RECONSTRUCTIVE UROLOGY

Identification of communicating branches among the dorsal perineal and cavernous nerves of the penis
Yucel S, Baskin LS
From the Department of Urology and Pediatrics, University of California-San Francisco, Children’s Medical Center, University of California-San Francisco, San Francisco, California
J Urol. 2003; 170:153-8

• Purpose: The mechanism of human erection requires the coordination of an intact neuronal system that includes the cavernous, perineal, and dorsal nerves of the penis. We defined the communication of these 3 nerves that travel under the pubic arch using specific neuronal immunohistochemical staining and 3-dimensional reconstruction imaging technique.
• Materials and Methods: A total of 18 normal human fetal penile specimens at 17.5 to 32 weeks of gestation were studied by immunohistochemical techniques. Serial sections were stained with antibodies raised against the neuronal markers S-100, and neuronal nitric oxide synthase (nNOS), vesicular acetylcholine transporter (VAChT), calcitonin gene-related peptide and substance P.
• Results: The continuation of the dorsal neurovascular bundle of the prostate was documented under the pubic arch. Two distinct nerve bundles were identified superior to the urethra and medial to the origin of the crural bodies. Nerve bundles were observed to join the corporeal bodies at the penile hilum. Proximal to the penile hilum the dorsal nerves stained only for S-100 and VAChT. From the junction of the crural bodies at the hilum to the glans penis dorsal nerve fibers stained positive for S-100, VAChT and nNOS. Calcitonin gene-related peptide and substance P demonstrated positive staining at the distal nerves, particularly at the glans. In contrast, the whole course of the cavernous nerve stained for S-100 and nNOS. Under the pubic arch at the penile hilum the cavernous nerves were found to convey nNOS positive branches to the dorsal nerve to transform its immunoreactivity to nNOS positive. Proximal nNOS negative perineal nerves were shown to stain positive for nNOS distal on the penis. Interaction between nNOS positive dorsal nerve branches and perineal nerves was at the cavernous-spongiosal junction, where the bulbospongiosus muscle terminates.
• Conclusions: At penile hilum, where the corporeal bodies start to separate, the cavernous nerve sends nNOS positive fibers to join the dorsal nerve of the penis, thereby, changing the functional characteristics of the distal penile dorsal nerve. Similarly the nNOS negative, ventrally located perineal nerve originating from the pudendal nerve becomes nNOS reactive at the cavernous-spongiosal junction. These 2 examples of redundant neuronal wiring in the penis may impact erectile function, especially during reconstructive surgery.
  
• Editorial Comment
  This is another paper that shows again our imperfect knowledge of urogenital innervation. Yucel and Baskin in an elaborate work demonstrate the interaction of both pudendal and dorsal penile nerves with branches of the hypogastric nerves at the level of the base of the penis. All of a sudden we cannot be sure anymore that e.g. the pudendal nerve has only somatic purposes or that branches of the hypogastric plexus are purely autonomic.
  If there exists such an interacting network in an area where we are very close during pelvic floor surgery than the differences of nerve-sparing surgical procedures in the individual patient may become more understandable. Could it be that in some patients where no nerve-sparing procedure is performed collateral nerve supply from other nerves result in good functional outcome with regards to the potency, which is otherwise not explainable?
  We constantly have to refine and sometimes revise old dogmas especially in areas such as pelvic surgery and their anatomy if what we find does not 100% correspond with published schemes. Above all preservation of autonomic nerves does not result in perfect penile functions even in the hands of the best surgeons. And on the other hand deliberate dissection of autonomic nerves may still not lead to erectile dysfunction in all cases. Maybe studies like this one explain one of several possibilities.

Dr. Arnulf Stenzl
Professor and Chairman of Urology
Eberhard-Karls-University Tuebingen
Tuebingen, Germany