The endometrium is the tissue that lines the uterine cavity, in which the embryo must implant. This is an active tissue (it is not a mere cushion where the embryo implants) and its behavior is decisive for implantation to take place.
Since the endometrium is such an important tissue for the reproductive system, it must be continually renewed. In non-pregnant conditions the endometrium sheds, usually every month, which is known as menstruation.
During menstruation, the endometrium that was formed in the previous cycle is discarded, so that just after menstruation, it is thin, and must grow, by cell proliferation, to generate a new endometrium in which an embryo can be implanted. This proliferation is controlled by the woman's hormonal system, mainly by estrogens, which are mostly secreted in the woman's ovary, during the growth of the follicles, which are on the way to ovulation.
Endometrial hyperplasia is an uncontrolled growth of the endometrium, without this implying malignancy in its cells. It most often (but not always) occurs because of excessive hormonal stimulation, for example, prolonged estrogen secretion or administration. Endometrial hyperplasia, therefore, is nothing more than the situation in which the endometrium produces, as always in the first part of the cycle, before ovulation, cell proliferation and growth of endometrial thickness, but in an excessive and disordered manner. This means that the endometrium tends to be thick, that the achievement of pregnancy is complicated in this cycle (the endometrium is not correctly ordered and balanced cellularly and molecularly speaking) and sometimes, if it is prolonged, it can produce bleeding by spontaneous desquamation, as the endometrium is too thick to be able to remain stable in the uterus. This type of hyperplasia is called simple hyperplasia, is typically seen in fertility centers and is easily controlled with hormonal treatment.
However, if the situation is prolonged without diagnosis and treatment, the cellular disorder is evident, so we speak of complex hyperplasia, in principle without atypia (prolonged and specific medical treatment). The worsening of the hyperplasia will make the shape of the cells no longer normal, so that they begin to resemble tumor cells. This is complex hyperplasia with atypia, which is the stage prior to endometrial cancer, and must be treated promptly by surgery. If the situation persists and the endometrium worsens, endometrial cancer is declared, the treatment of which is much more complex.
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