Teratoma natural history

Natural history
Teratomas belong to a class of tumors known as nonseminomatous germ cell tumor (NSGCT). All tumors of this class are the result of abnormal development of pluripotent cells: germ cells and embryonal cells. Teratomas of embryonal origin are congenital; teratomas of germ cell origin may or may not be congenital (this is not known). The kind of pluripotent cell appears to be unimportant, apart from constraining the location of the teratoma in the body.

Location and incidence


Teratomas derived from germ cells occur in the testes in males and ovaries in females. Teratomas derived from embryonal cells usually occur on the body midline: in the brain, elsewhere inside the skull, in the nose, in the tongue, under the tongue, and in the neck (cervical teratoma), mediastinum, retroperitoneum, and attached to the coccyx. However, teratomas may also occur elsewhere: very rarely in solid organs (most notably the heart and liver) and hollow organs (such as the stomach and bladder), and more commonly on the skull sutures. Embryonal teratomas most commonly occur in the sacrococcygeal region: sacrococcygeal teratoma is the single most common tumor found in newborn babies.

Of teratomas on the skull sutures, approximately 50% are found in or adjacent to the orbit. Limbal dermoid is a choristoma, not a teratoma.

Teratoma qualifies as a rare disease, but is not extremely rare. Sacrococcygeal teratoma alone is diagnosed at birth in 1 out of 40,000 babies. Given the current world population birth rate, this equals 5 per day or 1800 per year. Add to that number sacrococcygeal teratomas diagnosed later in life, and teratomas in other locations, and the incidence approaches 10,000 new diagnoses of teratoma per year.

Hypotheses of origin
Concerning the origin of teratomas, there exist numerous hypotheses. These hypotheses are not to be confused with the unrelated hypothesis that fetus in fetu (see below) is not a teratoma at all but rather a parasitic twin.

Dermoid cyst
A dermoid cyst is a mature teratoma containing hair (sometimes very abundant) and other structures characteristic of normal skin and other tissues derived from the ectoderm. The term is most often applied to teratoma on the skull sutures and in the ovaries of females.

Fetus in fetu and fetiform teratoma
Fetus in fetu and fetiform teratoma are rare forms of mature teratoma that include one or more components resembling a malformed fetus. Both forms may contain or appear to contain complete organ systems, even major body parts such as torso or limbs. Fetus in fetu differs from fetiform teratoma in having an apparent spine and bilateral symmetry.

Most authorities agree that fetiform teratomas are highly developed mature teratomas; the natural history of fetus in fetu, however, is controversial. There also may be a cultural difference, with fetiform teratoma being reported more often in ovarian teratomas (by gynecologists) and fetus in fetu being reported more often in retroperitoneal teratomas (by general surgeons). Fetus in fetu has often been interpreted as a fetus growing within its twin. As such, this interpretation assumes a special complication of twinning, one of several grouped under the term parasitic twin. In this regard, it is noteworthy that in many cases the fetus in fetu is reported to occupy a fluid-filled cyst within a mature teratoma. Cysts within mature teratoma have also been reported to contain a rudimentary beating heart.

Regardless of whether fetus in fetu and fetiform teratoma are one entity or two, they are distinct from and not to be confused with ectopic pregnancy.

Struma ovarii
A struma ovarii (literally: goitre of the ovary) is a rare form of mature teratoma that contains mostly thyroid tissue. Despite its name, struma ovarii is not restricted to the ovary. Only 5% of struma ovarii are malignant.

Complications
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). The mass effect frequently consists of obstruction of normal passage of fluids from surrounding organs. The vascular steal can place a strain on the growing heart of the fetus, even resulting in heart failure, and thus must be monitored by fetal echocardiography.

After surgery, there is a risk of regrowth in place, or in nearby organs.

Prognosis
The prognosis of teratoma depends on the following:


 * Whether or not the tumor can be removed by surgery.
 * The size and location of the tumor
 * The patient’s general health