Histological study of the cavernous nerve mesh outside the periprostatic region: anatomical basis for erectile function after nonnerve sparing radical prostatectomy.

We identified the cavernous nerve mesh that exists caudal or posterior to the periprostatic region between the bilateral slings of the levator ani. We also assessed whether nonnerve sparing radical prostatectomy could be modified. Using histological sections from 24 elderly cadavers we investigated nerve anatomy by immunohistochemistry for S100 protein, neuronal nitric oxide synthase, vasoactive intestinal polypeptide and tyrosine hydroxylase. The cavernous nerve mesh formed a U-shaped column attached to the lateral and posterior aspects of the rhabdosphincter. It was greater than 10 mm thick along the anteroposterior axis and 5 to 10 mm wide from the lateral margin of the rhabdosphincter. Composite neuronal nitric oxide synthase positive nerves ran obliquely with a highly tortuous course. The anterior margin of the nerve mesh corresponded to the anterior margin of the rhabdosphincter. Nerve mesh left-right communication was seen at and near the anterior margin. Bilateral periprostatic nerves joined posterior to the urethra and immediately anterior to the rectourethralis muscle, forming a midsagittal nerve mesh corresponding to the base of the U. The periprostatic nerves also formed a mesh or bundle but it was much thinner and smaller than the U-shaped mesh along the rhabdosphincter. Neuronal nitric oxide synthase positive nerves consistently contained tyrosine hydroxylase positive sympathetic nerve fibers but there were few vasoactive intestinal polypeptide positive fibers. The pudendal nerve and its branches were negative for neuronal nitric oxide synthase. Bilateral resection of the neurovascular bundle does not remove all cavernous nerves because these nerves cover the rhabdosphincter and perirectum caudal to the level of the apex of the prostate.