An enlarged ovary is usually not a sign of cancer. The vast majority of enlarged ovaries are caused by benign conditions like functional cysts, and in premenopausal women, the chance that a symptomatic ovarian cyst is malignant is roughly 1 in 1,000. That said, enlargement can occasionally indicate cancer, particularly in postmenopausal women, so understanding what doctors look for helps put an abnormal finding in context.
What Counts as an Enlarged Ovary
Ovary size changes naturally with age. In women under 30, the average ovarian volume is about 6.6 cubic centimeters. That drops to around 4.8 cm³ in the 40s and 2.1 cm³ by the 60s. After menopause, the average is roughly 2.2 cm³, less than half the premenopausal average of 4.9 cm³.
Doctors generally consider an ovary enlarged when it exceeds the upper limits of normal: 20 cm³ for premenopausal women and 10 cm³ for postmenopausal women. If your ultrasound report describes an ovary above these thresholds, it means further evaluation is warranted, not that something is necessarily wrong.
Common Benign Causes
Functional cysts are by far the most frequent reason an ovary looks larger than expected. These form as a normal part of ovulation. Each month, a follicle in the ovary grows, releases an egg, and then shrinks. Sometimes the follicle doesn’t release the egg or doesn’t shrink afterward, creating a fluid-filled cyst. These typically resolve on their own within about 60 days without any treatment and are actually a sign that your ovaries are working normally.
Other benign causes include:
- Endometriomas: Cysts filled with old menstrual blood, linked to endometriosis. They can grow large enough to noticeably enlarge the ovary.
- Dermoid cysts (teratomas): Smooth, rubbery growths that can contain tissue resembling hair, teeth, or skin. They sound alarming but are noncancerous.
- Polycystic ovary syndrome (PCOS): Multiple small cysts develop on one or both ovaries, often causing them to appear enlarged on ultrasound.
Because these conditions are so common, especially in women who are still menstruating, an enlarged ovary found on imaging almost always turns out to be one of these.
When Enlargement Raises Concern
Doctors don’t just look at size. The internal structure of the mass matters far more than how big it is. A simple, fluid-filled cyst under 10 cm is classified as likely benign by the American College of Obstetricians and Gynecologists regardless of how much it enlarges the ovary. What raises red flags is a specific set of features visible on ultrasound:
- Solid components: A mass that is mostly or entirely solid rather than fluid-filled
- Thick internal walls: Separations (septations) thicker than 3 mm inside the cyst
- Papillary projections: Small finger-like growths extending from the cyst wall, especially four or more
- Strong blood flow: A high Doppler signal, meaning the mass has developed its own blood supply
- Free fluid in the abdomen (ascites): Fluid accumulation surrounding the mass
An irregular, solid mass larger than 10 cm with several of these features is treated with much more urgency than a smooth, simple cyst of the same size. The appearance tells the story more than the measurements alone.
Age Changes the Risk Significantly
Your age and menopausal status are among the strongest predictors of whether an ovarian mass is cancerous. In premenopausal women, almost all ovarian masses and cysts are benign. The malignancy rate for a symptomatic cyst rises from about 1 in 1,000 in younger women to roughly 3 in 1,000 by age 50.
After menopause, the calculus shifts. Ovaries that are no longer ovulating shouldn’t be forming new functional cysts, so a new or growing mass in a postmenopausal woman gets more scrutiny. Guidelines from the Society of Radiologists in Ultrasound recommend immediate surgical consideration for indeterminate masses in postmenopausal women, while the same type of mass in a premenopausal woman would typically be monitored with a repeat ultrasound in 6 to 12 weeks.
Symptoms That Add Context
Most ovarian cysts, benign or malignant, cause no symptoms at all in their early stages. When ovarian cancer does produce symptoms, they tend to be vague and persistent rather than sudden or sharp. The pattern that doctors pay attention to includes bloating or abdominal swelling that doesn’t come and go with your cycle, a persistent feeling of pressure or discomfort in the pelvis, and a frequent or urgent need to urinate.
These symptoms overlap heavily with dozens of other conditions, from irritable bowel syndrome to urinary tract issues. What distinguishes them in the context of ovarian cancer is that they’re new, they occur almost daily, and they last for more than a few weeks. An enlarged ovary found alongside these persistent symptoms warrants a more thorough workup than an incidental finding on an unrelated scan.
How Doctors Evaluate an Enlarged Ovary
Transvaginal ultrasound is the first-line imaging tool. It gives a detailed view of the ovary’s size, the consistency of any mass (cystic, solid, or mixed), whether there are internal structures like septations or nodules, and how much blood flow the mass has. This single test provides most of the information needed to classify a mass as likely benign, indeterminate, or suspicious.
Blood tests for a protein called CA-125 are sometimes added, particularly in postmenopausal women. About 80% of ovarian cancers produce elevated levels of this marker. However, CA-125 has well-known limitations. It’s also elevated by endometriosis, menstruation, anovulatory cycles, and general inflammation in the pelvic or abdominal lining. In one large study, 80% of women with elevated CA-125 levels did not have ovarian cancer. When used as a standalone screening tool in asymptomatic women, a positive result corresponds to an actual cancer diagnosis only about 1% of the time. CA-125 is more useful as one piece of a larger puzzle than as a definitive answer on its own.
If ultrasound findings are unclear or malignancy is suspected, MRI or CT imaging can provide additional detail, including whether there’s involvement of nearby lymph nodes or spread to other organs.
What Monitoring Looks Like
When an enlarged ovary appears benign on ultrasound, doctors typically recommend a follow-up scan rather than immediate intervention. Small simple cysts with no blood flow often don’t need any follow-up at all, since they’re likely to resolve within six months on their own.
For masses that look indeterminate, meaning not clearly benign but not suspicious either, the standard approach is a repeat ultrasound in 6 to 12 weeks for premenopausal women. This interval gives functional cysts time to shrink while still catching anything that grows. For masses that remain stable after the first follow-up, many practitioners adopt a schedule of repeat imaging every three months. Research on postmenopausal women with small complex masses found that all five cancers diagnosed during monitoring showed growth on the very first repeat ultrasound, supporting the view that three-month intervals catch concerning changes early.
If a mass grows, develops new solid components, or shows other worrisome changes, surgical removal becomes the next step. In many cases, this can be done with minimally invasive techniques, and the tissue is examined afterward to determine whether it’s benign or malignant. Importantly, ovarian cancer is not diagnosed by biopsy through the skin. The mass is removed intact to avoid potentially spreading cancerous cells.