What Type of Ultrasound Is Used to Check for Endometriosis?

Around 1 in 10 women of reproductive age in the UK are affected by endometriosis. Despite this however, it typically takes women 8-10 years from their first symptoms to get a confirmed diagnosis. One of the main reasons for that delay is the lack of specialised imaging early on. If your GP or gynaecologist thinks you may have endometriosis, they will most likely order an ultrasound scan first. However, not all ultrasounds are created equal when it comes to diagnosing endometriosis.

We’ll go through what each type of scan can and can’t show you.

What Is an Endometriosis Ultrasound?

An endometriosis ultrasound is an imaging scan that uses sound waves to create moving pictures of your pelvic organs. It allows clinicians to check for signs of endometriosis including cysts on your ovaries, tissue nodules and abnormal tissue growth caused by endometriosis.

Ultrasound cannot definitively diagnose endometriosis, a laparoscopy (keyhole surgery) is needed to confirm a diagnosis. However, a high quality scan administered by a skilled clinician can provide your medical team with valuable information and allow them to fast-track you towards treatment.

There are two types of pelvic ultrasound scans commonly used in gynaecological practice and another type that is useful for bowel-related endometriosis.

The Two Main Types of Ultrasound for Endometriosis

1. Transvaginal Ultrasound (TVS) — the Gold Standard

A transvaginal ultrasound, often called a TVS or TVUS, is the preferred type of ultrasound for endometriosis in the UK and internationally. During the scan, a slim, smooth probe covered in gel is gently placed inside the vagina. It sends sound waves directly towards the uterus, ovaries, and surrounding pelvic structures.

Here is why transvaginal ultrasound is so effective:

• Proximity to the target organs. Because the probe sits close to the uterus and ovaries, it produces far clearer, more detailed images than scanning from the outside of the abdomen.

• Detection of ovarian endometriomas. These "chocolate cysts" fluid-filled cysts on the ovaries appear as thick-walled structures with low-level internal echoes. TVS identifies these with high accuracy.

• Assessment of deep infiltrating endometriosis (DIE). This is the most severe form of the disease, where endometriotic tissue grows into organs such as the bladder, ureters, bowel, or uterosacral ligaments. In the hands of a trained specialist, transvaginal ultrasound can identify DIE lesions and map their location before surgery.

• Dynamic assessment. Unlike static imaging such as MRI, a TVS allows the clinician to apply gentle pressure during the scan assessing whether organs move freely or are stuck together by adhesions (the "sliding sign").

The new NICE guideline 2024 update (NG73) strengthened their original guidance by stating that transvaginal ultrasound scan should be offered to all women with suspected endometriosis rather than offering if appropriate as considered originally. The change comes as efforts to address lengthy waits for diagnosis continue across the UK.

What does the scan involve? The probe is inserted into the vagina with your consent. You will typically be asked to empty your bladder beforehand. The scan takes around 20 to 30 minutes. You may feel mild pressure but it should not be painful. If a TVS is not suitable for you for instance if you have not had sexual intercourse or find vaginal examination distressing your clinician should discuss alternatives.

2. Transabdominal Ultrasound (TAS)

Transabdominal ultrasound involves passing a handheld probe over the surface of your lower abdomen. You will usually be asked to drink water before the scan so that your bladder is full, helping to push your uterus and ovaries into view. This gives a wider view of the pelvis and is good at detecting larger organs or structures, like large ovarian cysts or a greatly enlarged uterus. Routine antenatal scanning is performed this way. 

For endometriosis specifically, a transabdominal scan has clear limitations:

• It cannot visualise the back of the uterus well. The majority of deep endometriosis sits in the posterior pelvis directly behind the uterus, an area that a transabdominal probe cannot reach clearly.

• It misses smaller lesions, particularly those in the pouch of Douglas, on the uterosacral ligaments, or along the bowel.

According to the NICE guideline (NG73, 2024), a transabdominal ultrasound should only be offered when a transvaginal scan is declined or unsuitable. It is a secondary option, not a replacement. If a transabdominal scan returns a normal result, that does not rule out endometriosis.

Expert Transvaginal Ultrasound vs. Routine Ultrasound — a Crucial Difference

A thing that often shocks people when they learn it: all transvaginal ultrasounds are not created equal. Transvaginal ultrasound image quality very much depends on the skillset and expertise of the individual performing the scan.

Published in the journal Abdominal Radiology, this study compared routine transvaginal ultrasound to expert-guided transvaginal ultrasound (ETVUS), both in women who went on to have histologically confirmed endometriosis at surgery. The routine ultrasound identified disease in just 25% of cases. Expert guided ultrasound identified endometriosis in 78% of cases. Thats three times more accurate. 

That’s why the NICE guidance 2024 update was very clear: specialist transvaginal ultrasound scans must be performed by a clinician who plans and interprets the scan AND has specialist expertise in gynaecological imaging. An expert clinician knows to meticulously interrogate the anterior compartment (bladder, ureters) and posterior compartment (uterosacral ligaments, rectovaginal septum, bowel) and not just casually assess the uterus and ovaries.

