Ovarian endometriosis makes up 50-70% of all cases of endometriosis (Sampson, 1921). Surface lesions of the ovary are similar to the ones of peritoneal endometriosis. Ovarian endometriosis usually assumes a cystic form which is known as endometrioma.
Endometriomas, which are also known as chocolate cysts, usually have a diameter of 1-6 cm, although cysts of up to 25 cm diameter have been also been observed. The small bleeding of ectopic endometrium forms cystic enlargements of haemorrhagic content in the ovaries, which then turns brown or black (chocolate cysts).
Histological confirmation of the ovarian endometriomas is advised when functional glands and stroma are found.
Classification of chocolate cysts
Nezhat et al. (1992), categorized chocolate cysts according to their laparoscopic appearance, the contents of the cyst and the easiness of their removal from ovarian tissue. The histological findings on which this classification is based refer to the observation of endometrial glands and stroma.
The two types of chocolates cysts are:
- Type I (primary endometriomas): they are the true endometriomas and they have the same origin as peritoneal endometriosis,
- Type II (secondary endometriomas): they are cysts of the follicle or the corpus luteum and they filter out from endometriotic implants or from primary endometriomas.
Secondary endometriomas (chocolate cysts), may be of three types: IIA, IIB, IIC and they are cysts larger than primary endometriomas (3-20 cm). Their content varies from haemorrhagic to thick chocolate-like.