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Neurovascular Anatomy of The Developing Human Fetal Penis and Clitoris
Sena Aksel, Medical Doctor, Amber Derpinghaus, Master of Science, Mei Cao, Medical Doctor, Yi Li, Medical Doctor, Gerald Cunha, Doctor of Philisophy, Laurence Baskin, Medical Doctor.
University of California San Francisco, San Francisco, CA, USA.

Background: The human fetal genital tubercle is ambisexual until 8-9 weeks of fetal age(FA). In males, under the influence of androgens the urethral folds of the urethral groove fuse in the midline to form a tubular urethra. In females, fusion process doesn't occur, resulting in an open vestibular groove. We hypothesize that there is a difference between the neurovascular anatomy of the penis and clitoris between 8 to 12 weeks FA(Fig. 1) , which may explain the androgen dependent fusion in males. Methods: 5 normal fetal penises and 5 normal fetal clitorises from 8 to 12 weeks FA were collected from anonymous donors with IRB approval. A modified Visikol HISTO protocol was used to stain for PGP9.5, a neuronal marker and CD 31, an endothelial marker. Specimens were imaged using confocal microscope.Results: A difference in dorsal-to-ventral patterning of radiating vessels was observed between the sexes. In the penis, circumference vessels that are anastomosing at ventral shaft of the penis are parallel to each other. In contrast, in clitoris, dorsal-to-ventral radiating vessels are in a reticular pattern, profusely anastomosing with each other(Fig. 2). In both sexes dorsal vessels travel vertically along the shaft of the genital tubercle as well as circumferentially. These vessels give numerous distal branches as they reach the glans. Dorsal nerves radiate parallel to corporal bodies and with direct contact to the tunica of the corporal bodies. In the penis, dorsal vessels radiate ventrally to form penile raphe where fusion occurs beginning fromof the urethral groove begins at 9 weeks of FA. In the clitoris, ventrally radiated vessels do not fuse and vestibular groove stays open. At 11 weeks FA we noted a clitoral ridge that is occupying vestibular groove. In the penis, co-expression of CD31 and PGP 9.5 is noted at the fusion point that begins at proximal shaft on 10 weeks FA. The area of co-expression follows distally and is only noted only where the active fusion is occurring(Fig. 3). Conclusion: Herein, we present a 3D ontogeny of the human fetal external genitalia using confocal microscopy that provides a new perspective on the differences between the vascular and neuronal development in the human fetal penis and clitoris.
Fig. 1: Confocal Imaging of the human fetal clitoris and penis from 8 to 12 weeks gestation immunostained with CD31 and PGP9.5.
Figure 2: CD31 staining of 11 week penis and clitoris.Figure 3: Electron microscopy(A) and confocal fluorescent immunostaining with CD31(B), PGP9.5(C), and merged channel(D) of a 10 week fetal age penis.



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