A teratoma is a rare type of tumor that can contain fully developed tissues and organs, including hair, teeth, muscle, and bone. Teratomas are most common in the tailbone, ovaries, and testicles, but can occur elsewhere in the body.

Teratomas can appear in newborns, children, or adults. They’re more common in females. Teratomas are usually benign in newborns, but may still require surgical removal.

Teratomas are generally described as either mature or immature.

  • Mature teratomas are usually benign (not cancerous). But they may grow back after being surgically removed.
  • Immature teratomas are more likely to develop into a malignant cancer.

Mature teratomas are further classified as:

  • cystic: enclosed in its own fluid-containing sac
  • solid: made up of tissue, but not self-enclosed
  • mixed: containing both solid and cystic parts

Mature cystic teratomas are also called dermoid cysts.

Teratomas may have no symptoms at first. When symptoms develop, they can be different depending on where the teratoma is located. The most common locations for teratomas are the tailbone (coccyx), ovaries, and testicles.

Signs and symptoms common to many teratomas include:

  • pain
  • swelling and bleeding
  • mildly elevated levels of alpha-feroprotein (AFP), a marker for tumors
  • mildly elevated levels of the hormone beta-human chorionic gonadotropin (BhCG)

Here are some symptoms specific to the type of teratoma:

Sacrococcygeal (tailbone) teratoma

A sacrococcygeal teratoma (SCT) is one that develops in the coccyx or tailbone. It’s the most common tumor found in newborns and children, but it’s still rare overall. It occurs in about 1 in every 35,000 to 40,000 infants.

These teratoma can grow outside or inside the body in the tailbone area. Aside from a visible mass, symptoms include:

  • constipation
  • abdominal pain
  • painful urination
  • swelling in the pubic region
  • leg weakness

They’re found more often in infant girls than boys. In one 2015 study of patients treated for SCTs at a Thailand hospital from 1998 to 2012, the female to male ratio was 4 to 1.

Ovarian teratoma

A symptom of ovarian teratoma is intense pain in the pelvis or abdomen. This comes from a twisting pressure on the ovary (ovarian torsion) caused by the growing mass.

Sometimes ovarian teratoma can be accompanied by a rare condition known as NMDA encephalitis. This can produce intense headaches and psychiatric symptoms including confusion and psychosis.

Testicular teratoma

The main symptom of testicular teratoma is a lump or swelling in the testicle. But it may show no symptoms.

Testicular teratoma is most common between the ages of 20 to 30, though it can occur at any age.

Teratomas result from a complication in the body’s growth process, involving the way that your cells differentiate and specialize.

Teratomas arise in your body’s germ cells, which are produced very early in the development of the fetus.

Some of these primitive germ cells become your sperm- and egg-producing cells. But germ cells can also be found elsewhere in the body, especially in the region of the tailbone and the mediastinum (a membrane separating the lungs).

Germ cells are a type of cell known as pluripotent. That means they are capable of differentiating into any type of specialized cell that can be found in your body.

One theory of teratomas suggests that the condition originates in these primordial germ cells. This is called the parthenogenic theory and is now the prevailing view.

It explains how teratomas can be found with hair, wax, teeth, and can even appear as an almost-formed fetus. The location of teratomas also argues for their origin in primitive germ cells.

The twin theory

In about 1 in 500,000 people, a very rare type of teratoma can appear, called fetus in fetu (fetus within a fetus).

This teratoma can have the appearance of a malformed fetus. It’s made up of living tissue. But without the support of a placenta and an amniotic sac, the undeveloped fetus has no chance of development.

One theory explains the fetus in fetu teratoma as the remains of a twin that was unable to develop in the womb, and was encompassed by the body of the surviving child.

An opposing theory explains the fetus in fetu as merely a more developed dermoid cyst. But the high level of development favors the twin theory.

Fetus in fetu only develops in twins who both:

  • have their own sac of amniotic fluid (diamniotic)
  • share the same placenta (monochorionic)

The fetus in fetu teratoma is most often detected in infancy. It can occur in children of either sex. In 90 percent of cases these teratomas are found before the child reaches 18 months of age.

Most fetus in fetu teratomas lack a brain structure. But 91 percent have a spinal column, and 82.5 percent have limb buds.

