(001) How many Nerve Fibers Innervate the Human Clitoris? A Histomorphometric Evaluation of the Dorsal Nerve of the Clitoris

Abstract

Abstract Introduction It is frequently quoted in mainstream media that the clitoris has “8000 nerve endings”. However, no study has yet quantified the number of nerve fibers (axons) innervating the human clitoris. The dorsal nerve of the clitoris (DNC) is the primary source of somatic clitoral innervation. Reporting the number of axons in the DNC is an important step in our understanding of clitoral innervation and sexual response with implications for many fields of medical practice. Reconstruction following iatrogenic injuries to the dorsal clitoral nerve and restoration following cases of genital mutilation will benefit from a better understanding of the DNC. This knowledge will also be an important factor contributing to the optimization of nerve selection and sensory outcomes in gender-affirming genital surgery. Objective The purpose of this study is to quantify the number of nerve fibers in the human dorsal nerve of the clitoris (DNC) and report the approximate number of nerve fibers that innervate the human clitoris. Methods Following institutional approval and informed consent, dorsal clitoral nerve samples were obtained from 7 transmasculine patients undergoing gender-affirming phalloplasty surgery. In phalloplasty one of the two dorsal clitoral nerves is used to coapt to a sensory nerve in the phallus in order to provide for erogenous phallic sensation. At the time of nerve coaptation, a small excess of dorsal clitoral nerve (5 mm) was collected for analysis at the proximal level of the clitoral body, just after appearance of the dorsal clitoral nerve from underneath the pubic symphysis. The samples were placed into 3% glutaraldehyde fixative, post-fixed in 1% osmium tetroxide and serially dehydrate in ethanol and toluene. They were then embedded in araldite, sectioned on ultramicrotome into 1 μm cross sections and counter-stained with 1% toluidine blue. Histomorphometric evaluation was performed at 1000x magnification using a Leitz Laborlux S microscope and image analysis software (Clemex Vision Professional, Longueuil, Quebec) in order to obtain a nerve fiber count from each dorsal clitoral nerve specimen. Descriptive statistics were performed to yield a mean and range of the number of nerve fibers in the DNC. Assuming anatomic symmetry between bilateral DNC, the total number of somatic nerve fibers innervating the human clitoris was obtained by doubling the mean count of the DNC. Results 7 samples of the DNC were collected. The mean number of nerve fibers in the human dorsal clitoral nerve was 5140 with a range of 4926 to 5543. The mean number of myelinated nerve fibers innervating the human clitoris was 10281 (range 9852 to 11086). Conclusions This study is the first to report the number of myelinated nerve fibers in the human dorsal clitoral nerve and approximate the number of nerve fibers innervating the human clitoris. Findings demonstrate high and consistent myelinated axon counts and density. When taking into account the presence of uncounted unmyelinated axons, it is clear that far more than 8000 fibers innervate the human clitoris. Disclosure No