Endometriosis is the presence of endometrial glands and stroma outside the uterine cavity and the uterine musculature. Usually, a woman or a girl with endometriosis gets terrible period pain and pelvic pain during each menstrual cycle.

The innermost layer of the uterus which is closest to the uterine cavity is called the endometrium. Below it is the muscular myometrium. Along the myometrium, you have branches of the uterine artery called the spiral arteries that go all the way up to the endometrium. These spiral arteries are what help the endometrium grow during each menstrual cycle. It helps deliver hormones and nutrients to the endometrial layer.

The endometrium is the layer that sheds during periods and a new layer will grow. Essentially the endometrium becomes thick once again. However, a woman with a normal reproductive tract can develop endometriosis i.e. the presence of endometrial tissue outside the uterine cavity and uterine musculature. Because it is endometrial tissue, the endometrial tissue outside the uterus will also react to the reproductive hormones. So when you have periods, it will also react.

Let’s take a closer look at what’s going on. The pathophysiology i.e. how and why endometriosis occurs is not fully known but there are a few theories out there. Therefore the theories are that it occurs due to:

1. Retrograde menstruation
2. Vascular lymphatic dissemination
3. Coelomic metaplasia of multipotent cells
4. Impaired immunity

Signs and symptoms

Usually, endometriosis presents in younger women between 20-40 years. The usual symptoms are heavy periods. They can present with chronic fatigue. Infertility i.e. not being able to conceive is a common presentation. Chronic pelvic pain is very common. Severe dysmenorrhea is painful menstruation. They can also have dyspareunia which is deep pain during sexual intercourse and also they can have symptoms of pain during defecation (dyschezia).

Endometriosis should be considered in any female patient with dysmenorrhea who is not responding with non-steroidal anti-inflammatory drugs (NSAIDs). Some women can experience dysuria which is pain during urination if there is ectopic endometrial tissue on the bladder.

There are many differential diagnoses of endometriosis because there are many causes of chronic pelvic pain or painful bleeding. Gynecological causes include adenomyosis (which are endometrial glands found in the myometrium and these glands will also react to hormones during each menstrual cycle); leiomyoma (fibroids); pelvic inflammatory disease which is mainly caused by sexually transmitted infections (STIs) that is a very common cause of chronic pelvic pain. Then you have uterine myoma as well as ovarian cysts both of which are common.

Non-gynecological causes include irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), and interstitial cystitis which is inflammation of the urinary bladder.

Initial investigations for someone presenting with suspected endometriosis include:

1. A full blood count – This is to check for any signs of infection and anemia
2. Serum electrolytes, urea, and creatinine – To check for kidney function
3. An abdominal and transvaginal ultrasound – To see any obvious anatomical changes in the reproductive or non-reproductive organs. Imaging such as an MRI and or CT scan can often help to detect abnormalities around the area and can also sometimes detect ectopic endometrial tissues
4. Laparoscopy – Is actually used to diagnose endometriosis and is the gold standard. It is usually done under general anesthesia. It should be noted that even if a doctor suspects endometriosis it doesn’t mean that the patient has to have a laparoscopy. This is because the management will be the same.

So patients go on medications to see if it helps without having surgery and without confirming the diagnosis of endometriosis.

Mechanism of endometriosis

Although the exact mechanism of endometriosis is unknown, there are some possibly known risk factors including low birth weight, early menarche, short menstrual cycles, late menopause, genetics, and eating lots of red meat. Obesity and certain chemicals increase your chances of developing endometriosis. But there are also protective factors and these include fruits, vegetables, having multiple pregnancies, omega-3 oil, as well as prolonged breastfeeding, and prolonged lactation.

The pituitary gland is an endocrine gland that produces a hormone called luteinizing hormone (LH) in response to gonadotropin-releasing hormone (GnRH) from the hypothalamus. LH induces ovulation. So it targets the ovaries telling them to release an egg at day 14 of the menstrual cycle. So mid-cycle, the egg travels through the fallopian tube and is either fertilized or not by the sperm.

If there is no fertilization, menstruation will occur in two weeks. During this time, before the period, the ovary is actually still producing estrogen and progesterone. But by day 28 of the menstrual cycle, the estrogen and progesterone levels drop. With the drop of estrogen and progesterone, menstruation occurs. The endometrial lining will shed and you get a period.

In endometriosis, because you have endometrial tissue elsewhere outside the uterine cavity, this ectopic endometrial tissue will also react to the drop in hormones and they will also shed. This will cause a really painful period (dysmenorrhea). If the ectopic endometrial tissue is on the bowel or the rectum, it can cause dyschezia.

How does the endometrial tissue actually end up outside the uterine cavity or the myometrium in the first place?

One common theory is that there’s retrograde menstruation where during menstruation, some of the endometrial tissue may have traveled backward (retrograde) along the fallopian tubes into the surrounding peritoneal cavity.

Another theory is the vascular and lymphatic dissemination of the endometrial cells. Here it is essentially thought that the endometrial tissues move via the vasculature (blood vessels) or the lymphatics from the uterus and deposit elsewhere in the peritoneal cavity.

The third theory is based on the coelomic metaplasia of multipotent cells in the peritoneal cavity. Here the ectopic endometrial tissue is thought to come from coelomic epithelial cells that undergo what’s called a metaplastic reaction or metaplasia. Metaplasia is the changing from one normal type of tissue to another normal type of tissue

Basically, the coelomic cells develop into cells of the peritoneum and the surface of the ovary usually. However, the coelomic cells undergo metaplasia and it actually causes these cells to transform into endometrial cells. But these cells are not present in the uterus rather they are present outside the uterus.

Finally, the fourth theory of endometriosis is an impairment of the immune system. The immune system is thought to be dysfunctional in endometriosis. Studies suggest an alteration in the immune system in terms of immune-cell recruitment, cell adhesion, and upregulated inflammatory processes, which can facilitate the implantation and survival of endometriotic lesions

There are three pathological forms of endometriosis.

Endometrioma – This is endometriosis within the ovary. Here an ovarian cyst is formed by ectopic endometrial tissue.

Superficial peritoneal lesion – Typically this type is located on the pelvic organs or the pelvic peritoneum. It has a characteristic powder burn or gunshot lesion appearance.

Deep infiltrative endometriosis – This is a solid endometriosis mass situated greater than 5 mm deep under the peritoneal surface. This type is more likely to require some sort of surgical intervention.

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