All of our ultrasound scans performed by myGynaePlus are undertaken by senior clinicians who specialise in gynaecological imaging NOT generalist sonographers. This is a key difference when assessing for conditions like endometriosis.

What Can an Endometriosis Ultrasound Detect?

A well-performed specialist transvaginal ultrasound can identify:

• Ovarian endometriomas — thick-walled ovarian cysts with characteristic dark internal fluid, sometimes called "chocolate cysts"

• Deep infiltrating endometriosis (DIE) — nodules embedded in the bladder wall, uterosacral ligaments, vagina, or rectosigmoid colon

• Adhesions — abnormal tissue connections between organs, which affect how they move during the scan

• "Kissing ovaries" — bilateral ovarian endometriomas lying close together in the pouch of Douglas, often a marker of more widespread disease

• Structural changes — a retroverted or fixed uterus that does not move freely, which can indicate deep posterior disease

What an Ultrasound Cannot Detect

Superficial peritoneal endometriosis small, flat deposits on the surface of pelvic organs have no measurable mass. These lesions cannot be seen on any type of ultrasound. Only a laparoscopy can identify them. This is why a normal ultrasound scan does not rule out endometriosis.

When Is MRI Used Instead?

Magnetic resonance imaging (MRI) is sometimes used alongside or instead of ultrasound when:

• A transvaginal ultrasound is not possible or declined

• The extent of deep bowel or bladder endometriosis needs precise mapping before complex surgery

• There is uncertainty about whether a pelvic mass is an endometrioma or another type of cyst

Both NICE and the International Deep Endometriosis Analysis (IDEA) group recognise that in the hands of a trained specialist, abnormal transvaginal ultrasound performs comparably to MRI for diagnosing deep endometriosis. MRI tends to have longer waiting times and higher cost. The updated NICE guidance now recommends specialist ultrasound as an alternative to MRI in secondary care meaning a good-quality scan can replace the need for MRI in many cases.

What Happens After the Ultrasound?

The scan result shapes the next steps but it does not end the investigation on its own. Here is the typical pathway:

1. Normal scan with ongoing symptoms — NICE is clear: a normal scan does not exclude endometriosis. Your GP or gynaecologist should not dismiss your symptoms. Referral to a gynaecology service remains appropriate.

2. Endometrioma found — referral to a specialist endometriosis service is recommended under the 2024 NICE guideline.

3. Deep infiltrating endometriosis identified — specialist imaging maps the extent of disease, and this information is shared with a multidisciplinary team to plan treatment.

4. Diagnostic laparoscopy considered — if imaging is inconclusive but symptoms are strong, laparoscopy remains the gold standard for confirmation.

At myGynaePlus, the team offers expert-led gynaecological ultrasound as part of a comprehensive approach to women's health, with clear pathways from first scan to specialist care.

Preparing for Your Endometriosis Ultrasound Scan

A few practical things to know before your appointment:

• Transvaginal scan: Empty your bladder before the scan. Wear comfortable clothing. The probe is narrow and covered in a sterile sheath and gel. You are in control — the scan can be stopped at any time.

• Transabdominal scan: Drink around 1 litre of water an hour before and avoid urinating, as a full bladder improves image quality.

• Bowel preparation: If there is a strong history of bowel endometriosis or significant bowel pain, some specialist clinics ask you to take a mild laxative the evening before. Your clinician will advise you specifically.

• Timing: There is no single "best" day in your cycle for the scan, though some clinicians prefer scanning in the first half of the cycle to reduce confounding factors.

  
  

Frequently Asked Questions

1. Can a normal ultrasound rule out endometriosis? 

No. A normal ultrasound does not rule out endometriosis, particularly if symptoms are strong. Superficial endometriosis lesions are too small and flat to appear on any scan. NICE guidance states clearly that clinicians should not exclude endometriosis based on a normal scan result alone.

2. Is a transvaginal ultrasound painful? 

Most women find a transvaginal ultrasound uncomfortable rather than painful. The probe is slim and inserted gently. If you experience pain during the scan, tell the clinician immediately they can stop or adjust the procedure. The examination typically takes around 20 to 30 minutes.

3. Can a pelvic ultrasound detect all types of endometriosis? 

No. A specialist transvaginal ultrasound can detect ovarian endometriomas and deep infiltrating endometriosis (DIE) accurately. Superficial peritoneal endometriosis, the most common type has no detectable mass and cannot be seen on ultrasound or MRI. Laparoscopy remains the only method for identifying it.

4. Why is transvaginal ultrasound better than a standard abdominal scan for endometriosis? 

Because endometriosis mostly affects the area behind the uterus, a transabdominal probe cannot reach those structures clearly. A transvaginal probe sits much closer to the uterus and ovaries, producing sharper, more detailed images of the posterior pelvis where deep disease is most likely to occur.

5. What should I do if my GP says my ultrasound is normal but I still have symptoms?

 Ask for a referral to a gynaecology service. The 2024 NICE guideline (NG73) is explicit: a normal scan does not exclude endometriosis, and referral is still appropriate if your symptoms persist or significantly affect your daily life. You can also seek a private gynaecological review services such as those at myGynaePlus can provide specialist ultrasound and a clinical assessment in one appointment.