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Ovarian Cyst vs. Ovarian Cancer: Differences on MRI Scans

Medically reviewed by Danielle Leonardo, M.D.
Written by Emily Wagner, M.S.
Posted on October 12, 2023

MRI is a powerful tool used to take detailed pictures of nearly every structure in the body. If you’re experiencing symptoms of ovarian cancer, like pelvic or abdominal pain, your doctor or gynecologist may order imaging tests to take a closer look. Using an MRI, they’ll be able to tell apart ovarian cysts and ovarian cancer — but what are the key differences that distinguish them?

This article will cover how MRI works and when it might be used to diagnose ovarian cysts or ovarian cancer. We’ll also go over the differences your doctor will take note of to make a final diagnosis. If you’re interested in learning more about your MRI results and how your doctor came to a conclusion, be sure to ask at your next appointment.

How Does MRI Work?

MRI uses large, powerful magnets to create a magnetic field around you. The atoms in your body interact with the field, and they all align in the same direction. Then, the MRI scanner sends radio waves through the magnetic field, causing your atoms to move out of position.

When the radio waves are turned off, the atoms go back to their original position. The MRI scanner reads this movement and turns the signals into extremely detailed images of your body’s internal structures. The scanner takes what are known as cross-sectional images, similar to slices of bread in a loaf.

Once the images from your scan are collected, they’re read by a radiologist — a doctor who specializes in diagnosing conditions from imaging tests. They’re trained to recognize changes in your organs and tissues. They’ll discuss the results of your MRI with the doctor who ordered the scan.

Imaging Tests for Pelvic Masses

If you’ve recently been experiencing pelvic pain, abdominal pain, or bloating, your doctor may be concerned that you have an adnexal mass. This is a growth or mass around the uterus, ovaries, and/or fallopian tubes. Their first step will likely be to order some imaging tests to take a closer look at your ovaries, uterus, and nearby structures.

An ultrasound is often the first test used to look for pelvic masses. This imaging technique uses a transducer (wand) to read soundwaves that bounce off your organs, then turns that data into images. If your doctor finds a mass, they’ll order additional tests to find out more about it.

Both ovarian cysts and ovarian cancer can cause this type of mass. Ovarian cysts are fluid-filled or semi-solid sacs that form on the ovaries. These cysts are mostly benign (noncancerous).

Ovarian cysts that form from ovulation as part of a person’s menstrual cycle are known as functional cysts. Abnormal masses that form outside of the normal menstrual cycle are known as complex cysts. They may be classified as tumors, but they’re mostly noncancerous.

Telling ovarian cysts apart from ovarian tumors using just an ultrasound can be difficult, so your doctor may opt to order another test. The most common is CT scans.

Though less commonly used, MRI scans offer an alternative to CT scans for people who want to avoid radiation exposure. Your doctor may prefer to order an MRI if you are pregnant, have concerns about preserving your fertility, or have what appear more likely to be tumors.

Benign Cysts vs. Ovarian Cancer in MRIs

MRI scans create extremely detailed images to help your doctor determine whether you have an ovarian cyst, ovarian cancer, or another similar condition. Radiologists are trained to spot tiny differences in masses and structures to make a final diagnosis.

Benign Cysts in MRIs

Several types of benign cysts can form on the ovaries, each appearing differently in an MRI. For example, functional cysts on an MRI show up as having less fat and more water or fluid.

Types of the cysts include:

  • Cystadenomas
  • Dermoid cysts (teratomas)
  • Endometriomas

Some cysts are a mix of fluid and solid masses — your doctor may be concerned that these are actually ovarian tumors or a sign of metastasis (cancer that has spread from another part of your body). However, you may also have a complex benign cyst, such as a dermoid cyst. These growths contain tissues like teeth, skin, and hair.

