Endometriosis is a condition in which endometrial glands and stroma are situated outside the uterus.
In this condition there is cyclical bleeding in the extra uterine endometriotic tissue which causes inflammation and pain during menses.
Endometriosis occurs on the surface of the ovaries, uterine suspensory ligaments, walls of the uterus, fallopian tubes, and the peritoneal surfaces of the pouch of douglas. Other sites can be vagina, bladder, cervix, intestines, caesarean scars, abdominal scars etc.
Endometriosis can be superficial with <5mm depth of penetration from surface or deep >5mm depth of penetration with fibrosis and muscular hyperplasia.
Ovaries are the most common sites of endometriosis and are frequently involved with multiple and bilateral lesions.
Classic sonographic appearance of an endometrioma (ovarian endometriosis) or chocolate cyst is homogenous and hypoechoic lesion with low to medium level echoes and no internal level echoes and no internal vascularity ie ground glass appearance.
Occasionally it can appear completely anechoic resembling simple ovarian cyst or fluid–fluid levels with thickened wall and mural or central calcifications.
Chronic endometrioma (long standing endometrioma) may mimic solid ovarian tumours.