Adenomyosis is a uterine disorder. The uterus has three layers: the endometrium, the myometrium and the perimetrium (also called the serosa). The inner layer is the endometrium. This layer responds to hormonal stimulation and thickens each month. The endometrium is the layer that is shed each month in the form of a menstrual period. The outer layer is called the myometrium and is the muscular layer. The myometrium contracts to expel the blood from the uterus which can be felt in the form of menstrual cramping. This muscular layer also contracts during childbirth. The perimetrium is the outermost layer of the uterus. In a normal uterus, these layers are distinct and separate from each other.
In adenomyosis, however, the endometrial layer invades the myometrium.
Adenomyosis is defined as the invasion of endometrial tissue ≥2.5 mm in depth into the myometrium along with smooth muscle hyperplasia. In addition, the uterus is enlarged and globular, and the junctional zone width (see below) is ≥12 mm. This results in bleeding within the muscle along with excessive menstrual bleeding, bloating, severe pain and other issues (see Symptoms).
The invasion of the endometrium into the myometrium can lead to several different types of adenomyosis:
- Diffuse – small endometrial implants are found throughout the uterine wall. Diffuse adenomyosis used to be very difficult to pick up, but advances in imaging have led to the ability to pick up this disorder by ultrasound and/or MRI. During a pelvic exam, the doctor might identify the uterus as being soft, tender or enlarged. Also the uterus becomes heavier with more diffuse involvement. The patient may become extremely bloated due to the enlarged and heavy uterus.
- Focal – a large area of adenomyosis in one area of the uterine muscle. This is also referred to as an adenomyoma. An adenomyoma can be felt as a mass during a pelvic exam and can be more easily picked up on radiological exams. In fact, these adenomyomas have been misdiagnosed as fibroids (leiomyomas) in the past.
- Cystic – A very rare form of adenomyosis called juvenile cystic adenomyosis affects young women less than 30 years old and involve cysts found in the myometrium that contain hemorrhagic fluid.
No one really knows for sure what causes adenomyosis. Many theories have been offered, but none have been proven. However, studies are ongoing, and some interesting facts have come forth regarding this disorder. The two main theories include:
- There is a disruption of the boundary between the endometrium and the myometrium. This theory makes sense since many women with adenomyosis have had surgical procedures that interrupt the endometrial-myometrial boundary (also known as the junctional zone) including C-sections and D&Cs. However, there are also known cases of adenomyosis in teenagers and in women who have NOT had prior uterine surgery. This emphasizes the need for additional research into this disorder.
- There are pluripotent Müllerian stem cells that undergo altered differentiation.
One of the most useful findings has involved a part of the uterus called the junctional zone. As described previously, the uterus is made up of the endometrial layer which is shed every month in the form of a menstrual period and the myometrial layer which is the muscular layer. The innermost layer of the myometrium is called the junctional zone, or JZ. Studies have shown that the JZ in women who suffer from adenomyosis tends to be thicker than in women who do not suffer from the disorder. In general, a JZ thickness of less than 8 mm means that adenomyosis is unlikely whereas a JZ thickness of greater than 12 mm indicates that adenomyosis is highly likely. This finding, which can be picked up on MRI, is a huge step in being able to diagnose adenomyosis prior to hysterectomy.
Studies have indicated that this disorder involves an impared response to sex hormones. Also, women who suffer from adenomyosis tend to have a higher level of the COX-2 prostaglandin present in their bodies. This would explain why NSAIDs such as Advil or Aleve can give some relief in some cases.
On a genetic level, some progress has also been made. Studies have indicated that alterations in the vascular endothelial growth factor gene (VEGF) may play a role in the development of adenomyosis. The gene for VEGF is located on chromosome 6 at p16. In addition, a deletion on the long arm of chromosome 7 has been reported in both adenomyosis and fibroids.
The following are some risk factors for the development of adenomyosis:
- Prior uterine surgery
- Increased estrogen exposure
- Poor diet
- Poor liver health
- Immune system dysfunction or autoimmune disease
- Antidepressant use
Fibroids, polyps and endometriosis are commonly found in patients with adenomyosis. It is important to know that a hysterectomy can cure adenomyosis but it CANNOT cure endometriosis. If a woman with adenomyosis has a hysterectomy but continues to have pain after surgery, she may also have endometriosis.