Endometriosis is a condition where tissues of the endometrium (the inner lining of the uterus) develop elsewhere in the body. Normally this tissue should only be located in the uterus. Endometriosis is most commonly seen in the pelvic area or on other organs in the abdominal cavity, but it may rarely develop in distant organs.
Pelvic pain, often quite severe and particularly just before the onset of periods, and infertility are the most common symptoms for which medical advice is sought. However, although endometriosis is a common gynecological condition, the diagnosis is often missed when the symptoms are mild or when there is no other associated cause requiring investigation, such as infertility. Painful sexual intercourse or irregular heavy periods may also be the presenting complaint.
How does endometriosis occur?
To understand what happens in endometriosis it is helpful to know a little about the physiology of menstruation. The average menstrual cycle is 28 days long, counted from the first day of menstruation to just before the next period.
Various hormones play their part in regulating the menstrual cycle. Gonadotropin releasing hormone (GnRH) secreted by the hypothalamus acts on the pituitary gland to control production of hormones. The pituitary gland produces hormones such as luteinizing hormone (LH) and follicle-stimulating hormone (FSH) which induce ovulation and stimulate the ovaries to produce estrogen and progesterone.
The endometrium varies in thickness at different times of the menstrual cycle due to the action of estrogen and progesterone. Rising estrogen and progesterone levels help to thicken the endometrium and prepare it for embedding of the embryo if fertilization takes place. If pregnancy does not occur, the hormone levels drop and the uterine lining mixed with blood is shed and comes out as menstrual bleeding.
Pathophysiology of Endometriosis
In the case of endometriosis, endometrial tissue is found in other parts of the body besides the uterine lining. It may occur on the uterus, ovaries, fallopian tubes, bladder, bowel, rectum or anywhere else within the pelvis or abdominal cavity. Endometrial tissue may even be seen in distant organs such as the brain or lungs or on Cesarean and episiotomy scars.
Irrespective of the site, these endometrial tissues behave like the endometrial lining of the uterus during a menstrual cycle. The tissues may bleed and break down each month during a menstrual period. This can give rise to formation of adhesions, especially in the pelvis which may be a contributing factor to the pain, a common symptom of endometriosis.
Endometriosis of the ovary can produce a cyst known as endometrioma. Bleeding within it can cause the formation of a chocolate cyst of the ovary.
What causes endometriosis?
The exact cause of endometriosis is unknown but there are various theories regarding the cause :
- Retrograde menstruation – backflow of menstrual blood and endometrial tissue from the uterus through the fallopian tubes into the pelvis and abdomen.
- Endometrial cells carried via the blood stream or lymph vessels to distant organs.
- Direct implantation of cells at the site of surgical scars.
Risk Factors of Endometriosis
Endometriosis may occur at any age in a menstruating woman but is more often seen in women withe one or more of the following risk factors :
- Women in their 30s or 40s.
- Family history may be present.
- More common in Caucasian (white) women than in African American or Asian women.
- Tall, thin women with low body mass index (BMI).
- Women who have not had any children.
- History of chronic pelvic pain.
- Altered immune state.
- Allergies and asthma.