A dermoid cysts (teratoma) is a benign cyst that may contain tissues like teeth, skin, and hair. (CC BY-SA 3.0 DEED/Hellerhoff)

There are two types of cystadenomas — serous and mucinous. On MRI scans, serous cysts have thin walls and may have blood inside them. Mucinous cystadenomas tend to be larger than serous ones and contain a gel-like fluid.

Mucinous cystadenomas are benign cysts that contain a gel-like fluid. (CC BY-SA 4.0 DEED/Hellerhoff)

Serous cysts are benign cysts with thin walls. Some are filled with blood. (CC BY 3.0 DEED/A. L. Valentini et al.)

An endometrioma is a mass made of endometrial tissue or the tissue that lines your uterus. An MRI scan helps radiologists tell the difference between this benign cyst and ovarian cancers like clear-cell carcinoma. Endometriomas tend to have more fat tissue, which is easily seen on an MRI.

An endometrioma is a benign cyst made up of the tissue that lines your uterus. They contain higher amounts of fat tissue, which makes them easier to see in MRI scans. (CC BY 3.0 DEED/A. L. Valentini et al.)

Ovarian Cancer in MRIs

Doctors use MRI to determine what tissues a mass is made of and to find out whether it’s cancerous. MRIs can show fluid, solid tissue, fat, and hemorrhage (ruptured blood vessels).

Radiologists look for four key features to diagnose ovarian cancer:

  • Thick septations, which are areas of the tumor divided by membranes
  • Papillary projections, which are areas of tissue that grow and fold over
  • A thick outer wall
  • Necrosis (tissue death)

There are several types of ovarian cancer, but epithelial tumors are the most common. Epithelial tumors form on the epithelial layer (outer layer) of tissue that covers the ovaries. With an MRI scan, radiologists can see that epithelial tumors are solid masses — unlike cysts, which usually contain some fluid.

Clear cell carcinoma is the second most common subtype of epithelial ovarian ovarian cancer. It’s called “clear cell” because the tumors look clear under a microscope. (CC BY 4.0 DEED/Ma, FH., Qiang, JW., Zhang, GF. et al.)

Germ cell tumors make up less than 2 percent of ovarian cancer cases, according to the American Cancer Society. The most common form is dysgerminoma — which often appears as a solid mass with septations and a fibrous cover surrounding the tumor.

These are four MRI images of one dysgerminoma, a form of germ cell tumor. MRI can be used in different ways to see different details. (CC BY 4.0 DEED/Cacioppa, L.M., Crusco, F., Marchetti, F. et al.)

Stromal tumors are less common, accounting for just 1 percent of ovarian cancers, per the American Cancer Society. Unlike epithelial tumors, stromal tumors can take on many different appearances. Some are completely filled with fluid, while others may be solid masses or have hemorrhaging.

Each of these MRI images shows different details of the same stromal tumor. (CC BY 4.0 DEED/Zhao, SH., Li, HM., Qiang, JW. et al.)

If you have questions about what your doctors see on your MRI, you can ask them to point out specific features and explain what they indicate. If you want a second opinion, you can take your scans to another doctor. They may confirm your diagnosis and help you feel more confident about moving forward with treatment, or they may help you avoid unnecessary procedures.

Talk With Others Who Understand

On MyOvarianCancerTeam, the social network for people with ovarian cancer, more than 6,400 members come together to ask questions, give advice, and share their experiences with others who understand life with ovarian cancer.

Have you had an MRI scan for an ovarian cyst or ovarian cancer? What was your experience like? Share your story in the comments below, or start a conversation by posting on your Activities page.

Posted on October 12, 2023
All updates must be accompanied by text or a picture.

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Danielle Leonardo, M.D. is a board-certified specialist in internal medicine and medical oncology from the Philippines and has been practicing medicine since 2014. Learn more about her here
Emily Wagner, M.S. holds a Master of Science in biomedical sciences with a focus in pharmacology. She is passionate about immunology, cancer biology, and molecular biology. Learn more about her here

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