| Jump To |
| Stages and Symptoms |
| Stage 1 — Minimal |
| Stage 2 — Mild |
| Stage 3 — Moderate |
| Stage 4 — Severe |
| Types of Endometrial Lesions |
| Takeaways |
| FAQs |
Endometriosis is a condition in which tissue similar to the lining of the uterus grows outside of it — on the ovaries, fallopian tubes, bowel, bladder, and other pelvic structures. If you have recently been diagnosed or are trying to understand what your doctor has told you, one of the most useful questions to ask is: what does endometriosis look like? The answer depends on the stage, the type of lesions present, and where they have developed — all of which vary considerably from person to person.
According to the World Health Organization, endometriosis affects approximately 10% of women and girls of reproductive age globally — around 190 million people. Despite how common it is, it remains widely misunderstood, partly because it is invisible from the outside and can only be confirmed through surgical investigation.
Researchers and gynaecologists have developed staging systems to describe and classify the extent of endometrial tissue growth — helping patients and physicians visualise what is happening inside the body. According to the Cleveland Clinic, endometriosis tissue can grow anywhere from the space behind the uterus to the ovaries, fallopian tubes, bladder, and in more severe cases, into the intestines and surrounding organs.
Living with a chronic condition like endometriosis has real emotional and psychological dimensions alongside the physical ones. The team at Conway Behavioral Health supports individuals navigating the mental health impacts of chronic pain and long-term illness.
STAGES AND SYMPTOMS
How Stages Relate to Symptoms
One of the most important — and often surprising — things to understand about endometriosis staging is that the stage does not reliably predict how severe your symptoms will be. A person with Stage 1 endometriosis may experience debilitating pelvic pain, while someone with Stage 4 disease may have lived with it for years without knowing, only discovering it during an unrelated investigation or when trying to conceive.
Symptoms of endometriosis can include painful periods, chronic pelvic pain, pain during intercourse, pain with bowel movements or urination, heavy menstrual bleeding, fatigue, and infertility. These symptoms are driven largely by inflammation, hormonal sensitivity of the misplaced tissue, and the formation of scar tissue — not solely by the volume of disease present.
The classification system most widely used by clinicians is the revised American Society for Reproductive Medicine (rASRM) scoring system, originally developed in the 1970s and updated in 1996. As described in research published in Acta Obstetricia et Gynecologica Scandinavica, this system assigns numerical points to lesions based on their size, depth, and location — producing a total score that corresponds to one of four stages. A complementary system introduced in 2021 by the American Association of Gynecologic Laparoscopists (AAGL) focuses specifically on surgical complexity, helping surgeons plan the safest and most effective approach for removing endometrial tissue.
| Stage | Classification | rASRM Score | What It Generally Means |
| Stage 1 | Minimal | 1–5 points | A few small, superficial implants or nodules — limited involvement |
| Stage 2 | Mild | 6–15 points | More implants, some deeper lesions, small adhesions forming |
| Stage 3 | Moderate | 16–40 points | Multiple deep implants, possible endometriomas, adhesions on ovaries and tubes |
| Stage 4 | Severe | Over 40 points | Extensive deep implants, large cysts, dense adhesions — bowel or bladder often involved |
STAGE 1
Stage 1 Endometriosis — Minimal
In Stage 1, or minimal endometriosis, only a small number of superficial endometrial implants are present. These are thin patches of tissue — sometimes described as resembling blisters, powder burns, or small red, brown, or clear spots — attached to the surface of the peritoneum (the membrane lining the pelvic and abdominal cavities) or on the surface of other pelvic organs.
There are typically no significant adhesions (bands of scar tissue) at this stage, and the pelvic anatomy is not distorted. The total rASRM score falls between 1 and 5 points. Despite the minimal appearance of Stage 1 disease, some women experience profound pelvic pain — a reminder that symptoms do not scale with the visible amount of tissue.
Because the implants at this stage are small and may appear clear or translucent rather than the classic ‘powder burn’ colour, they can be easily missed during laparoscopy by a surgeon who does not specialise in endometriosis. This is one reason why diagnosis is often delayed an average of 7–10 years after symptoms first appear.
STAGE 2
Stage 2 Endometriosis — Mild
Stage 2, classified as mild endometriosis, involves a greater number of implants and the beginnings of deeper lesion penetration. The rASRM score falls between 6 and 15 points, which may correspond to several small to medium superficial lesions plus a small number of deeper ones — implants that penetrate more than 5 mm beneath the peritoneal surface.
