Sampson’s theory of retrograde menstruation probably explains most of the cases of endometriosis where the implants are located in the pelvic cavity. However, it does not explain some of the rare cases where the implants are located in sites that are some distance from the pelvic cavity — for example, when the endometrial implants are located in the lungs, thighs or arms. In these circumstances it would appear, that living fragments of endometrium somehow enter the veins or the lymph vessels and are transported around the body to another location where they implant in the surrounding tissue.
Accidental transplantation theory-In this situation, the endometrial fragments are transferred from the uterus to the new site during gynaecological surgery or the delivery of a baby. The fragments of endometrium become lodged in the muscle or tissue at the site of the surgical
cut — such as in a caesarian or an episiotomy — where they implant. This theory explains the occurrence of endometriosis in surgical and episiotomy scars. Fortunately, this is not common.
Metaplastic theory-The last theory is known as the metaplastic theory. According to this theory, women may have dormant cells in their pelvic cavities which have the ability to be transformed into endometrial cells in certain circumstances, such as when there is repeated irritation of the lining of the pelvic cavity. This irritation may be due to the presence of menstrual blood, infections or the hormones in the body.
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