nerve function must be restored on the grafted side once the neuro-regenerative process is complete. Second, since most NVB resections are unilateral, patients who undergo unilateral NVB resection must have reduced potency and/or continence compared to patients that undergo bilateral nerve-sparing surgery. Third, the surgeon must be able to predict the presence and location of extracapsular extension (ECE) of the carcinoma in order to avoid inappropriately resecting potentially salvageable NVBs. Finally, wide resection of the NVB must improve cancer control in the presence of ECE along the resected NVB.

The ability of the cavernous nerve to regenerate after complete transection was demonstrated in rodents as early as 1992. In these studies, cavernous nerve function was restored by interposition nerve grafting with the genitofemoral nerve to repair defects created in the cavernous nerve by excision of short segments.22,23 Walsh was the first to perform interposition nerve grafting of excised cavernous nerves in humans at the time of RRP. He used a genitofemoral nerve segment for interposition grafting. However, he did not see a clear benefit and the procedure was abandoned.24 Conclusive evidence that the human cavernous nerves could regenerate after wide local excision with interposition graft repair was first reported by an interdisciplinary group from Baylor College of Medicine, led by Peter Scardino.25 The first autologous unilateral interposition nerve graft using the sural nerve was performed in January 1997. The first bilateral nerve graft was performed in March of 1997. As far as we know, these were the first successful efforts, in humans, to restore erectile function after bilateral cavernous nerve resection with repair by interposition nerve grafting at the time of RRP. Analysis of erectile function in the first 12 patients with at least 12 months of follow-up after bilateral nerve grafts revealed that four had spontaneous erections sufficient for unassisted intercourse, three had no spontaneous erections and the remaining five had partial erections.26 Of the five men with partial erections, two reported erections sufficient for intercourse with sildenafil (Viagra) treatment. None of the patients in a control group of men who had undergone bilateral nerve resection without nerve graft had erections. A multidisciplinary team involving specialists in erectile dysfunction, prostate cancer surgery and microsurgical nerve reconstruction contributed to the development of this novel technique. The sural nerve was selected for interposition grafting because it has a larger caliber than the genitofemoral nerve. The smaller caliber of the genitofemoral nerve may have explained the failure of earlier attempts at cavernous nerve reconstruction.

Unilateral NVB resection significantly decreases postoperative potency, especially in men older than 50. High-volume academic centers have reported decreases in potency rates of about 50% in patients who undergo unilateral NVB resection.27-30 Nevertheless, a distinction should be made between 'non-nerve-sparing' surgery and purposeful, wide resection of the NVB. For example, it has been reported that potency rates after radical prostatectomy performed in a community setting fall within a very narrow range, irrespective of the reported degree of nerve-sparing performed as part of the surgery. Of men who had unilateral or bilateral nerve-sparing surgery in one study, 41% and 44%, respectively, were potent. Surprisingly, 33% of men who had bilateral non-nerve-sparing procedures were also potent.31 Given the experience at most academic centers, it is unlikely that patients who were included in this study as undergoing non-nerve-sparing surgery underwent wide resection of the NVB. In our experience, unilateral, intentional wide resection of one NVB decreases postoperative potency. Few, if any, patients that undergo intentional wide resection of both NVB are potent postoperatively.

Tumor involvement of the NVB cannot yet be predicted with 100% certainty. Nevertheless, the presence of ECE can be predicted relatively accurately by integrating a number of parameters including the prostate specific antigen (PSA), the % free PSA, results of the digital rectal examination (DRE), transrectal ultrasound findings, and the extent and Gleason score of the cancer in the biopsy specimens. Currently, at our institution, in patients for whom the decision to perform nerve-sparing RRP appears equivocal, a 12-core biopsy is performed, including six sextant-directed cores, and six laterally directed cores at the base, mid and apical prostate, if one has not already been obtained at diagnosis. We have recently shown that this 12-core extended, regional, transrectal ultrasound-guided

Sural Nerve Interposition Graft During Radical Prostatectomy

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