What is the pathogenesis of endometrioma/endometriosis?

Updated: Dec 14, 2018
  • Author: Shawn Daly, MD; Chief Editor: Eugene C Lin, MD  more...
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Two main theories exist for the pathogenesis of endometriosis. One theory is that endometrial tissue is spread by retrograde menstruation or by vascular and/or lymphatic spread. The second theory holds that the serosal epithelium of the peritoneum undergoes metaplastic differentiation into endometrium-like tissue.

The theory that retrograde menstruation causes endometriosis is supported by the analysis of peritoneal fluid in women. [6] As many as 90% of women have blood in the peritoneal fluid during the perimenstrual period. In addition, endometrial cells have been found in the peritoneal fluid. The pattern of endometriosis is consistent with retrograde menstruation and is most common in the ovary, followed by the other dependent areas of the pelvis. Vascular and/or lymphatic spread is supported by noting the occasional distal (extraperitoneal) sites of endometriosis, including the lungs and central nervous system (CNS). [7] In addition, teenage girls with obstructive uterine or vaginal anomalies show retrograde menstrual bleeding, and endometriosis is common in these patients.

Metaplasia is the conversion of peritoneal epithelium into endometrial epithelium. The theory that metaplasia causes endometriosis is supported by the fact that endometrial cells and peritoneal cells derive from the same celomic wall epithelium. [7] This theory also is supported by development of endometriosis in women who lack normal endometrial tissue, such as those with Turner syndrome or uterine agenesis. In addition, rare cases of endometriosis have been found in the prostatic utricle of men.

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