This is a teratoma, a type of germ cell tumor that may contain several types of body tissue. Embryonal teratomas most commonly occur in the sacrococcygeal region as it is the single most common tumor found in newly born humans.
Teratomas of germ cell origin are most commonly found in adult men and women.
The tissues of a teratoma, although normal in themselves, may be quite different from surrounding tissues. Teratomas have been reported to contain hair, teeth, bone and, very rarely, more complex organs or processes such as brain matter, eyes, torso, and hands, feet, or other limbs!
Symptoms vary depending on the location. A painful lump or swelling may be apparent. Some babies have a mass that can be seen on an ultrasound before birth. Teratomas are not dangerous for the fetus unless there is either a mass effect or a large amount of blood flow through the tumor, known as vascular steal. This vascular steal can place a strain on the growing heart of the fetus, even resulting in heart failure.
The treatment of choice is complete surgical removal. Teratomas are normally well-encapsulated and non-invasive of surrounding tissues, making them relatively easy to resect from surrounding tissues. Exceptions include teratomas in the brain, and very large, complex teratomas that have pushed into and become interlaced with adjacent muscles and other structures.