Your pathology report for mature cystic teratoma of the ovary

By Jason Wasserman MD PhD FRCPC
August 25, 2025

A mature cystic teratoma is a noncancerous tumour of the ovary. It is made up of mature (fully developed) tissues that come from two or three of the body’s germ layers. Germ layers are the basic building blocks that form all the organs in the body.

The three germ layers are:

  • Ectoderm – Contains tissues like skin, hair, and nerves

  • Mesoderm – Contains tissues like bone, cartilage, and muscle

  • Endoderm – Contain tissues like the lining of the lungs, thyroid, or intestines

Because the tumour contains mature tissues, it may look very different from normal ovarian tissue. For example, it may contain hair, skin, teeth, or fat. Mature cystic teratoma is also known as a dermoid cyst, although this name is no longer preferred.

Who gets a mature cystic teratoma?

Mature cystic teratomas are most often seen in women of reproductive age, although they can occur at any age. They are among the most common ovarian tumours, making up about 20% of all ovarian neoplasms. About 10% of women will develop them in both ovaries.

What are the symptoms of a mature cystic teratoma?

Many women with a mature cystic teratoma have no symptoms, and the tumour may be found by chance during imaging or surgery.

When symptoms do occur, they often include:

  • Abdominal or pelvic pain.

  • A noticeable lump or mass in the lower abdomen.

  • Pressure or discomfort due to the size of the tumour.

Rarely, mature cystic teratomas can be associated with anti-NMDAR encephalitis, a condition where the immune system attacks the brain and causes symptoms such as confusion, seizures, or unusual movements.

What causes a mature cystic teratoma?

The exact cause is not known. The most widely accepted theory is called the parthenogenetic theory, which suggests that the tumour develops from a germ cell in the ovary. Germ cells are special cells that normally develop into eggs.

How is this diagnosis made?

The diagnosis of a mature teratoma is usually made after the tumour has been removed and examined by a pathologist. In many cases, a mature teratoma is first suspected when imaging studies such as an ultrasound, CT scan, or MRI show a mass in the ovary that contains fat, hair, or calcifications. These findings are common in mature teratomas and help distinguish them from other types of ovarian tumours.

What does a mature cystic teratoma look like without a microscope?

When examined by a pathologist without a microscope, most mature cystic teratomas look like cysts (fluid-filled sacs). They are often between 5 and 10 cm in size. Inside, they may contain thick oily fluid, hair, teeth, or cartilage. A solid nodule called a Rokitansky protuberance is often found on the inside of the cyst wall and may contain hair or teeth. Less commonly, the tumour is mostly solid.

What does a mature cystic teratoma look like under the microscope?

When viewed under the microscope, mature cystic teratomas are made up of different types of mature tissue:

  • Ectodermal tissue such as skin, hair follicles, sweat glands, or nervous tissue like brain or spinal cord cells.

  • Mesodermal tissue such as fat, cartilage, bone, or muscle.

  • Endodermal tissue such as thyroid, lung, or intestinal lining. A tumour made up mostly of thyroid tissue is called a struma ovarii.

Because immature teratomas can sometimes develop from mature teratomas, pathologists carefully examine all areas of the tumour to make sure there are no immature tissues present. This is important because an immature teratoma requires different treatment and follow-up than a mature teratoma.

Can a mature cystic teratoma become cancerous?

In the vast majority of cases, mature cystic teratomas are completely benign and do not spread. Very rarely, another type of cancer may arise within a teratoma. This is called somatic malignant transformation. For example, a squamous cell carcinoma or thyroid-type cancer can rarely develop from tissues inside the teratoma.

Another rare complication is gliomatosis peritonei, which occurs when small bits of nervous tissue are found outside the ovary. Fortunately, this condition does not usually worsen the prognosis.

What is the difference between a mature teratoma and an immature teratoma?

Both mature teratomas and immature teratomas develop from germ cells in the ovary. The difference between the two lies in the type of tissue found inside the tumour.

A mature teratoma is made up of fully developed (mature) tissues, such as skin, hair, fat, bone, or thyroid tissue. Because the tissues are mature, the tumour is considered benign and does not spread or behave aggressively.

An immature teratoma contains immature (not fully developed) tissues, most often immature neural tissue that resembles developing brain cells. The presence of immature tissue makes the tumour malignant, meaning it has the potential to spread to other parts of the body. Immature teratomas are usually treated more aggressively than mature teratomas, and the stage and grade of the tumour are important in predicting the outcome.

What is the prognosis for a mature cystic teratoma?

The prognosis is excellent. Mature cystic teratomas are cured by surgery and almost never come back once they are completely removed. Even when rare microscopic immature tissues are found, the outcome is still very good.

Questions to ask your doctor

  • Was my tumour completely removed?

  • Were both ovaries examined, and if so, were both involved?

  • Did my tumour show any unusual features such as immature tissue or evidence of cancerous transformation?

  • How often should I have follow-up visits or imaging after surgery?

  • Do I need to be concerned about the risk of developing another teratoma in the other ovary?

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