Endometriosis involves the growth of endometrial-like tissue outside the uterus, typically within the pelvic region, which includes structures like the fallopian tubes, ovaries, and bladder. This tissue behaves like the endometrial tissue that lines the uterus, and can thicken, break down and bleed in response to hormones like estrogen (just as it would during the menstrual cycle). The persistent growth of this tissue leads to inflammation and the development of sticky bands of scar tissue (adhesions) that can adhere pelvic organs together, causing pain and possibly resulting in infertility.
Treatment for endometriosis may involve the surgical removal of larger endometriotic lesions through a technique called laparoscopy, although some lesions might be inaccessible or too small to remove surgically. In this case, hormonal therapies that lower estrogen levels, such as GnRH agonists like Lupron Depot, are used. Since the endometrial-like tissue is estrogen-dependent, these drugs can effectively reduce the size of the lesions and alleviate symptoms.
There are 3 major types of endometriosis: peritoneal/superficial endometriosis, ovarian endometriomas (OMA) or deep infiltrating endometriosis (DIE) (Imperiale et al. 2023).
- Peritoneal endometriosis is the presence of endometriotic lesions on the surface of the lining of the abdominal wall (the peritoneum). It’s found in 15-50% of women with endometriosis and can be diagnosed using laparoscopy (less so with ultrasound and MRI).
- Endometrioma are ovarian cysts that contain dark brown fluid (aka chocolate cysts). It’s found in 50% of women with infertility and can be diagnosed by transvaginal ultrasound and MRI. There are two major types of endometriomas: primary (type I) or secondary (type II). Type I are smaller and more easily removed than type II endometriomas. Type II endometriomas can be further categorized into type IIA, IIB and IIC. (Nezhat et al. 1992)
- DIE are endometriotic lesions that grow below the surface of tissues, and can affect different pelvic organs like the bladder or bowel. It’s present in 20% of women with endometriosis and is diagnosed by transvaginal ultrasound and MRI.
A popular classification system for endometriosis is the revised ASRM (rASRM) classification (ASRM 1997). Using the rASRM system, points are assigned depending on whether or not endometriotic lesions are deep or on the surface, the size of the lesion, and the extent of the adhesions. Stage I is minimal, II is mild, III is moderate and IV is severe. Patients with stage I/II endometriosis will have peritoneal/superficial endometriosis, and patients with III/IV will have ovarian endometriomas and/or DIE.