They are created from embryonic cells and the hypothesis is that a cystic teratoma is formed when embryonic cells from a vanished twin are absorbed by the sole survivor and may grow in a random kind of fashion and may even produce teeth, hair and bone but they never make up the normal body shape of a fetus. If a fetus does grow inside the host twin, then it's known as a fetus in fetu.
This is what I said about dermoid cysts in "Womb twin survivors, the lost twin in the Dream of the Womb":
These cysts are smaller than teratomas, and they vary according to how many recognizable tissues can be seen within the cyst. Usually they contain hair and a few teeth, for the cells in a dermoid cyst are from the outer layer of cells known as the ectoderm, which forms into skin, teeth, nails and hair. They are often found on the ovary, in which case they are known as ovarian cysts.
I had a dermoid ovarian cyst, which twisted and ruptured. I had surgery when I wasTeratoma
16. Another tumor developed on the other ovary, which was removed age 18. I had a
vivid imaginary friend until I was 5 or 6. Always felt weird, lonely and different.
I’m not sure why I’m here on this planet.
Recent reports suggest that a teratoma is a less well-developed form of foetus in
foetu. Or conversely, a foetus in foetu is a more developed and differentiated
teratoma. Unlike the foetus in foetu however, some teratomas are comprised of cells
with different chromosomes to the Alpha twin and they may become malignant.
A teratoma can grow to the size of a grapefruit and may contain any kind of tissue, sometimes
organized into a recognizable form, such as hair, or tiny hands or feet. Otherwise there
may be a mass of specific cells that form a specific organ, such as brain, thyroid, liver or
lung cells. In one rare case, a tumour developing externally at the base of a baby’s
spine was opened during surgery to reveal a “rudimentary organ resembling a heart” which
pulsated with a different rhythm to the baby’s own heart.
I think that a teratoma, and a mature cystic teratoma, is formed from the cells of a vanished twin that passed into the body of the survivor.
What do you think?