What Is It, Signs, Symptoms, and More

Author:Anna Hernández, MD

Editors:Alyssa Haag,Emily Miao, PharmD

Illustrator:Jessica Reynolds, MS

Copyeditor:David G. Walker

What is a teratoma?

A teratoma is a type of germ cell tumor that contains different types of tissues, including hair, teeth, eyes, bone, muscle, and neurons. Although teratomas are found primarily in the gonads, they can develop anywhere in the body, especially in midline locations, such as the sacrum, coccyx, mediastinum, retroperitoneum, and central nervous system.

How common are teratomas?

In general, teratomas are rare tumors that typically develop in children. The two most common teratomas are sacrococcygeal teratomas (extragonadal) and mature cystic teratomas of the ovary (gonadal). Sacrococcygeal teratomas, which develop at the base of the spine, are the most common tumors found in newborns with an incidence rate of 1 in 20,000 to 40,000 births; whereas mature ovarian teratomas are the most common ovarian tumor in young females, particularly in their second or third decades of life. Other types of teratomas, including testicular and mediastinal teratomas, are much more rare. 

In very rare occasions, a type of teratoma called fetus in fetu (i.e., fetus within a fetus) can occur. This type of teratoma has the appearance of an undeveloped fetus located inside the body of an otherwise healthy human. One view sustains that fetus in fetu teratomas are the remains of a twin that was unable to sustain life and was later encompassed by the surviving sibling, while another view postulates that the mass is a highly developed teratoma

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Are teratomas cancerous?

The behavior of teratomas generally depends on their location and the age of the affected individual. There are actually two subtypes of teratomas: mature and immature. Mature teratomas have fully developed tissues inside them. They usually appear in children and are typically benign; however, when they appear in adults, they tend to be malignant. An exception to this rule are mature ovarian teratomas, also called dermoid cysts, which are the most common ovarian tumors in young females and have little risk of becoming malignant. On the other hand, immature teratomas, which have undifferentiated tissue that develops specifically from immature neural tissue, tend to be malignant and metastasize quickly. 

What causes a teratoma?

The cause of teratomas is not completely understood. However, it is thought that these tumors derive from the three developmental germ layers, called the ectoderm, mesoderm, and endoderm. These germ layers are made of germ cells, which are capable of forming a variety of tissues, including fat, muscle, teeth, nails, and hair. During fetal development, some of these germ cells do not differentiate, thereby retaining the ability to turn into other cell types. These germ cells then migrate through the midline until they reach the primitive gonads where they can remain for decades, eventually developing into eggs or sperm. It is thought that a problem during these cells’ differentiation process could lead to the development of a teratoma, which explains why teratomas may occur in the gonads themselves or along the path of germ cell migration. 

What are the signs and symptoms of a teratoma?

Individuals with a teratoma may remain asymptomatic for a long time and some may never develop any symptoms. When symptoms do occur, however, they vary depending on the location and size of the teratoma. Ovarian teratomas can predispose individuals to an ovarian rupture or torsion, leading to acute pain in the pelvis or abdomen; testicular teratomas can present with a lump or swelling in the testicles; whereas mediastinal teratomas can affect breathing and cardiac function if they grow very large. Finally, sacrococcygeal teratomas can develop even before birth, resulting in a high demand of blood that can potentially lead to fetal heart failure (i.e., hydrops fetalis). When sacrococcygeal teratomas develop after birth, they can lead to progressive lower back pain and symptoms caused by the obstruction of the genitourinary and gastrointestinal tracts. These symptoms include constipation, abdominal pain, and urinary or bowel incontinence. In rare cases, sacrococcygeal tumors can cause muscle weakness in the lower limbs as well as numbness or paresthesias.

How is a teratoma diagnosed?

Diagnosis of teratomas begins with a thorough clinical history and physical examination. In most cases, small teratomas are discovered incidentally when diagnosing another medical condition. First-line investigations include an X-ray, CT scan, or MRI of the affected area in order to see the extent and characteristics of the growth. An imaging hallmark of teratomas is the presence of fat, which is a derivative of the mesoderm. Further laboratory tests may include obtaining levels of serum alpha-fetoprotein (AFP), which is a tumor marker for immature teratomas. Finally, tumor biopsies may be conducted to determine whether the growth is benign or malignant. 

How is a teratoma treated?

Treatment of a teratoma depends on the location, size, and risk of malignancy. For small, asymptomatic teratomas, treatment may involve observation and regular follow-ups to check for evolution. On the other hand, treatment of malignant teratomas typically involves surgery along with chemotherapy and radiation if the tumor has spread. 

What are the most important facts to know about teratomas?

Teratomas are rare tumors derived from more than one germ layer and, thus, contain various kinds of tissues together, including hair, nails, bones, and muscle. They are a subtype of germ cell tumors, and they are divided into mature or immature based on the degree of tissue differentiation. Mature teratomas tend to be benign, whereas immature teratomas are more likely to undergo malignant transformation.

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Related links

Development of the reproductive system
Germ cell ovarian tumor
Ovarian cysts and tumors: Pathology review
Testicular tumors: Pathology review
Ovarian cysts, cancer, and other adnexal masses: Clinical practice

Resources for research and reference

Gurda, G. T., VandenBussche, C. J., Yonescu, R., Gonzalez-Roibon, N., Ellis, C. L., Batista, D. A. S., & Netto, G. J. (2013). Sacrococcygeal teratomas: Clinico-pathological characteristics and isochromosome 12p status. Modern Pathology, 27(4), 562–568. DOI:10.1038/modpathol.2013.171

Khalifa, N. M., Maximous, D. W., & Abd-Elsayed, A. A. (2008). Fetus in fetu: A case report. Journal of Medical Case Reports, 2(1). DOI:10.1186/1752-1947-2-2 

Peterson, C. M., Buckley, C., Holley, S., & Menias, C. O. (2012). Teratomas: A multimodality review. Current Problems in Diagnostic Radiology, 41(6), 210–219. DOI:10.1067/j.cpradiol.2012.02.00

Ulbright T. M. (2004). Gonadal teratomas: A review and speculation. Advances in Anatomic Pathology, 11(1), 10–23. DOI: 10.1097/00125480-200401000-00002