Endometriosis is a common, benign, and chronic disease in women of reproductive age that is characterized by the occurrence of endometrial tissue outside the uterus. The etiology of endometriosis is not yet fully established; however, retrograde menstruation is one of several factors involved. Symptoms include dysmenorrhea, dyspareunia, chronic pelvic pain, and infertility. Treatment is based on the individual disease manifestation and may either involve the administration of pain relievers and hormonal therapy or surgical removal of endometriotic tissue. Endometriosis tends to recur, but symptoms and disease spread improve after pregnancy in many cases, as well as in menopause.
- Age of onset: 20–40 years
- Incidence: 2–10% of all women
- Ethnicity: In the US, endometriosis is more common in white and Asian women than in black and Hispanic women.
Epidemiological data refers to the US, unless otherwise specified.
- The etiology of endometriosis is not yet fully understood; however, retrograde menstruation seems to play a major role in the pathogenesis of endometriosis.
- Other contributing factors include:
- In endometriosis, endometrial tissue occurs outside of the uterus.
- Common locations of endometriotic implants include:
- Regardless of where the endometrial tissue is located, it reacts to the hormone cycle; in much the same way as the endometrium and proliferates under the influence of estrogen.
- Endometriotic implants result in:
- Up to one-third of patients are asymptomatic. 
- Chronic pelvic pain that worsens before the onset of menses.
- Uterosacral tenderness, uterosacral nodularity 
- Pre- or postmenstrual bleeding
- Infertility 
Endometriosis may also be asymptomatic in many women and appear as an incidental finding during surgery performed for another reason.
- Patient history
- Rectovaginal tenderness
- Adnexal masses
- Transvaginal ultrasound (best initial test)
- Laparoscopy (confirmatory test) may show endometriotic implants and adhesions
Normally the severity of the findings does not correlate with the severity of symptoms.
- Endometrium: endometrial implants that present as yellow-brown (sometimes reddish-blue) blebs, islands, or pinpoint spots
- Fallopian tubes: salpingitis isthmica nodosa
- Normal endometrial glands
- Normal endometrial stroma
- Preponderance of hemosiderin laden macrophages due to cyclic hemorrhages into endometriomas
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- Definition: benign disease characterized by the occurrence of endometrial tissue within the myometrium due to hyperplasia of the endometrial basal layer
- Epidemiology: peak incidence at 35–50 years
- Etiology: The exact etiology is unknown, though some risk factors have been identified:
- Clinical features
The differential diagnoses listed here are not exhaustive.
- Medical therapy
- First-line: laparoscopic excision and ablation of endometrial implants
Second-line: open surgery with hysterectomy with or without bilateral salpingo-oophorectomy
- Treatment-resistant symptoms
- No desire to bear additional children
- Endometriosis in the uterotubal junction inhibits implantation of the zygote: ↑ risk of ectopic pregnancy 
- Endometriosis → fibrous adhesions → strictures and entrapment of organs
- Endometriosis is associated with a slightly elevated risk of ovarian cancer. 
We list the most important complications. The selection is not exhaustive.