The endometrium is the lining of the womb, and changes in hormone levels during the menstrual cycle cause first its thickening, then its shedding at the time of a period. Endometriosis occurs when cells similar to those lining the womb are found at sites outside the womb, commonly behind the womb or on the ovaries. Endometriotic tissue also responds to cyclical changes in hormone levels associated with the menstrual cycle. Cyclical bleeding from the deposits occurs, leading to pain, scarring and if the ovaries are involved, cysts can occur.
It has been estimated that endometriosis is present in 10 to 25% of women presenting with gynaecological symptoms in the UK.
The most common symptoms are pelvic pain, often starting before the period, pain with deep penetration at intercourse, and less commonly pain on passing urine or opening the bowel, worse or only at the time of the period.
There appears to be little relationship between the severity of symptoms and the severity of the disease. Treatment can be medical or surgical, or a combination of the two. Surgical treatment consists of cauterising or removing endometriotic deposits. This is done using keyhole (laparoscopic) surgery, usually as a day case procedure. Medical treatment usually starts with simple pain killers, and then hormonal treatments to stop ovulation and thereby prevent the cyclical changes in hormone levels causing menstruation, such as the contraceptive pill, progestogens, and the Mirena IUS.