What Is a Teratoma? Types, Causes, Symptoms, and More

Medically Reviewed by Jabeen Begum, MD on December 08, 2023
6 min read

Teratomas are rare tumors that contain different types of tissues such as bone, teeth, muscle, and hair.

A teratoma may be cancerous or benign (noncancerous), depending on its structure. Most are benign. These can grow quickly, but they don't spread to other parts of the body. Cancerous (malignant) ones do spread.

How common are teratomas?

While all teratomas are considered rare, some are more common than others. Sacrococcygeal teratomas, which develop in the tailbone area, are diagnosed in about 1 in every 40,000 newborns. But fetiform teratomas affect only about 1 out of every 500,000 people.

There are two main types of teratoma tumors:

Immature teratomas

These are made up of nerve tissue that never matured. They have a high chance of being cancerous, and they can quickly spread throughout your body. They're most often found in children.

Mature teratomas

These are more likely to be benign and usually appear during your reproductive years. Unlike the immature type, they contain fully developed tissues. They fall into one of three categories:

  • Solid: Made of tissue but not enclosed
  • Cystic: Contained by a sac
  • Mixed: Having both cystic and solid parts

Mature teratomas are often found in the ovaries and are more likely to happen before menopause. The longer a teratoma remains inside your body, the more likely it is to become cancerous.

Fetiform teratoma is the rarest type of teratoma. It looks like a malformed fetus without an amniotic sac or a placenta. It's sometimes confused with a condition called fetus in fetu, in which a twin that's unable to develop gets enveloped by its surviving sibling while in the womb. Over 90% of fetiform teratomas are found in children younger than 18 months.

Teratomas can be found anywhere on the body, but they more often happen in certain locations:

  • Sacrococcygeal teratomas develop before birth on the tailbone. They're usually benign. They're the most common type of teratomas in children.
  • Ovarian teratomas form later in life in an ovary and are most common type in women (and those identified as female at birth). These are also usually noncancerous.
  • Testicular teratomas are found in a testicle. You might hear them called testicle teratomas, and they're the most common type to affect men and those identified as male at birth. When they develop during childhood, they're usually benign. But when found in adulthood, about half of them are cancerous. A testicular teratoma that's cancerous is called a teratocarcinoma.

Fetiform teratomas are often found in the ovaries but can grow in other parts of the body as well.

A mature cystic teratoma that forms on an ovary is sometimes described as a dermoid cyst or dermoid tumor. Dermoid means "like skin."

But in general, "dermoid cyst" refers to a simpler type of skin growth that most often affects the head, face, neck, and upper chest. These slow-growing, noncancerous cysts are filled with old skin cells and oil.

It's not clear exactly what causes teratomas to form.

These tumors form in your body's germ cells, which are what's called undifferentiated. This means they can develop into any type of cell—from egg and sperm to hair cells.

As a baby develops, their germ cells start moving to various places in the body to become different types of cells. That's why teratomas contain different tissues and body components like:

  • Hair
  • Teeth
  • Fat
  • Skin
  • Muscle

Some even contain parts of organs like the liver or lungs.

Risk factors for teratomas

The risk factors vary, depending on the type and location of tumor.

Being born female puts you at a higher risk of sacrococcygeal teratomas. They're four times more likely to affect those with female anatomy. But they're more likely to be cancerous in those who have male anatomy.

Things that may increase your risk of a testicular teratoma include:

  • Low birth weight
  • Birth to a mother older than 35 years
  • An undescended testicle
  • A condition called hypospadias, in which your urethra opening is somewhere other than the tip of your penis
  • Jaundice, a condition that happens when a baby has too much of a substance called bilirubin in their blood

Among the possible risk factors for mature ovarian teratomas are:

  • Infertility
  • Periods that aren't regular
  • Starting your period later in adolescence
  • Alcohol misuse

A mature ovarian teratoma is more likely to become cancerous if you:

  • Are past menopause
  • Have a large tumor
  • Have high levels of a protein called cancer antigen 125 in your blood

In general, you may notice these symptoms if you have a teratoma:

  • Swelling
  • Bleeding
  • Pain

You may have other symptoms, depending on what kind you have. Some can be visible, such as those on the tailbone. Others aren't, so see a doctor if you're having the symptoms above. With a prompt diagnosis, treatment is more likely to be successful.‌

Sometimes, a teratoma doesn't cause any symptoms at all.

Symptoms of sacrococcygeal (tailbone) teratomas

These are sometimes visible but sometimes grow inside the body where you can't see them.

Other symptoms may include:

  • Leg weakness because the tumor is in the lower back
  • Swelling in the groin
  • Pain when you pee
  • Belly pain
  • Constipation

Often, a doctor finds one before birth during an ultrasound. The tumor can make the uterus grow larger than it should be.

Symptoms of testicular teratomas

You may see a lump or lumps in your testicles. You may also have swelling in the area. Although you can get one at any age, a testicular teratoma usually affects people in their 20s.‌

Symptoms of ovarian teratomas

The main symptom is pain in your belly or pelvic area. As ovarian teratomas grow larger, they can put a lot of pressure on your ovary, causing it to twist. This can put the ovary's blood supply at risk.‌

It's not always easy to tell when you have a teratoma. They often look like cysts, or they may not be visible at all.

Teratomas may be found before birth with an ultrasound, at birth when they're visible, or during a regular physical or pelvic exam.

If you see a lump on your body or that of your child, or notice pain or swelling, book a doctor's appointment. If the doctor suspects a teratoma, they'll ask questions about your general health and medical history and do a physical exam.

Your doctor may also request:

  • Imaging tests like X-ray, ultrasound, bone scans, MRI, and CT to see where the tumor is
  • Blood tests to check hormone levels that may indicate a tumor
  • Biopsy to see if the tumor is cancerous

Treatment of a teratoma depends on a few things, including where it is, how large it is, and its risk of being cancerous. A small tumor that isn't causing symptoms may not need treatment, but your doctor will keep an eye on it.

If your tumor has spread, is cancerous, or is likely to become cancerous, your doctor may suggest removing it through surgery. They may also suggest treating it with chemotherapy and radiation. Your treatment will depend on your age, health, and medical history.

A teratoma is a rare type of tumor that can grow on your tailbone, ovaries, or testicles or in other places on your body. They form from germ cells, which can develop into any type of cell in the body. That's why you can have a teratoma with hair, teeth, bone, and other types of tissues. Most aren't cancerous but some are. See your doctor if you have unexplained swelling, pain, or bleeding.

Is a teratoma an undeveloped baby?

Teratomas are not undeveloped babies. The very rare fetiform type can look a lot like a malformed fetus. But it doesn't have an amniotic sac or placenta, so it's not possible for it to grow and develop. This type of tumor might be confused with a parasitic twin or fetus in fetu. This is a rare condition in which a twin that was unable to develop gets absorbed by the body of its surviving sibling while in the womb.

How common is a teratoma?

They're rare. For example, the fetiform type only affects about 1 out of every 500,000 people. A mature cystic ovarian teratoma affects between 1 and 14 out of every 100,000 people each year. Tailbone teratoma, the most common type in children, affects 1 in 40,000 newborn babies.

Can teratomas have eyes?

They can contain parts of eyes, as well as parts of organs like the brain, liver, or thyroid gland. But there are no recorded case of a complete eye or organ within a teratoma tumor.