Endometriosis Etiology and Pathophysiology

The most widely accepted hypothesis is that endometrial cells are transported from the uterine cavity and subsequently become implanted at ectopic sites. Retrograde flow of menstrual tissue through the fallopian tubes could transport endometrial cells intra-abdominally; the lymphatic or circulatory system could transport endometrial cells to distant sites (eg, the pleural cavity). Another hypothesis is coelomic metaplasia: Coelomic epithelium is transformed into endometrium-like glands.

Microscopically, endometriotic implants consist of glands and stroma identical to intrauterine endometrium. These tissues contain estrogen and progesterone receptors and thus usually grow, differentiate, and bleed in response to changes in hormone levels during the menstrual cycle.

Endometriosis

Incidence of endometriosis is increased in 1st-degree relatives of women with endometriosis, suggesting that heredity is a factor. Incidence is also increased in women who delay childbearing, who have shortened menstrual cycles (< 27 days) with menses that are abnormally long (> 8 days), or who have mullerian duct anomalies.