Endometriosis on ultrasound: what can be seen and what cannot

What endometriosis and adenomyosis are

In endometriosis, tissue similar to the lining of the womb grows outside it: on the pelvic lining, on the ovaries, on the ligaments behind the uterus, and less often on the bowel or bladder. These spots respond to the hormones of the cycle and cause inflammation and adhesions. That explains the main complaints: period pain that gets worse over time, pain during sex and difficulty getting pregnant. Endometriosis affects roughly one in ten women of reproductive age, and the diagnosis often comes years after the first symptoms.

Adenomyosis is a related condition in which this tissue grows into the muscle wall of the uterus. The uterus becomes larger and firmer, and periods are often heavy and painful. The two often occur together, so on the scan I look for signs of both.

What ultrasound shows

A standard transvaginal pelvic scan shows three things that point to endometriosis directly or indirectly.

1. An endometriotic ovarian cyst (endometrioma). It is also called a chocolate cyst because of its thick, dark content. On the screen it is usually a single-chamber (unilocular) cyst with uniform, finely speckled content that looks like ground glass, with almost no blood flow inside. In experienced hands, ultrasound recognises this picture with high accuracy. Unlike a functional cyst, an endometrioma does not go away on its own, so it is not left "until the next cycle" but monitored or treated. How it differs from other cysts is covered in the article on ovarian cysts on ultrasound.

2. Signs of adenomyosis. Using the international MUSA criteria, I look for:

• asymmetry of the uterine walls, when the front and back walls differ clearly in thickness;
• an uneven muscle layer with small cysts and bright islands in the wall;
• fan-shaped shadows spreading out from the wall in stripes;
• a blurred or broken border between the lining and the muscle.

One sign is not enough; the conclusion rests on the combination and on the symptoms. Adenomyosis is sometimes mistaken for a fibroid: a fibroid usually looks like a separate lump with clear edges, while adenomyosis looks like a diffuse change in the wall.

3. Indirect signs of adhesions and deep endometriosis. During the scan I press gently with the probe and watch whether the organs slide against each other. If an ovary does not move, is stuck to the uterus, or both ovaries touch behind the uterus (the so-called kissing ovaries), or pressure on one spot reproduces the familiar pain, that is a reason to suspect adhesions or deep endometriosis.

What ultrasound misses

• Superficial spots on the pelvic lining. This is the most common form of endometriosis, and spots of a few millimetres are not visible on ultrasound. So with typical pain and a normal report, endometriosis is not ruled out.
• The full picture of deep endometriosis. Nodules in the ligaments behind the uterus or in the wall of the bowel or bladder are not always visible on ultrasound. That is why I perform the gynaecological scan following the international IDEA protocol, checking organ mobility, tender spots and nodules. If the extent needs to be clarified, for example before surgery, a pelvic MRI is arranged.
• Activity or "stage" from a single image. Pain bears little relation to the size of the findings: small spots can hurt a lot, and a large cyst may not hurt at all.

A planned scan is best done in the first half of the cycle, on days 5-10, when the lining is thin and the uterine wall is easier to assess. An endometrioma can be seen on any day. If you take hormones, are breastfeeding or have no periods, the scan can be done on any day. How to prepare and what the terms in the report mean are covered in the article on the pelvic ultrasound report, and lining thickness by cycle day in the article on endometrial thickness.

How the diagnosis is made today

It used to be said that there was no diagnosis without laparoscopy. The 2022 guideline of the European Society of Human Reproduction and Embryology (ESHRE) changed this: the diagnosis is based on symptoms, examination and imaging, meaning ultrasound or MRI. Laparoscopy is offered when imaging finds nothing or when treatment without surgery has not helped or is not suitable, and also when surgery is needed for treatment.

Another important change: with typical symptoms, hormonal treatment can start without waiting for final confirmation. There is no blood test that confirms endometriosis. The CA-125 marker can be raised, but it is not recommended for diagnosis: it is normal in many women with endometriosis and rises in other conditions too.

Symptoms worth a visit

• periods so painful that you miss work or study, and painkillers barely help;
• pain that gets worse over the years or started after years of pain-free periods;
• pain during or after sex, especially with deep penetration;
• pelvic pain outside periods, or pain when opening your bowels or passing urine during periods, or blood in urine or stool at that time;
• no pregnancy after a year of regular unprotected sex, or after six months if you are over 35.

Sudden severe lower abdominal pain, especially with fever, vomiting or feeling faint, needs urgent care rather than a planned visit.

Bring previous scan reports and note which days of your cycle the pain comes on. That is how a visit for painful or irregular periods starts: I take your history, examine you and do the pelvic ultrasound straight away.

What next: treatment in brief

Endometriosis is chronic, and the aim of treatment is usually not a permanent cure but less pain and protecting the chance of pregnancy. The mainstay is hormonal medication that suppresses the growth of the spots, plus pain relief. Surgery is discussed for large endometriomas, deep endometriosis involving nearby organs, when medication does not work, when the appearance of a cyst is uncertain, and sometimes for infertility. Surgery on an ovary needs careful thought because it can reduce the ovarian reserve (the egg reserve).

Many women with endometriosis get pregnant on their own. If pregnancy does not happen, I plan the tests and next steps at a pregnancy planning visit. I see patients at ul. Głębocka 9/U1 in Warsaw, no referral needed; booking requires a PESEL number or an identity document.

Quick answers

Sources

The primary sources this text rests on. Links open in a new tab.

1. ESHRE guideline: Endometriosis (2022)European Society of Human Reproduction and Embryology: diagnosis from symptoms and ultrasound or MRI, laparoscopy no longer required, treatment can start without surgery, CA-125 not for diagnosis
2. NICE guideline NG73: Endometriosis, diagnosis and management (2017, updated 2024)UK National Institute for Health and Care Excellence: the symptoms that should raise suspicion and why a normal scan does not rule endometriosis out
3. Guerriero S. et al. Systematic approach to sonographic evaluation of the pelvis in women with suspected endometriosis (IDEA consensus). Ultrasound Obstet Gynecol, 2016international consensus on assessing deep endometriosis by ultrasound, the sliding sign and ovarian mobility
4. MUSA statement: sonographic features of the myometrium. Ultrasound Obstet Gynecol, 2015international agreement on terms: the ultrasound features of adenomyosis
5. WHO: Endometriosis, fact sheetWorld Health Organization: how common endometriosis is, its symptoms and why diagnosis is often delayed

This text describes the general picture and does not replace a consultation. Timings and indications differ from woman to woman and are decided at the appointment, from your history and test results.