Adenomyosis vs Endometriosis: What Is the Difference?

Where exactly is adenomyosis?

The wall of the uterus contains a thick muscular layer called the myometrium.

In adenomyosis, endometrial glands and stroma are found within this muscular wall.

This can cause:

• —enlargement of the uterus
• —thickening or distortion of the myometrium
• —small areas of bleeding within the uterine wall
• —inflammation
• —changes around the junction between the endometrium and myometrium.

Adenomyosis may involve a relatively localised part of the uterus or a wider, diffuse area of the uterine wall.

Where is endometriosis?

Endometriosis occurs outside the normal uterine cavity.

It can involve areas including:

• —ovaries
• —pelvic peritoneum
• —uterosacral ligaments
• —rectovaginal region
• —bowel
• —bladder
• —ureters
• —pelvic sidewalls.

Endometriosis affecting the ovaries may form cysts called endometriomas.

Deep endometriosis can produce fibrotic plaques and distortion of pelvic anatomy.

Can you have both?

Yes.

Adenomyosis and endometriosis frequently coexist.

A 2026 systematic review examining people with both conditions highlighted that combined disease can have an important reproductive burden and may be associated with poorer fertility outcomes than either condition alone.^[5]

Finding one condition therefore does not automatically exclude the other.

Are the symptoms different?

There is substantial overlap.

Adenomyosis commonly causes:

• —heavy menstrual bleeding
• —painful periods
• —pelvic pain
• —pelvic pressure
• —pain during sex.

Endometriosis may cause:

• —severe period pain
• —chronic pelvic pain
• —pain during or after sex
• —painful bowel movements
• —cyclical bowel symptoms
• —urinary symptoms
• —fertility difficulties.

But symptoms do not reliably tell us which condition someone has.

A person with adenomyosis may have symptoms traditionally associated with endometriosis — and vice versa.

Is heavy bleeding more typical of adenomyosis?

Heavy menstrual bleeding is particularly associated with adenomyosis.

Current NICE guidance specifically recommends considering adenomyosis in people with heavy menstrual bleeding accompanied by:

• —significant period pain, or
• —a bulky, tender uterus on examination.^[1]

But heavy bleeding has many other possible causes.

Can adenomyosis cause severe pain?

Yes.

Adenomyosis can cause substantial dysmenorrhoea and chronic pelvic pain.

The amount of abnormality seen on imaging does not necessarily predict exactly how much pain someone experiences.

Pain is influenced by a complex combination of:

• —inflammation
• —nerve signalling
• —uterine contractions
• —coexisting endometriosis
• —central pain processing
• —other pelvic conditions.

How is adenomyosis investigated?

Modern ultrasound and MRI allow adenomyosis to be diagnosed non-invasively in many patients.

Transvaginal ultrasound

For people with heavy menstrual bleeding and suspected adenomyosis, NICE recommends transvaginal ultrasound in preference to transabdominal ultrasound or MRI as the initial imaging test.^[1]

MRI

MRI can be particularly helpful when:

• —ultrasound is inconclusive
• —pelvic anatomy is complex
• —adenomyosis needs further characterisation
• —coexisting endometriosis is suspected
• —detailed pelvic mapping is required.

Systematic reviews suggest both specialist transvaginal ultrasound and MRI have good diagnostic performance for adenomyosis.^[3]

What does adenomyosis look like on ultrasound?

Possible ultrasound appearances include:

• —a globular uterus
• —asymmetrical thickening of the uterine wall
• —small cysts within the myometrium
• —irregularity of the junction between the endometrium and myometrium
• —fan-shaped shadowing
• —abnormal vascular patterns.

No single finding necessarily establishes the diagnosis by itself.

The overall pattern matters.

What does adenomyosis look like on MRI?

MRI provides excellent contrast between different tissues within the uterus.

Features may include:

Junctional-zone abnormality

The inner myometrium — known as the junctional zone — may appear thickened or irregular.

Small myometrial cysts

Tiny high-signal areas can represent ectopic endometrial glands or small haemorrhagic foci.

Ill-defined low T2 signal

Adenomyosis can produce areas of relatively low signal within the uterine muscle because of smooth-muscle hypertrophy and fibrosis.

Globular uterine enlargement

Diffuse adenomyosis can alter the overall uterine shape.

MRI interpretation should consider several features rather than relying on one junctional-zone measurement alone.^[4]

What does endometriosis look like on MRI?

The appearance depends on the type of disease.

Endometriomas

These often contain blood products and typically appear bright on T1-weighted MRI.

They can also demonstrate characteristic T2 shading.

Deep endometriosis

Deep disease often contains substantial fibrosis and may appear relatively dark on T2-weighted imaging.

