Endometriosis, often referred to as a 'chocolate cyst,' is a condition whose precise etiology remains unknown. The most widely accepted theory suggests retrograde menstruation as the primary cause. During menstruation, some endometrial tissue, instead of exiting the body, flows backward through the fallopian tubes into the pelvic cavity and other regions. Endometriosis occurs when these displaced tissues implant and grow outside the uterus.

This pathological growth can manifest with symptoms such as severe lower abdominal pain during menstruation, frequently accompanied by heavy vaginal bleeding.

Several factors are thought to contribute to the development of endometriosis:
* Retrograde menstruation
* Genetic predisposition
* Immune system dysfunction
* Estrogen hormone imbalances
* Surgical interventions, such as C-sections or hysterectomies.