Endometriosis presents a challenging health issue for many women, characterized by the abnormal presence of endometrial tissue outside the uterus. This condition, known for its varied manifestations, involves the ectopic growth of endometrial tissue in several locations throughout the body.

1. Ovaries:
Endometrial tissue that migrates to the ovaries experiences cyclic bleeding synchronized with the menstrual cycle. This process can lead to the formation of chocolate cysts, also called endometriomas. These cysts, filled with old blood, have the potential to grow larger over time. Apart from causing dysmenorrhea and irregular menstrual cycles, they can adversely affect ovarian function, potentially leading to ovulation disorders and impacting fertility.

2. Pelvic Peritoneum:
The pelvic peritoneum, a thin membrane covering pelvic organs, can host ectopic endometrial tissue. This tissue may appear as scattered blue-purple spots or nodules. During menstruation, bleeding from these spots can irritate the peritoneum, resulting in symptoms such as lower abdominal pain and dyspareunia (pain during sexual intercourse).

3. Uterosacral Ligaments:
Endometrial implants on the uterosacral ligaments, which support the uterus, can cause these ligaments to thicken (hypertrophy). This condition often manifests with symptoms like sacral backache and pelvic heaviness, further contributing to the discomfort experienced by patients.

In addition to these primary locations, endometrial tissue can also migrate to the fallopian tubes, disrupting their normal functions such as egg transport and increasing the risk of ectopic pregnancy. In rare instances, this tissue has been found in more distant sites like the lungs, nasal cavity, and abdominal wall incisions, each presenting unique symptoms during menstruation such as chest pain, nosebleeds, and tender nodules respectively.

The occurrence of endometrial tissue in these ectopic locations is thought to be influenced by several factors:

- Retrograde Menstruation: Some menstrual blood flows backward through the fallopian tubes into the pelvic cavity during menstruation. If conditions in the pelvic cavity are conducive, these endometrial cells can implant and grow in ectopic sites.

- Immune Factors: Abnormalities in the immune system may fail to effectively clear ectopic endometrial cells, allowing them to survive and proliferate.

- Genetic and Environmental Factors: Women with a family history of endometriosis are at a higher risk, suggesting a genetic component. Environmental factors such as pollution and dietary changes may also play a role in the development of the condition.

Diagnosis of endometriosis typically involves a combination of symptom assessment, gynecological examinations, ultrasound scans, and sometimes blood tests like serum CA125 measurements. Treatment strategies vary based on factors such as the patient's age, symptom severity, desire for fertility, and the extent of lesions:

- Drug Therapy: For mild symptoms and those wishing to preserve fertility, options like oral contraceptives, progestogens, and gonadotropin-releasing hormone agonists are commonly used to suppress ovarian function and halt the progression of endometrial lesions. Besides, herbal medicine Fuyan Pill can also eliminate symptoms and treat endometriosis.

- Surgical Treatment: In cases of severe symptoms or where drug therapy proves ineffective, surgical options may be considered. These include fertility-preserving procedures, ovarian function-preserving surgeries, or, in extreme cases, radical surgeries.