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Adenomyosis vs Endometriosis: What’s the Difference?

Adenomyosis and endometriosis are at first sight very similar, but they’re actually different conditions. We’ve rounded up the most popular questions about them for Dr. Christian Becker — Associate Professor and Co-Director of the Oxford Endometriosis CaRe Centre — to answer.

What are the similarities and differences between adenomyosis and endometriosis?

People used to believe that adenomyosis was a form of endometriosis and vice versa. Presently, particularly deep endometriosis is still sometimes referred to as adenomyosis externa. One thing the conditions have in common is that there’s still much to learn about both of them. 

“At the moment, we know very little about endometriosis, but we know even less about adenomyosis because it’s even more difficult to get to. It’s a diagnosis that can only be made with ultrasound or MRI. And if you find it, you usually treat it with the Mirena IUD or an oral contraceptive pill.” 

Endometriosis, on the other hand, can be detected (or ruled out) with laparoscopy.

There are some unspecific signs for adenomyosis during laparoscopy, but they’re less obvious than endometriotic lesions. Although ultrasound and MRI detection are very good, the only way to be absolutely certain of adenomyosis is under the microscope, usually after a hysterectomy.

What causes adenomyosis isn’t clear, but, many experts believe that endometriosis is often caused by implantation of endometrial cells from menstrual blood in the event that it flows upwards through the uterine tubes into the abdomen — a process called retrograde menstruation.

So what’s the main difference? 

“I think they are two different conditions with similar symptoms. Adenomyosis is the presence of endometrium outside of the uterine cavity but still contained within the uterus, whereas endometriosis is defined as the presence of this tissue outside the uterus,” Dr. Becker explains. 

What causes adenomyosis isn’t clear, but many experts believe that endometriosis is often caused by implantation of endometrial cells from menstrual blood in the event that it flows upwards through the uterine tubes into the abdomen —  a process called retrograde menstruation. 

“However, even that is very theoretical, and I haven’t seen any models that fully support this. So I think what causes these conditions is a very difficult question to answer,” Dr. Becker says.

Does treatment differ for endometriosis and adenomyosis?

Although the recommended treatments for the two conditions are the same, they’re usually prescribed in a different order. Most doctors would recommend the Mirena IUD to people with adenomyosis first and try birth control pills second. 

For people with pelvic pain and heavy or irregular periods who don’t show any signs of adenomyosis on an ultrasound or MRI, doctors are more likely to try birth control pills before recommending the IUD.

Becker - difference endo and adeno

But Dr. Becker says it’s not necessarily important which you try first: “You could argue that both of these treatments work and, therefore, it doesn’t really matter so much. 

“It may matter from a fertility aspect, because there is increasing data that adenomyosis also has an impact on implantation and fertility. Maybe from that perspective, it matters. At the same time, hormonal therapy is not the right approach in this situation because it acts as a contraceptive.”

For people with adenomyosis who are older and have had children or don’t want to have children, doctors may be more likely to bring up the option of hysterectomy, which is surgical removal of the uterus. 

But if adenomyosis isn’t suspected, it’s more likely that they have endometriosis, in which case a hysterectomy might not improve their pain. According to Dr. Becker: “Obviously the periods would cease but not necessarily the pain. Therefore, one would have to have a very detailed discussion about the pros and cons of the procedure and manage the patient’s expectations.”

How are adenomyosis and endometriosis diagnosed?

Dr. Becker believes that medicine is getting better at identifying both adenomyosis and endometriosis thanks to improving ultrasound technologies and experienced radiologists and sonographers: 

“I think it’s clear that you can identify ovarian cysts very easily. But I think we’re getting much better at identifying deep endometriosis and deep endometriosis nodules, not only because you can see it better, but also because the training is better for the people doing it. Plus, the machines have better sensitivity now, or better specificity in this case.” 

Non-invasive means of detecting or ruling out endometriosis are still urgently needed particularly as there are approximately 190 million women affected by the disease worldwide.

Unfortunately, imaging technologies haven’t yet evolved to a point that they can sufficiently detect or rule out peritoneal endometriosis (endometriosis in the pelvic cavity). But if the endometriosis has caused scarring and adhesions, a transvaginal ultrasound can be used to see if any internal organs are stuck together. It’s not a guarantee that these adhesions are endometriosis, though — they can also be caused by other conditions or prior surgery. 

When it comes to the best way to diagnose endometriosis, Dr. Becker says, “Laparoscopies are still considered the gold standard for the identification of endometriosis. However, they are invasive procedures associated with some risks to the patient. That’s why non-invasive means of detecting or ruling out endometriosis are still urgently needed to make sure the approximately 190 million people worldwide who are affected by endometriosis receive the treatment they need.”