Endometriosis lesions are areas of tissue similar to the lining of the uterus found outside the uterus.
They may also be called endometriosis implants, endometriotic lesions or endometriosis deposits. These words are often used in medical appointments, scan reports or surgery notes, so it can help to understand what they mean.
A lesion is not just “normal period tissue in the wrong place”. Endometriosis tissue is similar to the lining of the uterus, but it is not identical. It can behave differently, interact with the immune system, cause inflammation, and affect nearby organs, tissues and nerves.
What do lesions do?
Endometriosis lesions can cause irritation and inflammation.
Over time, they may contribute to:
- pain
- swelling or irritation in nearby tissue
- scar tissue
- adhesions
- cysts called endometriomas
- nerve irritation
- bowel symptoms
- bladder symptoms
- pain during or after sex
- fertility difficulties for some people
- reduced quality of life
Not everyone with endometriosis has the same symptoms. Symptoms can depend on where lesions are, how deep they are, whether adhesions are present, and how the body responds.
What can lesions look like?
Endometriosis lesions can look different from person to person.
During surgery, they may appear in different colours and forms. Some may be:
- clear
- red
- blue
- black
- brown
- white
- yellowish
- flat
- raised
- puckered
- scar-like
- nodular
- deep under the surface
Some lesions are easy for an experienced surgeon to recognise. Others can be subtle and easier to miss, especially if they are clear, white, hidden under scarring, or located in difficult areas.
This is one reason specialist experience can matter.
Are all lesions the same?
No.
Endometriosis lesions can vary in type, depth and location.
Broadly, endometriosis may include:
- superficial peritoneal lesions
- deep endometriosis
- ovarian endometriomas
- extra-pelvic endometriosis
- scar or abdominal wall endometriosis
These categories are helpful, but real disease can be more complex. A person may have more than one type.
Superficial peritoneal lesions
Superficial lesions are found on the surface of tissues, such as the lining of the pelvis or abdomen.
They may still cause significant pain and inflammation. “Superficial” does not mean “mild” or “not important”. A person’s symptoms should never be dismissed only because disease is described as superficial.
Deep endometriosis
Deep endometriosis grows more deeply into tissue.
It may involve areas such as:
- bowel
- bladder
- ureters
- uterosacral ligaments
- rectovaginal area
- pelvic sidewall
- nerves or nearby structures
Deep endometriosis may need specialist assessment and sometimes multidisciplinary care, depending on the organs or tissues involved.
Endometriomas
Endometriomas are cysts linked with endometriosis, usually found on the ovaries.
They can contain old blood and may be associated with pain, inflammation and fertility concerns for some people.
Endometriomas need careful assessment because treatment decisions can depend on symptoms, size, ovarian reserve, fertility goals and wider disease picture.
Extra-pelvic lesions
Endometriosis lesions can also be found outside the pelvis.
They may involve areas such as:
- diaphragm
- lungs or chest cavity
- bowel
- bladder or urinary tract
- abdominal wall
- surgical scars
- belly button
- sciatic nerve or nearby nerves
- other extra-pelvic sites
Symptoms may depend on the location. For example, thoracic involvement may be linked with chest or shoulder symptoms, while sciatic involvement may be linked with leg pain, numbness or weakness.
Can small lesions cause severe symptoms?
Yes.
The amount of visible disease does not always match the amount of pain or impact.
A person with a small number of lesions may have severe pain. A person with more widespread visible disease may have fewer symptoms. Pain can be influenced by inflammation, nerve involvement, pelvic floor muscle response, adhesions, previous surgery, other conditions and pain processing.
This means symptoms should be taken seriously even if imaging is normal or findings appear limited.
Can lesions be seen on scans?
Some types of endometriosis can be seen on specialist ultrasound or MRI, especially deep disease or endometriomas.
However, not all lesions are visible on scans. Superficial lesions may be difficult to detect with imaging. A normal ultrasound or MRI does not always rule out endometriosis.
If symptoms continue, further assessment or referral may still be needed.
What is the difference between a lesion and an adhesion?
A lesion is an area of endometriosis tissue.
An adhesion is scar-like tissue that can make organs or tissues stick together.
Lesions can contribute to inflammation and scarring, which may lead to adhesions. A person may have lesions, adhesions or both.
What is excision?
Excision is a surgical technique where endometriosis lesions are cut out and removed.
This is different from ablation, where tissue is destroyed on the surface using heat or energy.
The right treatment depends on the person, symptoms, disease location, fertility goals, previous treatment and specialist advice. Surgery should be discussed carefully with a healthcare professional experienced in endometriosis care.
Questions to ask about lesions
If a healthcare professional mentions lesions, you may want to ask:
- Where are the lesions?
- Are they superficial or deep?
- Are any organs involved?
- Is there bowel, bladder, ureter, diaphragm or nerve involvement?
- Are there adhesions?
- Are there endometriomas?
- Can the lesions be seen on imaging?
- Would specialist imaging help?
- Would a multidisciplinary team be needed?
- What treatment options are appropriate?
- If surgery is being discussed, will lesions be excised, ablated or both?
- Will tissue be sent for histology?
Final reminder
Endometriosis lesions are not simply “period tissue in the wrong place”. They are part of a complex inflammatory disease that can affect different tissues, organs and body systems.
Understanding lesion language can help you make sense of scan reports, surgery notes and specialist appointments.
Use our Prepare for Appointment Tool to write down your questions before you speak with a healthcare professional.