Abnormalities of female genitalia
A disturbed fusion of the lower section of the paramesonephric duct (Müller) can lead to a variety of abnormalities in the utero-vaginal region. Such abnormalities in the genital region are almost always associated with such of the urinary tract, since these two systems are closely connected with each other.
As we saw earlier, the absence of AMH leads without fail to a further development of the paramesonephric duct.
Three phases can be distinguished:
- The spread of the paramesonephric duct down to the urogenital sinus.
- The fusion on both sides of the lower third of the paramesonephric duct out of which the uterus and the upper 3/4 of the vagina arise
- The resorption of the dividing wall of the paramesonephric duct on both sides after fusion (end of the 3rd month)
An absent or incomplete migration of the paramesonephric duct in the direction of the SUG is responsible for an atresia and/or complete or incomplete aplasia of the uterus, which is usually associated with renal abnormalities. This syndrome is called the Maye Rokitansky Kuster Hauser syndrome.
A partial or complete failure of the lower parts of the two paramesonephric ducts (Müller) to fuse or an incomplete development (atresia) of one of two paramesonephric ducts is responsible for the formation of a uterus bicornis uni- or bicollis with or without doubling of the vagina. The uterus bicornis unicollis is encountered the most frequently.
The absent resorption of the median dividing wall of the two paramesonephric ducts (Müller) leads to a septated uterus:
- Uterus septus (from the body to the uterine cervix)
- Uterus subseptus (only in the body region)
- Uterus subseptus (only in the cervical region)
When no vaginal plate develops, this leads to a vaginal aplasia that, though, only very rarely occurs in isolation. Due to their partly common origin uterine abnormalities are mostly associated with those of the vagina.
In endometriosis one finds ectopic endometrial tissue outside the uterus, either on the ovaries, the fallopian tube, the uterine ligaments, the recto-vaginal septum, the pelvic peritoneum or possibly in a scar following a laparotomy. Just like the uterine endometrium, this tissue takes part in the menstrual cycle.
There are various theories concerning the origin of this tissue:
- The metaplasia theory maintains that the coelomic epithelium, out of which the paramesonephric duct through invagination has arisen, and formed the fallopian tube, the uterus and parts of the vagina, retained its ability to differentiate and become endometrium.
- The reflux theory holds that scaly endometrial material gets into the abdominal cavity retrogradely and primarily grows into the small pelvic area and only secondarily into the peritoneum.
- The implantation theory says that possibly through an inadvertant transplantation during a surgical intervention endometrial tissue gets outside the uterus and starts to grow there.
- In the engendering of endometriosis genetic, immunologic and hereditary factors probably also play a role. This explains why not all women in whom endometrial cells get into the abdominal cavity are susceptible to the same extent for the formation of an endometriosis.
Absent perforation of the hymen
Missing hymen perforations are rare. During organogenesis a layer of endodermal tissue divides the vagina from the urogenital sinus (future vaginal vestibule). This tissue layer degenerates during the 5th month and leaves only the hymen behind. If this degeneration fails to occur, the hymen perforation does not occur and mucus from the cervical glands, stimulated by the (maternal) estrogen, collects above the hymen. This can lead to a hydrometrocolpos. Sometimes this abnormality manifests itself only in adolescence by a painful amenorrhoea with a hematometrocolpos.