At this stage, adhesions may begin to form — thin filmy bands of scar tissue that can cause structures within the pelvis to stick together. These are most commonly found in the area behind the uterus known as the cul-de-sac or pouch of Douglas. While the pelvic anatomy is still largely intact, the developing adhesions can begin to cause pain during menstruation and intercourse.
Women with Stage 2 endometriosis may find their symptoms more noticeable than Stage 1 patients, though this is not universal. The increased depth of some lesions means they may be more difficult to remove surgically and more likely to produce the prostaglandins that drive menstrual pain and inflammation.
STAGE 3
Stage 3 Endometriosis — Moderate
At Stage 3, or moderate endometriosis, the disease has progressed to involve multiple deep implants and the formation of more significant adhesions. The rASRM score ranges from 16 to 40 points. What makes Stage 3 visually and clinically distinct is the involvement of the ovaries and fallopian tubes — adhesions now commonly appear attaching the ovaries to surrounding structures, including the uterine wall and pelvic sidewall.
Small endometriomas — ovarian cysts filled with old menstrual blood, sometimes called ‘chocolate cysts’ because of their dark brown appearance — may begin to form at Stage 3. These cysts can range in size from a few millimetres to several centimetres and can significantly impair ovarian function. Their presence is associated with reduced egg quality and lower fertility, making Stage 3 an important threshold for women who are trying or planning to conceive.
The fertility implications of endometriosis, combined with the emotional weight of a chronic diagnosis, can be enormously stressful. For support navigating these challenges, Conway Behavioral Health offers compassionate care for individuals and couples managing chronic health conditions and their impact on mental wellbeing.
STAGE 4
Stage 4 Endometriosis — Severe
Stage 4, or severe endometriosis, represents the most extensive form of the disease, with an rASRM score above 40 points. This stage is characterised by numerous deep endometrial implants, large endometriomas on one or both ovaries, and dense, thick adhesions throughout the pelvic region. At this stage, the normal anatomy of the pelvis can be significantly distorted — organs that should move freely are often bound together by scar tissue.
In severe cases, the bowel and bladder are frequently involved, with endometrial tissue implanting on or penetrating their walls. This can cause symptoms such as painful bowel movements, rectal bleeding during menstruation, frequent urination, and in extreme cases, bowel obstruction. Stage 4 endometriosis typically requires highly specialised surgical expertise to treat, and in many cases a multidisciplinary team including a colorectal surgeon is needed.
Despite the dramatic extent of Stage 4 disease, some women continue to live with it undiagnosed for years because pain and symptom severity can fluctuate. Others present with severe, rapidly progressive symptoms from early in their disease course. The stage captures the physical extent of the disease — not its trajectory or the experience of living with it.
TYPES OF LESIONS
Types of Endometriotic Lesions and What They Look Like
Within each stage, endometriotic lesions can appear in several distinct forms. Understanding these helps explain why endometriosis can be difficult to identify during surgery — not all lesions look the same, and many can be mistaken for other tissue.
| Lesion Type | Appearance | Location | Clinical Significance |
| Superficial peritoneal lesions | Small red, brown, black, white, or clear blisters on the peritoneum surface | Peritoneum, pelvic sidewall, cul-de-sac | Most common; can be missed if translucent or atypical colour |
| Deep infiltrating lesions | Firm nodules that penetrate >5mm below peritoneal surface; often dark and fibrotic | Uterosacral ligaments, bowel, bladder wall, rectovaginal septum | Associated with severe pain; hardest to excise completely |
| Endometriomas (ovarian cysts) | Thick-walled cysts filled with dark, old blood (‘chocolate cysts’) | Ovaries, typically 2–10 cm diameter | Impairs ovarian function; associated with infertility |
| Adhesions | Thin filmy bands (early) or thick, dense fibrous tissue (advanced) | Between ovaries, tubes, uterus, bowel, bladder | Causes organ tethering, pain, and in severe cases bowel/bladder obstruction |
| Powder burn lesions | Small black or dark brown spots resembling ash marks | Peritoneum surface, ovary surface | Classic endometriosis appearance — easier to identify surgically |
How Is Endometriosis Diagnosed?
Endometriosis cannot be definitively diagnosed through blood tests, ultrasound, or MRI alone — though these imaging tools can detect larger endometriomas and help guide clinical suspicion. The gold standard for diagnosis remains laparoscopy: a minimally invasive surgical procedure in which a small camera is inserted through the abdomen to directly visualise the pelvis and identify endometrial implants.
