Normal Physiology
During the normal menstrual cycle, the endometrial tissue within the uterus proliferates due to the actions of estrogen and progesterone in preparation for implantation of a fertilized ovum (Huether & McCance, 2019). Hormonal stimulation causes the tissue to grow and glands and blood vessels to branch out into the endometrium. If no ovum is fertilized or implantation is not successful, there is a drop in estrogen and progesterone levels which triggers sloughing of the endometrial tissue and bleeding out of the uterus. After sloughing is complete, estrogen levels rise again, and the cycle starts over with endometrial proliferation (Huether & McCance, 2019).
Pathophysiology
Endometriosis is a disorder characterized by the implantation of endometrial tissue in areas of the body outside of the uterus (Huether & McCance, 2019). The ectopic tissue is typically found in pelvic areas such as the ovaries and pelvic lining and within the abdominal cavity. This tissue is functional, so it proliferates and sheds with stimulation from the normal menstrual hormones (estrogen and progesterone) if blood supply is adequate. This breakdown of tissue outside of the uterus triggers an inflammatory response which may cause fibrosis, scarring, adhesions, and pain (Huether & McCance, 2019).
It is currently unknown what causes the migration of endometrial tissue outside of the uterus which leads to endometriosis (Huether & McCance, 2019). However, one popular theory suggests that it may occur due to a phenomenon known as retrograde menstruation, in which the menstrual blood flow travels back through the fallopian tubes and out into the pelvic cavity. Immune function is also theorized to contribute to the development of endometriosis, with macrophages actually leading to the proliferation of endometrial tissue. Genetic factors may play a role. It is also theorized that endometrial tissue may migrate outside of the uterus during fetal development (Huether & McCance, 2019).
Endometriosis. (2019). Retrieved from https://www.mayoclinic.org/-/media/kcms/gbs/patient-consumer/images/2013/11/15/17/37/ds00289_-my00554_im00303_w7_endometriosisthu_jpg.jpg
Key Criteria for Diagnosis
Typically, only young, premenopausal women are affected. The most common symptoms are pain and infertility (Huether & McCance, 2019). Women may also experience progressive dysmenorrhea, dysuria, painful defecation, painful intercourse, diarrhea (especially following intercourse), and irregular vaginal bleeding. An asymptomatic pelvic mass may develop if the endometrial tissue is implanted within the pelvis. The only way to diagnose endometriosis is through laparoscopic surgery, in which suspect tissue is sampled and identified as endometrial tissue outside of the uterus (Huether & McCance, 2019).