Teratomas of embryonal origin are most often found in babies at birth, in young children, and, since the advent of ultrasound imaging, in fetuses. The most diagnosed fetal teratomas are sacrococcygeal teratoma (Altman types I, II, and III) and cervical (neck) teratoma. Because these teratomas project from the fetal body into the surrounding amniotic fluid, they can be seen during routine prenatal ultrasound exams. Teratomas within the fetal body are less easily seen with ultrasound;  for these, MRI of the pregnant uterus is more informative. Complications
Teratomas are not dangerous for the fetus unless either a mass effect occurs or a large amount of blood flows 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, thus must be monitored by fetal echocardiography. Teratomas can cause an autoimmune illness called  N-methyl-D-aspartate (NMDA) receptor encephalitis. In this condition, the teratomas may contain B cells with NMDA-receptor specificities.After surgery,  a risk exists of regrowth in place, or in nearby organs. Pathophysiology
Teratomas belong to a class of tumors known as nonseminomatous germ cell tumor. All tumors of this class are the result of abnormal development of pluripotent cells: germ cells and embryonal cells. Teratomas of embryonic origin are congenital; teratomas of germ cell origin may or may not be congenital.
A teratoma is a tumor made up of several different types of tissue, such as hair, muscle, teeth, or bone. Teratomata typically form in the ovary, testicle, or coccyx. Symptoms
Symptoms may be minimal if the tumor is small. A testicular teratoma may present as a painless lump. Complications may include ovarian torsion, testicular torsion, or hydrops fetalis.They are a type of germ cell tumor (a tumor that begins in the cells that give rise to sperm or eggs). They are divided into two types: mature and immature. Mature teratomas include dermoid cysts and are generally benign. Immature teratomas may be cancerous. Most ovarian teratomas are mature. In adults, testicular teratomas are generally cancerous. Definitive diagnosis is based on a tissue biopsy.Treatment of coccyx, testicular, and ovarian teratomas is generally by surgery. Testicular and immature ovarian teratomas are also frequently treated with chemotherapy.Teratomas occur in the coccyx in about one in 30,000 newborns, making them one of the most common tumors in this age group. Females are affected more often than males. Ovarian teratomas represent about a quarter of ovarian tumors and are typically noticed during middle age. Testicular teratomas represent almost half of testicular cancers. They can occur in both children and adults. The term comes from the Greek word for "monster" plus the "-oma" suffix used for tumors. Types
Mature teratoma
A mature teratoma is a grade 0 teratoma. They are highly variable in form and histology, and may be solid, cystic, or a combination of the two.