During laparoscopy, the surgeon can both see and take biopsies of suspicious tissue. A histological (microscopic) analysis of the tissue sample provides a definitive diagnosis by confirming the presence of endometrial glands and stroma outside the uterus. In skilled hands, laparoscopy can also be used therapeutically — removing or ablating lesions during the same procedure.
The challenge is that laparoscopy requires anaesthesia and surgical access, meaning it cannot be performed as a routine screening tool. This contributes to the significant diagnostic delay — averaging seven to ten years in many countries — that many people with endometriosis experience.
TAKEAWAYS
Takeaways
Endometriosis looks different in every person and at every stage. From the tiny, easily missed superficial implants of Stage 1 to the dense adhesions, large ovarian cysts, and organ involvement of Stage 4, the disease presents across a wide spectrum — with no reliable correlation between what can be seen surgically and the severity of symptoms experienced.
What matters most is not the stage itself but the impact the disease has on your quality of life, fertility goals, and daily functioning — and working with a gynaecologist experienced in endometriosis to develop a treatment plan that addresses your specific situation. Staging is a tool to help visualise and quantify the disease; it is the starting point of a conversation, not the final word.
If you are managing the emotional and psychological weight of an endometriosis diagnosis, Conway Behavioral Health provides compassionate, evidence-based support for individuals living with chronic health challenges.
FAQS
Frequently Asked Questions
Can you see endometriosis on an ultrasound or MRI?
Ultrasound and MRI can detect larger endometriomas (ovarian cysts) and some deep infiltrating lesions, particularly those involving the bowel or bladder. However, superficial peritoneal implants and thin adhesions are generally not visible on imaging. This means that a normal ultrasound or MRI does not rule out endometriosis. Laparoscopy — direct surgical visualisation — remains the only way to definitively diagnose the full extent of the disease.
Does the stage of endometriosis determine the severity of symptoms?
No — and this is one of the most important things to understand about endometriosis. The surgical stage describes the quantity and location of disease tissue, not how much pain or dysfunction it is causing. Some people with Stage 1 endometriosis experience incapacitating pain while others with Stage 4 have minimal symptoms. The disconnect between visible disease and symptom severity is one of the defining features of endometriosis and one reason why treatment must be tailored to the individual, not just the stage.
What does an endometrioma look like and is it dangerous?
An endometrioma — also called a ‘chocolate cyst’ — is an ovarian cyst filled with old, dark menstrual blood that has accumulated over time. It typically appears on ultrasound as a round, fluid-filled structure with a characteristic ground-glass internal appearance. Endometriomas range from a few millimetres to 10 centimetres or more. While not cancerous, they can impair ovarian function, reduce egg reserve, and significantly affect fertility. Larger endometriomas usually require surgical removal, though the procedure itself carries some risk to ovarian reserve and should be planned carefully.
Can endometriosis be treated without surgery?
Yes — though the most effective long-term management often involves surgical excision of lesions, non-surgical approaches are a first-line option for many patients. Hormonal therapies — including combined oral contraceptives, progestin-only medications, GnRH agonists, and the levonorgestrel IUD — work by suppressing the hormonal stimulation that causes endometrial tissue to grow and bleed. These medications can reduce pain and slow disease progression but do not eliminate existing lesions. Pain management, physiotherapy, and dietary approaches can also support symptom control alongside or instead of hormonal therapy.
Is Stage 4 endometriosis always worse than Stage 1?
In terms of the amount of disease tissue present, yes — Stage 4 involves significantly more implants, deeper penetration, and more extensive adhesion formation than Stage 1. But ‘worse’ in terms of daily life does not always follow that pattern. Pain levels, fertility impact, and quality of life do not reliably correspond to stage. Some people live with Stage 4 disease for decades without severe symptoms; others find Stage 1 profoundly disabling. Treatment decisions should always be guided by symptoms and individual goals, not stage alone.
How long does it take to get diagnosed with endometriosis?
The average diagnostic delay for endometriosis is estimated at seven to ten years in most high-income countries, and longer in settings with limited gynaecological access. This delay occurs because symptoms such as painful periods and pelvic pain are often dismissed as normal or attributed to other conditions, because definitive diagnosis requires surgery, and because awareness among both patients and healthcare providers remains lower than it should be. If you have symptoms that consistently worsen around your menstrual cycle and are not responding to standard pain relief, asking your doctor specifically about endometriosis is a reasonable and important step.