Retrograde menstruation occurs when menstrual blood and uterine tissue enters the peritoneal cavity by flowing through the fallopian tubes. The possible relationship between this phenomenon and endometriosis was first described by Dr. John Sampson in the 1920s, and this theory prevailed for decades.
Physicians later realized, however, that most women actually experience retrograde menstruation, while very few develop symptoms or evidence of endometriosis. The cause of endometriosis could not have been due simply to the presence of uterine cells that had migrated outside the uterus. As explained by endometriosis.org, endometriosis has also been found in women who have had a hysterectomy and very rarely in men who have been treated with estrogen therapy.
Possible Causes of Endometriosis
While it is known that endometrial cells outside the uterus can attach to a blood source and proliferate, the reason this occurs in some women and not others is poorly understood. The New England Journal of Medicine states that 1 in 10 women have endometriosis, but in women with pelvic pain or infertility, this number rises to 5 in 10. As the Endometriosis Foundation of America points out, neither physicians nor researchers have agreed on a single cause for endometriosis, and many feel that it may be a combination of factors. According to the journal Reproductive Biology and Endocrinology, some of the prevailing theories are:
- Inflammation and Immune Dysfunction: Patients with endometriosis have been found to have increased inflammatory markers in their peritoneal fluid. An "exaggerated immune response" may lead to the inflammation that is observed in women with endometriosis. However, it is unknown whether the inflammation causes or is caused by endometriosis. A normal immune system should clear endometrial cells from the peritoneal cavity, but since only a small proportion of women develop endometriosis, these women may have a "defective cellular immunity" that prevents their bodies from clearing these cells.
- Vascular Endothelial Growth Factor: This theory posits that endometrial cells may experience increased angiogenesis driven by vascular endothelial growth factor (VEGF), which has been found in high concentrations in some women with "moderate to severe endometriosis."
- Genetic Predisposition: It is not well-understood but still accepted that women have a greater chance of being diagnosed with endometriosis if they have a relative with the same condition.
Why Sampson's Theory Cannot Stand Alone
When it comes to endometriosis and menstruation, many agree that retrograde menstruation allows endometrial cells to enter the ectopic space, but exactly why these cells transplant and proliferate is not understood. As the Endometriosis Foundation of America points out, endometriosis does not always increase in severity over time, as one might expect, from years of endometrial tissue sloughing off in the ectopic space.
Endometriosis can only be definitively diagnosed and staged through surgical means. As the NEJM article explains, noninvasive modes of imaging such as ultrasound and MRI are not sufficiently sensitive or specific enough to detect the hallmarks of endometriosis within the peritoneal cavity. However, these modalities work well for detecting ovarian endometriomas, and the addition of Doppler during a transvaginal ultrasound exam may help to differentiate normal and abnormal tissue by evaluating blood flow within the structures.
Women with endometriosis often suffer with pain and complications for many years before they are formally diagnosed with the condition. While the reasons that any particular woman develops endometriosis may not be clear, each patient deserves a thorough evaluation to help understand and overcome this complex diagnosis in the best possible way.