RECONSTRUCTIVE UROLOGY

Neuroanatomy of the male urethra and perineum
Yucel S, Baskin LS
Department of Urology and Paediatrics, UCSF Children’s Medical Center, University of California San Francisco, San Francisco, California, USA
BJU Int. 2003; 92: 624-30

• Objective: To describe the topography of the perineal nerves from their pudendal origin to their course into the male genitalia, with specific attention on the course of the perineal nerve along the ventral penis, including branches into bulbospongiosus muscle and corpus spongiosum.
• Materials and Methods: The study comprised 18 normal human fetal penile specimens at 17.5 - 38 weeks of gestation (determined by fetal heel-to-toe length). Specimens were fixed in formalin, embedded in paraffin wax and serially sectioned at 6 micro m. The penile specimens contained the whole penis from the glans to the crural bodies, beneath the pubic arch and the perineum up to the anal verge. Immunocytochemistry was assessed on selected sections with antibodies against the neuronal markers S-100 and nitric oxide synthase (nNOS). Three-dimensional computer reconstruction of serial sections allowed an in-depth analysis of the neuroanatomy of the fetal penis, perineum and surrounding structures.
• Results: After the pudendal nerve leaves the pudendal canal it gives rise to the perineal nerve branches in the ischiorectal fossa. Perineal nerves travel alongside the ischiocavernous and bulbospongiosus muscles and before reaching the latter, nerve branches course into the bulbospongiosus muscle. During its pathway within this muscle, fine nerve fibres course into the corpus spongiosum by piercing through the junction of the muscle. At the penoscrotal area, the perineal nerves give branches to the scrotum, funnelling into the interscrotal septum. Perineal nerves continue their pathway over the ventral side of penis covering the ventral surface of corpus spongiosum. Branches of the dorsal nerve of the penis at the junction of corpus cavernosum and corpus spongiosum assemble into a network with the perineal nerves. All perineal nerves from their main trunk at the ischiorectal fossa until their interaction with dorsal nerve of penis at the base of penis were nNOS negative. After the interaction with the dorsal nerve of penis, they become nNOS positive.
• Conclusion: Integrating neuroanatomical knowledge about the perineal nerves and their communication with the dorsal nerve of penis should facilitate a strategic approach to reconstructive procedures on the penis. Special care should be taken at the junction between the corpora cavernosa and spongiosa, where the dorsal nerve joins the perineal nerve, and at the proximal bulbospongiosus muscle, thereby protecting the fine nerves piercing into the cavernosa spongiosa.
  
  
• Editorial Comment
  The authors in this paper describe nicely the topography of the pudendal branches supplying the external male genitalia. Although the anatomy of the pudendal nerves have been the subject of reports for almost 2 centuries newly developed surgical techniques and diagnostic procedures as well as findings regarding the pathophysiology of diseases of the external male genitalia and external sphincter have led to new studies looking at the topography of nerve ramifications such as the pudendal nerve and its interaction with the vegetative neural system. Recent papers have specifically looked at the role of pudendal nerve branches both in the male and female external sphincter (1,2). In this manuscript the authors nicely outlined how the perineal branches of the pudendal nerve travel alongside the musculus ischiocavernosus and bulbospongiosus before penetrating the corpus spongiosum. There is also an apparent strong communication between the perineal pudendal nerve branches and the dorsal nerve of the penis at the junction of the corpus cavernosum and the corpus spongiosum.
  These findings are not only important for elucidation of penile diseases or application of local anaesthesia in case of penile surgery, it may also be relevant for the discussion whether afferent sensory nerves from the membranous urethra and the proximal bulbous urethra go alongside the same pathways. According to recent literature (3) sensory afferent nerves from these urethral segments are probably mainly responsible for prevention of the “first drop” incontinence after radical prostatectomy or cystectomy.

References
1. Colleselli K, Stenzl A, Eder R, Strasser H, Poisel S, Bartsch G: The female urethral sphincter: a morphological and topographical study. J Urol. 1998; 160: 49-54.
2. Strasser H, Ninkovic M, Hess M, Bartsch G, Stenzl A: Anatomic and functional studies of the male and female urethral sphincter. World J Urol. 2000; 18: 324-9.
3. Turner WH, Danuser H, Moehrle K, Studer UE: The effect of nerve sparing cystectomy technique on postoperative continence after orthotopic bladder substitution. J Urol. 1997; 158: 2118-22.

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