If endometriosis is present, tissue similar to the lining of the uterus grows outside the uterus. This results in tissue islands, also called endometriosis lesions. The problem is that the stray tissue behaves in the same way as its model, the endometrium. Depending on the cycle, it builds up, only to be rejected at the end. This works with the normal endometrium via the vagina during menstrual bleeding. Endometriosis lesions cause inflammation and pain. Due to the fact that tissue remains, adhesions or cysts can also form [1]. The pelvis, ovaries and urinary bladder are particularly frequently affected by endometriosis. In addition, it is possible for endometriosis to occur in the brain [2].

I would like to explore with you today what this means for patients, what it tells us about the development of endometriosis and what treatment can look like.

Where can endometriosis lesions grow?

Doctors distinguish between different forms of endometriosis, depending on where it grows and how it spreads.

• Peritoneal endometriosis: Here, the endometriosis foci are located in the abdominal cavity [2].
• Ovarian endometriosis: The stray tissue affects the ovary [2].
• Adenomyosis uteri: In this case, stomatal cells (nourish and support the organ) and endometrial glands are present in the uterine muscles. These are otherwise found only in the mucosa. As a result, enlargement of the uterus may occur [2, 3].
• Deep infiltrating endometriosis: In this form, the endometriosis lesions overcome the surface and grow at least 0.5 cm into nearby tissues and organs [4].
• Endometriosis extragenitalis: Here, the endometriosis tissue grows outside the genital tract. Thus, the mucosal deposits may also occur in the intestine, diaphragm, urinary bladder, and lungs. In rare cases, endometriosis also affects the brain [2].

So today’s article is about the form endometriosis extragenitalis.

Endometriosis lesions in the brain: rare but possible

When it comes to gynecological diseases, endometriosis takes second place right after fibroids. It is believed that endometriosis affects 5-10% of all women of childbearing age [5]. However, endometriosis lesions in the brain are a real rarity. Only rarely does the tissue find its way to the command center in the head. There are no exact figures on how many patients this is the case for. There is also not much knowledge about the possible complaints, since only individual cases are ever reported. In such reports, endometriosis has been noted for neurological symptoms, i.e. symptoms affecting the nervous system. These include headaches, seizures, or loss of consciousness [6].

However, since these symptoms are very nonspecific, meaning that they can have many other and more likely causes, the diagnosis is virtually a diagnosis of exclusion. So if no other explanation fits, the physician should keep endometriosis in mind.

Above all, headaches can occur cycle-dependently even without endometriosis.

Finally, the typical endometriosis symptoms can also be in the foreground.

These include [5]:

• Abdominal pain
• Feeling of fullness
• Nausea
• Menstrual irregularities
• Infertility
• Back pain
• Pain during sexual intercourse

Good to know.

Endometriosis is often diagnosed when a woman is in her childbearing years, especially between the ages of 20 and 40. This can be attributed to the fact that hormonal control of the menstrual cycle has an impact on endometriosis lesions and therefore symptoms. However, only 65% of all patients report symptoms [5]. Endometriosis can therefore remain undetected for a long time.

How do endometriosis lesions get into the brain?

It is a long way from the uterus to the brain. Therefore, the question of how endometriosis lesions make it to the brain is justified. At this point, different theories take hold. Let’s discover together what assumptions there are about endometriosis development.

1. Retrograde menstruation: Since menstrual bleeding does not occur exclusively via the vagina, as is often assumed, but also enters the abdominal cavity via the fallopian tubes, the cells of the endometrium could settle there. Sounds logical at first, but is not an explanation for why not all women develop endometriosis during menstruation [5, 7].
2. Altered epithelial cells: Another theory is that epithelial cells (epithelium = demarcating tissue or covering tissue) on the surface of the peritoneum change to support development of endometriosis. Since both epithelial cells and endometriosis cells have the same origin, this would be conceivable in principle [6].
   Metaplasia of embryonic remnants: this is where it gets a little complicated. You may have heard of the Müller duct. This is an embryonic genital anlage. It is the same in both sexes. It is responsible for the formation of the vagina, uterus and fallopian tubes in women [5]. Researchers can imagine that in endometriosis there is a transformation of the embryonic remains of the Müller ducts [5, 6].
   Abnormalities in the immune system: In endometriosis, the immune system also repeatedly comes into focus. It is possible that a misdirected immune cell response could promote endometriosis [6].
3. Transport by the blood and lymph: Both blood and lymph have important functions in the body. The lymphatic system performs a cleansing function, while the blood transports nutrients and oxygen, as well as supporting the immune system. Fluids are constantly circulating in the organism. One theory is that endometriosis cells can be distributed in the body through the blood vascular system or lymphatic system [6].

In the case of endometriosis lesions in the brain, the theory that endometriosis cells can be distributed via the lymphatic and blood vascular systems, or form in situ, seems most likely. However, substantial research is still needed in this area.

Endometriosis in the brain: diagnostics

There are various ways of detecting endometriosis. To begin with, a detailed medical history (doctor-patient discussion) is very important. In this way, existing complaints can be collected and the physician obtains an overview of the quality of life. With a vaginal ultrasound device, endometriosis lesions can be made visible in some places, such as between the intestine and the vagina (rectovaginal), and with trained examiners. This is not possible in the brain because the bone strongly reflects the ultrasound waves. If the stray tissue is suspected to be in the intestine, ultrasound examination via the rectum is possible. During a laparoscopy, endometriosis lesions can be examined more closely. This also gives the surgeon an impression of the extent to which the foci have spread. If tissue is removed during the laparoscopy, it can later be examined in the laboratory and thus the diagnosis of endometriosis can be confirmed [5].

However, all these measures do not help to detect endometriosis foci in the brain. They only serve to assess whether the tissue has settled outside the uterus in the typical locations.
An MRI (magnetic resonance imaging) can reliably reveal endometriosis lesions [9]. It is also possible to detect the mucosal islands in the brain or endometriosis in the lungs. Your physician will discuss with you which diagnostic options are indicated for you.

How are endometriosis lesions in the brain treated?

The brain is a very complex and sensitive organ. Therefore, surgical interventions are only performed here if they are promising and absolutely necessary. If endometriosis lesions have settled in the brain, the physician decides on the further procedure. Often, an initial attempt is made to treat the endometriosis with medication. For this purpose, the German Society for Gynecology and Obstetrics suggests a suitable progestogen such as Dienogest in its guideline [2]. This is a synthetically produced corpus luteum hormone that acts in a similar way to the body’s own progesterone. In the body, the substance is supposed to counteract an excess of estrogen, which is often present in endometriosis. In this way, the symptoms and prognosis for patients can be improved.

Good to know.

Endometriosis is related to hormones. Learn more about the topic in our article “Estrogen and endometriosis: exciting connections”.

Short and to the point

In endometriosis, there are islands of mucous membrane outside the uterus, also called endometriosis lesions. These consist of tissue that resembles the lining of the uterus. In patients, the unwanted growth can lead to symptoms such as abdominal pain, infertility and menstrual disorders.

Often the growths in the pelvis,

on the ovaries or in the urinary bladderobserved. However, they can also occur in the lungs or even the brain. Admittedly, endometriosis in the brain is a rarity. That is why research is still in its infancy. How endometriosis cells manage to sneak into the command center in the brain is still unclear. Among other things, there is a theory that endometriosis cells spread through the blood and lymphatic system. To visualize the changes, an imaging procedure such as an MRI is particularly suitable. For therapy, proven methods such as drug treatment with progesterone can be considered.