Fetal topographical anatomy of the female urethra and descending vagina : A histological study of the early human fetal urethra

女性尿道と膣の形成に関する局所解剖 : ヒト胎児を用いた組織学的研究

Masumoto Hiroshi

Background: Which parts of the male urethra correspond to the female urethra? To resolve this question, we need to understand fetal topographical changes in the urethra, its external sphincter and vagina. The vagina joins the mid-course of the primitive urethra and, later “descends” to the vaginal vestibulum. Methods: We examined histological sections of 14 female and 4 male mid-term fetuses. Results: The inferior end of the vagina was consistently embedded in the posterior wall of the urethra at 9-12 weeks. The supero-inferior level of the vaginal merging was lower in larger fetuses. Thus, the sequential variation in levels appeared to reflect the process of vaginal descent. However, in spite of penetration of the vaginal end into the posterior urethral wall, we found no sign of destruction of the urethral wall after vaginal descent in the low-merging types. Before vaginal descent, the female external sphincter extended posterolaterally around the urethra. Conclusion: The vaginal descent is classically regarded as a relative topographical change, but it is likely to be a result of elongation of the proximal urethra in the superior side of the vaginal merging. Conversely, the distal urethra is likely to be incorporated into the vaginal vestibulum by 15 weeks. During these processes, most of the female external sphincter seems to be expelled from the original anterior position into the vestibular wall as the urethrovaginal sphincter. The adult female urethra seems to correspond to the male prostatic urethra superior to the prostatic colliculus.

Female uretha

Urogenital sinus

Wollfian duct

Mullerian duct

Prostatic colliculus

External urethral sphincter

Human fetus

Medical sciences [ 490 ]

eng

Hiroshi Masumoto, Jose Francisco Rodriguez-Vazquez, Samuel Verdugo-Lopez, Gen Murakami, Akio Matsubara; Fetal topographical anatomy of the female urethra and descending vagina: A histological study of the early human fetal urethra; Annals of Anatomy - Anatomischer Anzeiger, Volume 193, Issue 6, 20 December 2011, Pages 500-508 (DOI: 10.1016/j.aanat.2011.03.010) references

[DOI] http://doi.org/10.1016/j.aanat.2011.03.010 references

広島大学