A teratoma is a congenital (present at birth) tumor. This tumor contains three layers of tissue and can contain teeth, hair, eyes, and/or bones. Because of these common findings and the fact that teratomas form in the embryonic stage, there is a myth that these tumors are an embryo themselves or a twin, but that is false. Even though all teratomas are congenital, some are not discovered until later in life. This is true for particularly small teratomas. They can form on any area of the body but are most commonly found at the base of the coccyx (tailbone), on the ovaries of girls, and the testes of boys. Most teratomas are benign, but some can be malignant. Benign teratomas grow aggressively, but do not spread; whereas malignant ones both grow aggressively and can spread to other parts of the body.
Teratomas, even ones deemed benign, do come with a increased chance of reoccurrence of malignant tumors. The finding of a malignant teratoma increase this chance even more. Challenges also arise if the teratoma is located in a inaccessible location or one that causes pressure to be placed on a vital organ or the nervous system.
Although often benign, any teratoma have the potential to be malignant. Therefore adequate follow up requires close observation, repeated physical examination, scanning (MRI, CT, or ultrasound, and blood tests).