Surgery of an ovarian teratoma A tumour that is originating from germ cells is called a teratoma. It may contain components of all three germ layers.
One does differentiate between mature and immature teratomas. Mature teratomas consist of differentiated tissues, e.g. skin, hair, teeth, muscular- and nervous tissue. Rarely some teratomes can have complex structures such as eyes, hands, feet or other extremeties and organs.
Usually teratomas are encapsuled in a cystic way, where the walls are lined with epithelial cells. Sometimes there are teratomas that feature both cystic and solid parts.
Teratomas in female organs, e.g. in the ovaries, are most commonly well differentiated and benign. Only 3% of teratomas in women are malign, whereas in men the teratomas, such as in the testicles (also called teratoma carcinoma) are mostly undifferentiated and malign.
There are teratomas which consist of more than one kind of tissue, on the other hand there are also monodermal teratomas such as the dermoid cyst. Another special form of teratoma is the so-called fetiform teratoma, where the teratoma looks like an malformed fetus due to its very well differentiated tissues.
There is a big debate if described cases of Fetus in fetu are in relationship with fetiform teratomas or if there is an actual adhesion of two foetuses while pregnancy.