What causes vaginal and uterine malformations?

To date, it has not been established exactly what exactly underlies the occurrence of malformations of the uterus and vagina. However, the role of hereditary factors, biological inferiority of cells that form the genitals, and the impact of harmful physical, chemical, and biological agents is undeniable.

The occurrence of various forms of malformations of the uterus and vagina depends on the pathological influence of teratogenic factors or the implementation of hereditary traits in the process of embryogenesis.

According to modern concepts, the uterus of all mammals is formed as a result of the fusion of the Müllerian ducts, but the length of the fused Müllerian ducts varies: marsupials have a paired uterus, rodents have an intrauterine septum, most ungulates and carnivores have a bicornuate uterus, and primates and humans have a single 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 ducts (Müllerian ducts). According to one of them, the disruption of the fusion of the Müllerian ducts occurs due to the translocation of the gene activating the synthesis of the Müllerian inhibitory substance to the X chromosome, as well as due to sporadic gene mutations and the effects of teratogenic factors. It is also assumed that the disruption of the formation of the Müllerian strands can result in slow proliferation of the epithelium covering the genital ridges from the side of the coelom. As is known, the development of the internal and external genitalia according to the female type is associated with a genetically determined loss of tissue response to androgens. Therefore, the absence or deficiency of estrogen receptors in the cells of the Müllerian ducts can slow down their formation, which leads to such changes as uterine aplasia. Of particular interest is the theory of the role of early perforation of the wall of the urogenital sinus. The pressure in the lumen of the vagina and Müllerian ducts decreases, and one of the causes leading to the death of the cells of the septum between the paramesonephric ducts disappears. Later convergence of the Müllerian ducts 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 ducts and the formation of a septum, a bicornuate or double uterus. In addition, the convergence and resorption of the contacting walls of the Müllerian ducts can be prevented by developmental anomalies of adjacent organs - defects of the urinary system (in 60% of patients) or disorders of the musculoskeletal system (in 35% of patients with developmental defects of the uterus and vagina).

Malformations of the vagina and uterus are often accompanied by malformations of the urinary system, which is explained by the commonality of embryogenesis of the genital and urinary systems. Depending on the type of genital malformation, the frequency of urinary system malformations ranges from 10 to 100%. In addition, certain types of genital anomalies are accompanied by corresponding anomalies of the urinary system. Thus, with duplication of the uterus and vagina with partial aplasia of one of the vaginas, all patients have aplasia of the kidney on the side of the genital malformation.

In the absence of conditions for the growth of the Müllerian ducts, complete aplasia of the uterus and vagina is formed. Prolapse or slow progression of the urogenital tract to the urogenital sinus forms aplasia of the vagina with a functioning uterus. In this case, the extent of aplasia is determined by the severity of the growth retardation of the ducts. According to the literature, complete aplasia of the vagina in the presence of the uterus is almost always combined with aplasia of its cervix and cervical canal. Sometimes, patients have two rudimentary uteruses.

The influence of factors that prevent the resorption of the walls of the Müllerian canals leads to the formation of various variants of duplication of the uterus and vagina.