Remember that teratomas are classified as mature (usually benign) or immature (likely cancerous). The likelihood of cancer depends on where in the body the teratoma is found.

Sacrococcygeal (tailbone) teratoma

SCTs are immature about 20 percent of the time. But even benign ones may need to be removed because of their size, and the possibility of further growth. Although rare, sacrococcygeal teratoma is most often found in newborns.

Ovarian teratoma

Most ovarian teratomas are mature. The mature ovarian teratoma is also known as a dermoid cyst.

About 1 to 3 percent of mature ovarian teratomas are cancerous. They’re usually found in women during their reproductive years.

Immature (malignant) ovarian teratomas are rare. They’re usually found in girls and young women up to the age of 20.

Testicular teratoma

There are two broad types of testicular teratoma: pre- and post-puberty. Pre-puberty or pediatric teratomas are usually mature and noncancerous.

Post-puberty (adult) testicular teratomas are malignant. About two-thirds of men diagnosed with adult teratoma show an advanced state of metastasis (spread) of the cancer.

Diagnosis and discovery depend on where the teratoma is located.

Sacrococcygeal teratoma (SCT)

Large sacrococcygeal teratomas are sometimes detected in ultrasound scans of the fetus. More often they are found at birth.

A common symptom is a swelling at the tailbone, which obstetricians look for in newborns.

Your doctor may use X-ray of the pelvis, ultrasound, and CT scans to help diagnose a teratoma. Blood tests can also be helpful.

Ovarian teratoma

Mature ovarian teratomas (dermoid cysts) usually present no symptoms. They are often discovered during routine gynecologic examinations.

Sometimes large dermoid cysts cause twisting of the ovary (ovarian torsion), which can result in abdominal or pelvic pain.

Testicular teratoma

Testicular teratomas are often discovered accidentally during examination of the testicles for pain from a trauma. These teratomas grow quickly and may present no symptoms at first.

Both benign and malignant testicular teratoma usually cause testicular pain.

Your doctor will examine your testes to feel for atrophy. A firm mass can be a sign of malignancy. Blood tests are used to test for elevated levels of the hormones BhCG and AFP. Ultrasound imaging can help identify the progress of the teratoma.

To check if cancer has spread to other parts of the body, your doctor will request X-rays of your chest and abdomen. Blood tests are also used to check for tumor markers.

Sacrococcygeal teratoma (SCT)

If a teratoma is detected in the fetal stage, your doctor will carefully monitor your pregnancy.

If the teratoma remains small, a normal vaginal delivery will be planned. But if the tumor is large or there’s an excess of amniotic fluid, your doctor will likely plan for an early cesarean delivery.

In rare cases, fetal surgery is needed to remove the SCT before it can cause life-threatening complications.

SCTs that are detected at birth or afterward are removed by surgery. They must be closely monitored, because there’s a significant chance of regrowth within three years.

If the teratoma is malignant, chemotherapy is used along with the surgery. Survival rates are excellent with modern chemotherapy.

Ovarian teratoma

Mature ovarian teratomas (dermoid cysts) are generally removed by laparoscopic surgery, if the cyst is small. This involves a small incision in the abdomen to insert a scope and a small cutting tool.

A small risk of laparoscopic removal is that the cyst can become punctured and leak waxy material. This can result in an inflammatory response known as chemical peritonitis.

In some cases it’s necessary to remove a part or all of the ovary. Ovulation and menstruation will continue from the other ovary.

In 25 percent of cases, dermoid cysts are found in both ovaries. This increases your risk of losing fertility.

Immature ovarian teratomas are usually found in girls up to their early 20s. Even if these teratomas are diagnosed at an advanced stage, most cases are cured by a combination of surgery and chemotherapy.

Testicular teratoma

Surgical removal of the testicle is usually the first treatment for this teratoma when it’s cancerous.

Chemotherapy isn’t very effective for testicular teratoma. Sometimes there’s a mix of teratoma and other cancerous tissue that will require chemotherapy.

Removal of a testicle will affect your sexual health, sperm counts, and fertility. There’s often more than one treatment available, so discuss the options with your doctor.

Teratomas are rare and usually benign. Treatments for cancerous teratomas have improved in recent decades, so most cases can be cured. Informing yourself on the options and seeing an experienced professional are your best guarantee of a successful outcome.