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What causes malformations of the vagina and uterus?
Last reviewed: 19.10.2021
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Until now, it has not been established exactly what exactly is the origin of the developmental defects of the uterus and vagina. However, the role of hereditary factors, the biological inferiority of cells that form sexual organs, the effects of harmful physical, chemical and biological agents is undoubtedly important.
The emergence of various forms of malformations of the uterus and vagina depends on the pathological effect of teratogenic factors or the realization of hereditary traits in the process of embryogenesis.
According to modern ideas, in all mammals the uterus is formed as a result of the fusion of the Müllerian ducts, but the extent of the merged Mullerian ducts varies: marsupials have a pair of uterus, rodents have an intrauterine partition, most ungulates and predators are bicorn, primates and man have one pear-shaped uterus. It is likely that the shape of the uterus corresponds to the number of embryos developing in it.
There are several theories of the absence or only partial fusion of paired embryonic genital canals (Muller channels). In accordance with one of them, the fusion of the Müllerian channels is due to the translocation of the gene activating the synthesis of the muller-inhibitory substance to the X chromosome, as well as from sporadic gene mutations and teratogenic factors. It is also assumed that the delayed proliferation of the epithelium covering the sexual combs from the side of the coeloma may lead to a breakdown in the formation of the Müllerian strands. As is known, the development of internal and external genitalia by female type is associated with genetically caused loss of tissue reaction to androgens. Therefore, the absence or deficiency of estrogen receptor development in the cells of the Mullerian ducts can inhibit their formation, which leads to changes such as uterine aplasia. A theory of the role of early perforation of the urogenital sinus wall is of particular interest. The pressure in the lumen of the vagina and the Muller channels falls, and one of the causes that lead to the death of the cells of the septum between the parameconephalic channels disappears. Later convergence of the Muller channels with each other and the ingrowth of mesenchymal blood vessels between them leads to the preservation of the cells of the medial walls of the channels and the formation of the septum, the two-horned or double uterus. In addition, the anomalies of the development of neighboring organs - the defects of the urinary system (in 60% of patients) or the disorders of the musculoskeletal system (in 35% of patients with malformations of the uterus and vagina) can interfere with the rapprochement and resorption of the contacting walls of the Muller channels.
Vaginal and uterine developmental defects are often accompanied by malformations of the urinary system, which is explained by the general embryogenesis of the sexual and urinary systems. Depending on the type of genitalia, the frequency of the defects of the urinary system varies from 10 to 100%. In addition, certain types of anomalies of the genitals are accompanied by the corresponding anomalies of the urinary system. Thus, when doubling the uterus and vagina with partial aplasia of one of the vaginas, aplasia of the kidney on the side of the genital mutilation is observed in all patients.
In the absence of conditions for the growth of the Mullerian ducts, complete uterine and vaginal aplasia forms. The prolapse or delayed progression of the urogenital tract to the urogenital sinus forms aplasia of the vagina with the functioning uterus. The length of aplasia is determined by the severity of the delay in the growth of the ducts. According to the literature, complete vaginal aplasia in the presence of the uterus is almost always combined with the aplasia of its neck and cervical canal. Sometimes patients have two rudimentary uterus.
The influence of factors that interfere with the resorption of the walls of the Muller channels leads to the formation of different variants of doubling the uterus and the vagina.