Most ovarian “cysts” are the result of ovulation, the process of maturing an egg cell within the ovaries. A cyst is simply a fluid-filled sack. It is normal for a woman after puberty to form a cyst, or follicle (the scientific term for an egg cyst) on her ovary every month near her mid-cycle. The follicle harbors an egg for ovulation. These cysts can actually reach sizes of 3.0 cm (1¼ inches). Usually round, simple, and fluid-filled, they are easily visible on ultrasound.

Occasionally, a “cyst” will remain after ovulation (the release of the egg) and sometimes a small amount of bleeding that occurs during ovulation may cause a temporary semi-solid mass appearance on ultrasound. These “hemorrhagic” cysts usually resolve within two to four months, but might cause cramping pain on one side or another. Rarely, this painful cyst may require surgery, such as laparoscopy. These hemorrhagic cysts can be seen on ultrasound during pregnancy at the very site where the egg that resulted in the pregnancy once was, and will generally resolve or “heal” after six to 16 weeks.