Endometriosis is a debilitating condition that causes intense pelvic pain, infertility, chronic fatigue, and pain during urination, bowel movements, and sex. It can have multiple causes with many similar symptoms to other gynecological and abdominal conditions, which makes its diagnosis difficult.
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The gold standard¹ for diagnosing endometriosis is laparoscopy (a minor surgery through “keyholes”). This allows for actual visualization of the endometriotic lesions, their locations, and how extensive they are. What is also beneficial is the therapeutic nature of this surgery: the lesions can be removed at the time of surgery, resulting in instant relief from the symptoms. The surgery has been traditionally exploratory, meaning that the surgery was largely unplanned beforehand as the surgeon didn’t have an accurate picture of the status of the disease and would gain that information from the surgery.
However, medical imaging such as transvaginal ultrasound (TVU) and magnetic resonance imaging (MRI) have drastically improved the preoperative picture, allowing for more advanced surgical planning.
Ultrasound uses high-frequency sound waves and their “echoes” to construct images through a transducer or receiver. It is an incredibly accurate imaging method that eliminates the need to be still for long periods as with an MRI and does not use radiation as with computed tomography (CT). It is also far cheaper than other methods and more readily available. For these reasons, it has become a first-line imaging process for females with pelvic pain or suspected problems. Sometimes, ultrasound scans need to be followed up with an MRI or CT to better quantify the problems found, but it remains a fantastic first-line imaging option².
In recent decades, the transvaginal ultrasound probe (TVU) was developed, which allows for even more accuracy and usefulness of a pelvic ultrasound scan. It is a wand that is carefully and gently inserted about two to three inches into the vagina, where it can be close to your pelvic organs. Despite seeming like an invasive test, you will be with a trained professional, and the insertion is gentle and never without your full consent. In many cases, you can do the insertion yourself, at which point the operator can take hold of the wand and continue the exam.
TVU has a high specificity and sensitivity rate (for ovarian endometriosis, it is well over 90%³ for both), which means it is considered highly accurate in diagnosing endometriosis. Given this, TVU is operator-dependent, unlike MRI, so it’s only performed by trained sonographers who have significant experience in this area.
If you do have endometriosis, there will be a number of signs that will be present on the ultrasound scan. This will be most obvious if it is ovarian endometriosis, which presents with large cyst-like structures in the ovaries termed “chocolate cysts.”⁴
While these “chocolate cysts'' or endometriomas may be some of the most visible signs on the ultrasound, the operator will know to also look for other signs. The International Deep Endometriosis Analysis Consensus Group (IDEA) has developed a standardized ultrasound protocol⁵ for endometriosis. This involves a series of steps and their possible findings, which include both static (still) and dynamic (moving in real-time) imaging:
Uterus and adnexa
The first step⁶ is to evaluate the uterus for adenomyosis (where endometrial cells from the inner uterine lining invade the muscle layer of the uterus) and the ovaries for endometriomas. Adenomyosis appears as striations (stripes) that almost look like Venetian blinds in the muscle layer. Endometriomas will appear as a cyst or oval structure with defined borders and no internal products or structures. If the sonographer detects endometriomas in the ovary, it is very important they continue with the second part of the protocol as endometriomas are a reliable marker of the severity of endometriosis. Up to 50% of the severe form of endometriosis, known as deep infiltrating endometriosis (DIE), will have associated endometriomas.
This part of the exam also looks at abnormalities associated with the fallopian tubes, which can be present in up to 30%⁶ of cases.
Deep infiltrating endometriosis (DIE)
DIE is the most severe form of endometriosis and is deep and extensive. It can be found throughout the pelvic cavity (and sometimes even further outside). Here, the sonographer needs to be thorough, ensuring they image the whole of the anterior (front) and posterior (back) compartments containing the bladder and bowel. DIE will appear as low-intensity linear or round protrusions⁶ with smooth or wavy borders and show little to no internal blood supply.
This is a dynamic study where pressure is applied to the wand to try and cause the internal organs to “slide” around each other. Specifically, the sonographer is trying to get the uterus to move freely, independent of the bowel. If this fails, it is often because there is “obliteration of the POD”⁶ (Pouch of Douglas), which means the front part of the rectum is fused to the back part of the cervix. This indicates the presence of adhesions (where structures are connected incorrectly through inflammatory scar tissue)— a mark of endometriosis.
These refer to things that are patient-specific that the sonographer can obtain in real-time. So, for example, they can use site-specific tenderness (pressing on the sore part) and image the internal anatomy beneath. They can also press on the abdomen with their free hand while simultaneously moving the wand so that information is obtained about the motility of the organs in relation to each other. They can also talk to the patient and gain more information about what aggravates their symptoms. It has been shown⁶ that shallow endometriosis and adhesions are more likely to exist if the sonographer detects positive soft markers.
TVU is undoubtedly useful in diagnosing endometriosis, but it is not 100% accurate as a standalone test. It should be used in conjunction with a physical exam and detailed patient history. Often this still simply indicates a strong likelihood of extensive disease and facilitates surgical planning, with the gold standard of diagnosis being laparoscopic surgery. Here are some tests that can complement an ultrasound scan:
Magnetic resonance imaging (MRI)
This is useful as a second-tier test to TVU⁷ as it provides a detailed map of the extent of DIE and allows for the most accurate surgical planning. It gives far more detail of DIE lesions than what is possible through a physical exam or TVU. However, definitive diagnosis is still only obtained through laparoscopic surgery where cell types can be confirmed.
Surgery remains the gold standard for diagnosing and staging endometriosis. It has the added benefit of being therapeutic because lesions can often be removed at the time of surgery, improving the patient’s symptoms almost instantly and their associated infertility over time (between 20-60%⁸ improvement in spontaneous pregnancy).
Combined oral contraceptives (COCs)
Due to the hormone-dependent nature of endometriosis, some studies⁹ have reported evidence to show women with endometriosis experience relief from their period pain (dysmenorrhoea) when treated with COCs. Although not definitive, this can help point specialists in the direction of a hormone-dependent issue, which may highlight the need for diagnostic imaging.
Ultrasound is the usual first step in imaging for investigating any female pelvic pain, and this has been supported by an endeavor of the American Institute of Ultrasound in Medicine called “Ultrasound First.”⁵ This is because, from analysis of the literature, ultrasound has been shown to be just as good as CT or MRI for problems causing pelvic pain and often removes the need for further testing.
Here are some pros and cons of using ultrasound for endometriosis diagnosis.
Dynamic, real-time imaging possible
High sensitivity and specificity
Comparable to other imaging modalities
Does not use radiation
Suitable for people with surgical metallic implants or fragments (whereas MRI is not)
Only suitable in conjunction with a physical exam
Can be painful due to aggravation of tender points
Can feel invasive due to transvaginal probe
Sometimes requires a full bladder which can be difficult to achieve
Is not as helpful in detecting early-stage disease
Ultrasound is a very effective and readily available test for diagnosing moderate to severe endometriosis and planning the surgery to confirm and remove it. It is relatively non-invasive, quick, does not use radiation, and provides good information about the extent of the disease.
If you suffer from debilitating pelvic pain and need some answers, it may be worth asking your doctor for an ultrasound. It is easy, and it may well help you get the diagnosis you need.
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