Stages of endometriosis

Stages and types of endometriosis

Endometriosis is classified into stages and types according to the extent, location and depth of lesions. Classification helps doctors plan treatment, compare outcomes and communicate about disease severity. As the lead author of the World Endometriosis Society (WES) consensus noted: "Classification of endometriosis has remained as enigmatic as the disease itself." For this reason, several complementary systems exist today.

Three main types of endometriosis

Before staging, it is important to distinguish which type of endometriosis is present - each type behaves differently, causes different symptoms and requires a different treatment approach:

1. Peritoneal endometriosis

Superficial lesions on the peritoneum - the thin membrane lining the abdominal cavity and covering the pelvic organs. The most common type, but almost invisible on standard ultrasound. May be minimal yet cause significant pain.

2. Endometriomas (ovarian endometriosis)

Cysts on the ovaries filled with old dark blood - hence also known as "chocolate cysts". Reliably detectable on ultrasound and among the most commonly diagnosed forms of endometriosis for exactly this reason. They damage healthy ovarian tissue and reduce egg reserve.

3. Deep infiltrating endometriosis (DIE)

The most severe type - lesions penetrate more than 5 mm below the peritoneal surface and may grow into the rectovaginal septum, bowel, bladder or ureters. Causes the most intense pain and requires specialist surgical treatment at highly specialised care centres.

ASRM classification - stages I to IV

The most widely used classification was developed by the American Society for Reproductive Medicine - the revised ASRM. The WES consensus published in Human Reproduction (2017) recommends it for use in all cases of endometriosis.

Each stage is assigned a point score based on where and how deeply lesions lie, cyst size and extent of adhesions:

Stage I - Minimal (1-5 points)

Isolated superficial lesions, no or minimal adhesions. Lesions are small and most commonly found on the peritoneum or ovaries. Despite being the mildest form, pain may be just as severe as in more advanced stages.

Stage II - Mild (6-15 points)

More lesions, some deeper, but still without significant adhesions. Lesions may be on the ovaries, fallopian tubes or the space behind the uterus.

Stage III - Moderate (16-40 points)

Numerous lesions, at least one endometrioma on the ovary and more pronounced adhesions. Adhesions begin to affect the function of fallopian tubes and ovaries. At this stage, endometriosis begins to manifest as fertility problems.

Stage IV - Severe (over 40 points)

Extensive disease with large endometriomas, deep lesions and firm adhesions. Adhesions may connect the bowel, ovaries or bladder to the uterus or pelvic wall. This stage requires specialist surgical treatment.

Enzian classification - for deep endometriosis

For women with deep infiltrating endometriosis, the WES consensus recommends the Enzian classification. This more precisely describes the extent of deep endometriosis in individual anatomical compartments - the rectovaginal septum, bowel, urinary system and other structures. It helps the surgeon plan the operation more precisely and estimate its complexity.

Endometriosis Fertility Index (EFI) - for women planning pregnancy

For women who are interested in pregnancy, the WES consensus recommends the Endometriosis Fertility Index (EFI). Unlike the ASRM classification, the EFI takes into account factors directly relevant to fertility - the state of the fallopian tubes, ovaries and laparoscopy results - and helps estimate the chance of natural conception after surgery.

What stage does not mean

Classification staging is useful for surgeons and treatment planning, but has important limitations:

• Stage does not correspond to pain - a woman at stage I may have more severe pain than a woman at stage IV. Pain intensity depends on lesion location, nerve sensitivity and other individual factors.
• Stage does not correspond to fertility - not every woman at stage IV has fertility problems. The type of endometriosis (particularly fallopian tube and ovarian involvement) matters more than the stage itself.
• Stage can change - after surgery or hormonal treatment, disease extent may decrease. Without treatment or after it is stopped, the stage may progress.
• Stage does not determine treatment on its own - symptoms, the patient's wishes, type of endometriosis and the overall clinical picture are the deciding factors.

How is stage and type determined?

The precise type and stage can be determined at laparoscopy - a minimally invasive surgical procedure in which the doctor directly visualises the lesions and can simultaneously remove them. Before surgery, the following help:

• Specialist ultrasound - detects endometriomas and more extensive deep endometriosis
• MRI - provides detailed imaging of deep endometriosis, bowel or urinary tract involvement, and helps plan surgery

Further information on classification: World Endometriosis Society - Classification.