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Establishment of the autonomic neuroanatomy to the vulval erectile tissues Penhale, Shona Marie Louise


Erectile tissues are the vascular structures within the vulva that fill with blood and are an integral component of the woman's sexual response. Despite the importance of these structures to her sexual function, the detailed neuroanatomical pathways of the autonomic nerves underlying this mechanism of vascular congestion, have not been elucidated. Therefore, this research had been designed to identify the missing components to answer the question: "What is the pathway of the nerves running from the female pelvic plexus to the external genitalia?". In the male, the autonomic innervation of the erectile tissue in the penis has been fully described such that damage from surgery can be avoided or minimized whenever possible. The cavernosal nerves arise from the prostatic plexus and pierce the urogenital diaphragm (UGD) to supply the erectile tissue of the cavernosal bodies. In contrast, the description of the innervation of the female erectile tissue is much less complete and there are no descriptions of the nerves between the vaginal plexus and the "anterior parts". Specifically, their origin from the vaginal plexus and their precise path to the erectile structures of the vulva are unknown and any similarities to male cavernosal nerves are unknown. Additionally, whether or not there are individual branches to the specific erectile structures, which include the right and left clitoral corpora, bisected vestibular bulb and periurethral tissues is also unclear. Utilizing cadaver tissue, the complete pathway of the cavernous nerve in the female was examined using several methods. Using gross dissection of intact pelvises I identified previously well documented structures of the reproductive organs, major pelvic vasculature, the pelvic promontory, the sacral nerves, the sympathetic chain ganglia, the superior hypogastric plexus (SHP), the inferior hypogastric plexus, and the pelvic splanchnic nerves. The putative cavernous nerve was then identified on the lateral wall of the vagina at the level of the vesicouterine pouch. At this point it coursed inferiorly along with the vagina and urethra towards the muscular urogenital diaphragm (UGD). During the inferior course it moved anteriorly into the dense connective tissue between the urethra and vagina and ended up 5 mm lateral to the urethra at the level of the UGD. Previously the cavernous nerve was described as a single, large, easily dissected nerve within the erectile tissue that surrounds the periurethral sponge. In contrast, serial sectioning followed by histological analysis allowed me to determine that the cavernous nerve was most commonly a single nerve bundle that branched into 2-5 smaller nerves upon piercing the UGD. Several branches then coursed laterally, came within 1 mm of the pudendal nerve, and innervated the crua; more medial branches carried on in their orientation to feed the vestibular bulbs. In both serial sectioning and marco dissection I was able to identify differences from previously documented structural anatomy of the bisected vestibular bulbs. We found all our specimens to have much more erectile tissue of the bulbs continue around the anterior wall of the urethra in the shape of an inverted "u". No evidence of the 'bisected' nature of the bulbs was found, as well the bulbs had more fullness of depth than previously documented. This research has provided a more detailed description of the pathway of the autonomic innervation as it passes through the pelvis to the external genitals than had been previously described in the literature. In particular the course of the cavernous nerve as it passes along the lateral wall of the vagina to pierce the UGD and branch to feed the various erectile tissues. This detailed description should enable the necessary immunohistochemical studies to confirm nerve content. It has also raised questions about the previously established bisected structure of the vestibular bulbs which may have significant implications for engorgment in sexual arousal.

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