We do not know why these cells seed in some women and not in others. This theory is called retrograde menstruation. Early implants look like spots or pimples sprinkled on the pelvic surfaces. The implants may remain unchanged, become scar tissue, or disappear over a period of months. In most women endometriosis grows slowly and can remain stable for years.
Endometriosis can form benign cysts on the ovaries called endometriomas.
These may be smaller than a pea, or larger than a grapefruit. A woman may suddenly feel pain when a large endometrioma bleeds or bursts. The spilled fluid may cause further irritation and the development of scar tissue. In severe cases, the web-like scar tissue, adhesions, may bind the uterus, tubes, ovaries and nearby intestines together. Endometriosis can grow into the walls of the intestine or into the tissue that separates the rectum from the vagina.