Causes

Most ovarian cysts develop as a result of your menstrual cycle (functional cysts). Other types of cysts are much less common.

Functional cysts

Your ovaries normally grow cyst-like structures called follicles each month. Follicles produce the hormones estrogen and progesterone and release an egg when you ovulate.

If a normal monthly follicle keeps growing, it's known as a functional cyst. There are two types of functional cysts:

• Follicular cyst. Around the midpoint of your menstrual cycle, an egg bursts out of its follicle and travels down the fallopian tube. A follicular cyst begins when the follicle doesn't rupture or release its egg, but continues to grow.
• Corpus luteum cyst. When a follicle releases its egg, it begins producing estrogen and progesterone for conception. This follicle is now called the corpus luteum. Sometimes, fluid accumulates inside the follicle, causing the corpus luteum to grow into a cyst.

Functional cysts are usually harmless, rarely cause pain, and often disappear on their own within two or three menstrual cycles.

Other cysts

Types of cysts not related to the normal function of your menstrual cycle include:

• Dermoid cysts. Also called teratomas, these can contain tissue, such as hair, skin or teeth, because they form from embryonic cells. They're rarely cancerous.
• Cystadenomas. These develop on the surface of an ovary and might be filled with a watery or a mucous material.
• Endometriomas. These develop as a result of a condition in which uterine endometrial cells grow outside your uterus (endometriosis). Some of the tissue can attach to your ovary and form a growth.

Dermoid cysts and cystadenomas can become large, causing the ovary to move out of position. This increases the chance of painful twisting of your ovary, called ovarian torsion. Ovarian torsion may also result in decreasing or stopping blood flow to the ovary.