MRI can help map disease involving structures such as:

• —bowel
• —bladder
• —uterosacral ligaments
• —vagina
• —ureters.

Can ultrasound diagnose both?

Yes.

Specialist transvaginal ultrasound can assess for both adenomyosis and endometriosis.

However, the examination technique and operator expertise matter.

Some forms of superficial endometriosis remain difficult to detect even with high-quality imaging.

Can a normal scan rule them out?

Not completely.

For adenomyosis

Good-quality ultrasound and MRI can be very useful, although imaging appearances vary.

For endometriosis

A normal ultrasound or MRI does not completely exclude endometriosis.

Current NICE guidance states that laparoscopy may still be considered when endometriosis is clinically suspected despite normal imaging.^[2]

This is particularly relevant because superficial endometriosis may not be visible.

Can adenomyosis affect fertility?

Yes.

Adenomyosis has been associated with:

• —reduced pregnancy rates
• —reduced live-birth rates in some populations
• —increased miscarriage risk
• —adverse pregnancy outcomes.

However, fertility is influenced by many other factors including:

• —age
• —ovarian reserve
• —sperm factors
• —tubal function
• —coexisting endometriosis.

Having adenomyosis does not mean pregnancy is impossible.

Can endometriosis affect fertility?

Yes.

Endometriosis is also associated with subfertility.

The mechanisms are complex and may involve:

• —inflammation
• —adhesions
• —ovarian involvement
• —altered pelvic anatomy
• —tubal function
• —ovarian reserve.

Again, many people with endometriosis conceive naturally.

Is the treatment the same?

There is overlap, but treatment is not identical.

Management depends on:

• —predominant symptoms
• —severity
• —fertility plans
• —age
• —previous treatment
• —which condition is present
• —whether both coexist.

How is adenomyosis treated?

For heavy menstrual bleeding with suspected or confirmed adenomyosis, NICE recommends considering a levonorgestrel-releasing intrauterine system — LNG-IUS — as first-line treatment where appropriate.^[1]

Other options can include:

• —tranexamic acid
• —NSAIDs
• —combined hormonal contraception
• —cyclical oral progestogens
• —other specialist hormonal treatments.

Selected patients may be offered procedural or surgical treatments.

Does hysterectomy cure adenomyosis?

Because adenomyosis exists within the uterine wall, hysterectomy removes the organ affected by the disease and is considered the definitive surgical treatment when appropriate.

But it is major surgery and clearly removes the possibility of carrying a future pregnancy.

It is therefore not the right treatment for everybody.

And importantly: a hysterectomy for adenomyosis does not automatically remove endometriosis elsewhere in the pelvis. If endometriosis also exists, that disease needs to be considered separately.

How is endometriosis treated?

Management may include:

• —pain relief
• —hormonal treatment
• —specialist gynaecological management
• —surgery in selected patients
• —fertility treatment where relevant.

Treatment should focus on the individual's symptoms and priorities rather than imaging appearances alone.

Can adenomyosis come back after treatment?

Medical therapies usually suppress symptoms rather than permanently removing adenomyosis.

Symptoms can therefore return when treatment stops.

The behaviour of the condition varies greatly between individuals.

Does adenomyosis disappear after menopause?

Adenomyosis is hormone-responsive and symptoms commonly improve after menopause.

However, individual circumstances vary, particularly in people taking hormonal medication or menopausal hormone therapy.

Persistent or new postmenopausal symptoms should be properly assessed rather than assumed to be adenomyosis.

Adenomyosis vs fibroids

They are different conditions.

Adenomyosis

Abnormal endometrial-type tissue is located within the uterine muscle.

Fibroids

Fibroids are benign tumours composed predominantly of smooth muscle.

Both can cause:

• —heavy periods
• —pressure
• —pain
• —uterine enlargement.

MRI and ultrasound can usually distinguish them, although they may coexist.

The key difference

A simple way to remember it is:

Adenomyosis = within the uterine muscle.

Endometriosis = outside the uterine cavity, usually elsewhere in the pelvis.

But real patients are often more complicated.

You can have adenomyosis + endometriosis + fibroids at the same time.

That is why symptoms and imaging need to be considered together.

Questions to ask your healthcare professional

If adenomyosis or endometriosis has been mentioned, you might ask:

• —Which condition do you think I have?
• —Could I have both?
• —Was adenomyosis seen on my ultrasound or MRI?
• —Was there evidence of deep endometriosis?
• —Were my ovaries normal?
• —Is fertility important when considering my treatment?
• —What are the medical treatment options?
• —Do I need specialist endometriosis assessment?