teratoma
Meaning of teratoma: Its tissues are recognizable and in the wrong place, and whether that tissue is fully formed matters less in the testis than in the ovary.
Definition of teratoma
A teratoma is a germ cell tumor that contains tissue types belonging to more than one embryonic layer, so hair, skin, fat, cartilage, muscle, teeth or gut lining can appear inside a single mass. It grows most often in the ovary or testicle, and in newborns at the tailbone. Pathologists classify it as mature or immature.
Where do they arise?
| Site | Who it affects |
|---|---|
| Ovary | A common ovarian tumor in younger women; the mature cystic form is often called a dermoid cyst |
| Testis | Part of the germ cell tumor group in adolescents and adults |
| Tailbone | The commonest tumor of the newborn, found at or before birth |
| Chest and brain | Uncommon, arising in the mediastinum or near the pineal region |
The pattern follows the path germ cells take during development, migrating along the midline toward the developing gonads, which is why teratomas turn up in a line down the middle of the body rather than at random. Because they come from cells able to form any tissue, a germ cell tumor of this kind can contain structures with no business being where they are found.
What do mature and immature mean?
A mature teratoma contains fully formed adult-type tissue: recognizable skin with hair follicles, fat, cartilage, thyroid tissue or teeth. An immature teratoma contains tissue resembling that of an embryo, most often primitive nerve tissue, and is graded by how much of it is present. The distinction is made by a pathologist examining the tissue, not by imaging, though fat and calcification on a scan can suggest the diagnosis in advance.
Does mature always mean benign?
No, and this is the point most often stated too simply. In the ovary a mature teratoma is benign, and malignant change within one is rare. In a testis after puberty a teratoma forms part of a malignant germ cell tumor and can spread to lymph nodes and lungs even when every part of the tissue looks fully formed, so the same word carries a different weight depending on the site and the age of the person. Behavior in the newborn tailbone tumor depends on how much of it lies inside the pelvis and on whether immature elements are present. Blood markers such as alpha-fetoprotein and human chorionic gonadotropin are measured because they signal other germ cell components mixed in alongside the teratoma. A separate rarity worth knowing is that an ovarian teratoma can provoke an immune attack on the brain, producing an encephalitis that settles once the tumor is removed.
Used in a sentence
Imaging identified an ovarian mass with features suggestive of a mature teratoma.
Good to know
A mature ovarian teratoma is generally benign, but in a testis after puberty a teratoma forms part of a malignant germ cell tumor and can spread even when its tissue appears fully formed, so site and age change what the classification means.
Word origin
Where “teratoma” comes from
Formed from Greek teras, teratos, meaning monster, combined with -oma, meaning tumor, a reference to the tumor's unusual mixture of tissue types.