An ovarian cyst is a fluid-filled sac that forms on or inside an ovary. Most are harmless, cause no symptoms, and disappear on their own within a few weeks. They’re extremely common: among women over 55 screened with ultrasound, 14% had a simple cyst the first time their ovaries were checked, and about 8% developed a new one each year. In younger, premenopausal women, cysts form even more frequently as a normal part of the menstrual cycle.
How Ovarian Cysts Form
Every month, your ovaries grow small fluid-filled structures called follicles. Each follicle contains an egg. When ovulation happens, the follicle breaks open, releases the egg, and then transforms into a temporary hormone-producing structure. A cyst develops when something in this process doesn’t go as planned, or when other types of tissue in the ovary start growing on their own.
Follicular cysts form when a follicle doesn’t release its egg. Instead of breaking open, it keeps growing, sometimes reaching four inches in diameter. This happens when the hormonal signals that trigger ovulation are off, either from too much of one hormone or not enough of another. These cysts are filled with clear fluid and have a thin wall.
Corpus luteum cysts form after ovulation. Once the egg is released, the leftover follicle normally shrinks. Sometimes it seals back up and fills with fluid or blood instead. These cysts are more active than follicular cysts because they’re producing progesterone, the hormone that prepares the uterus for pregnancy. They also have a rich blood supply, which means they can bleed internally if they get bumped or twisted, causing sudden pain.
Other Types of Ovarian Cysts
Not all cysts come from the normal monthly cycle. Nonfunctional cysts grow from different types of tissue within the ovary and don’t resolve on their own the way functional cysts do.
- Dermoid cysts develop from egg cells and can contain surprising tissues like hair, teeth, and skin. They look distinctive on ultrasound and tend to grow slowly.
- Serous and mucinous cysts are lined with cells that produce fluid. Mucinous cysts in particular can grow quite large because the fluid keeps accumulating.
- Endometriomas form when tissue similar to the uterine lining grows on the ovary. These are sometimes called “chocolate cysts” because they fill with old, dark blood.
Any tissue in the ovary can potentially form a cyst, which is why the variety is so wide. The vast majority of these are benign. Ovarian cancer affects roughly 10.4 per 100,000 women per year, and the lifetime risk of being diagnosed with it is about 1.1%. It’s most commonly diagnosed between ages 55 and 64.
What an Ovarian Cyst Feels Like
Most ovarian cysts produce no symptoms at all. You may have one right now and never know it. They’re frequently discovered by accident during an ultrasound for something else entirely.
When a cyst is large enough to cause symptoms, the most common ones are pelvic pain on one side (either a dull ache or a sharper sensation below the bellybutton), a feeling of fullness or pressure in the lower abdomen, and bloating. The pain may come and go rather than stay constant. Some women also notice feeling full quickly when eating or needing to urinate more often if the cyst is pressing on the bladder.
When a Cyst Becomes an Emergency
Two complications require immediate medical attention: rupture and torsion.
A ruptured cyst spills its contents into the pelvic cavity. This often causes sudden, sharp pain on one side. Most ruptured cysts resolve without intervention, but if the cyst had a significant blood supply (as corpus luteum cysts do), internal bleeding can occur. Signs that a rupture is serious include faintness, dizziness, rapid breathing, cold or clammy skin, or heavy vaginal bleeding.
Ovarian torsion happens when the weight of a cyst causes the ovary to twist on itself, cutting off its blood supply. This produces severe pain, often with nausea and vomiting. Torsion requires surgery to restore blood flow to the ovary before permanent damage occurs. The pain is typically sudden and intense enough that most women go to the emergency room quickly.
How Ovarian Cysts Are Diagnosed
Ultrasound is the primary tool for evaluating ovarian cysts. A transvaginal ultrasound (where a small probe is inserted into the vagina) gives the clearest view of the ovaries and can reveal the cyst’s size, whether it’s filled with clear fluid or has more complex features, and whether it has internal walls or solid areas.
Doctors use specific characteristics to assess risk. A simple cyst, one that’s filled with clear fluid and has smooth, thin walls, is almost always benign. Cysts under 3 centimeters are generally considered normal follicles or corpus luteum structures and don’t need follow-up imaging. Once a cyst exceeds 3 centimeters, it warrants closer evaluation. The 10-centimeter mark is another important threshold: cysts that large carry a slightly higher risk of complications and more often require further workup, sometimes with MRI if the ultrasound findings are unclear.
Features that raise concern include solid areas growing into the cyst cavity, thick internal dividing walls with blood flow through them, and irregular inner surfaces. These don’t automatically mean cancer, but they prompt additional evaluation.
Treatment and What to Expect
The most common approach for a simple, symptom-free cyst is watchful waiting. Your doctor will schedule a follow-up ultrasound, usually in six to eight weeks, to check whether the cyst has shrunk, stayed the same, or grown. Functional cysts frequently disappear on their own within this timeframe without any treatment.
Hormonal birth control can prevent new functional cysts from forming by suppressing ovulation. It won’t shrink a cyst that’s already there, but it reduces the chance of developing additional ones.
Surgery becomes an option when a cyst is large, causing significant symptoms, growing over time, or has features on imaging that need further investigation. Most cyst removals are done laparoscopically, through small incisions, which means shorter recovery times, typically a few days to two weeks of limited activity. In some cases, particularly with very large cysts or concerns about cancer, a larger incision may be necessary. The goal is usually to remove the cyst while preserving as much healthy ovarian tissue as possible.
For women past menopause, cysts are watched more carefully because the ovaries are no longer cycling and producing functional cysts. A new cyst in a postmenopausal woman is more likely to be nonfunctional and may warrant closer monitoring or earlier intervention, though many simple cysts in this age group are still benign.