Endometriosis is a common condition affecting around 5 or 10 in 100 women. It is a problem because it can cause pain, scarring and sometimes trouble getting pregnant.

Many women with pelvic pain have endometriosis, or have had endometriosis in the past. However the amount of endometriosis doesn’t fit well with the amount of pain. So, you can have severe endometriosis but no pain – or you can have mild endometriosis and lots of pain.

What is endometriosis?

The lining of the uterus is called Endometrium. This is the tissue that grows inside the uterus each month and bleeds away with a period. When tissue like this is found in other areas around the pelvis, not just inside the uterus, it is called Endometriosis.

The areas of endometriosis are called lesions.

Endometriosis lesions form a spotty covering on the sidewalls of the pelvis, or on the surface of the pelvic organs. More severe endometriosis grows into the pelvic organs themselves or forms round ‘cysts’ called ‘Chocolate Cysts in the ovaries. Most endometriosis lesions can’t be seen on an ultrasound scan.

Endometriosis is a pain you can see at a laparoscopy, but often it is only one part of pelvic pain. Many girls and women with endometriosis have a mix of different symptoms, not just period pain.

For example, many women with endometriosis also have an irritable bowel. While a few of these women have endometriosis lesions in the bowel wall, most don’t. Their bowel looks normal but behaves badly. There are also many women with an irritable bowel who have never had endometriosis.

It is important to remember that there are may types of pain you can’t see.


Women with more severe endometriosis may have an Endometrioma. These are also called chocolate cysts. The cyst contains thick brown fluid and has a thick wall. It grows inside the ovary, making the ovary larger. The following photos were taken at the laparoscopy of a woman with an endometrioma inside both her ovaries. They show:

  • what an endometrioma looks like on ultrasound
  • the brown fluid that comes out when the ovary is opened
  • the cyst wall inside the ovary, and,
  • the cyst wall after it has been removed

The brown fluid gives an endometrioma an even grainy appearance on ultrasound.

At a laparoscopy, opening the endometrioma in the right ovary allows the brown fluid to come out.

The endometrioma in the left ovary has had the brown fluid removed. Now the wall of the cyst needs to be removed from the ovary.