A miniature brain, skull and hair have been found inside a tumour growing on the ovary of a 16-year-old girl.
The growth was discovered when the teenager, from Japan, had routine surgery to remove her appendix, reports the New Scientist.
When doctors cut the 10cm-wide tumour out, they found clumps of hair alongside the underdeveloped brain and a thin outer plate of bone.
A closer inspection revealed brain cells had organised themselves into a small version of a cerebellum , the part that sits under the brain’s two hemispheres.
It was developed enough that electric impulses could be sent between neurons, according to Masayuki Shintaku, the doctor who studied the tumour.
A structure had also formed that resembled a brain stem, the part of the organ that connects to the spinal cord.
Tumours found on ovaries are normally harmless, though the cause of them is still unknown. Brain cells are often found in these growths, but it is very unusual for them to arrange into brain-like structures.
Angelique Riepsamen, a doctor at the University of New South Wales, told the New Scientist: “Neural elements similar to that of the central nervous system are frequently reported in ovarian teratomas, but structures resembling the adult brain are rare.”
The teenager did not experience any symptoms, despite previous reports of women with the same issue suffering from paranoid thoughts, agitation or memory loss.
These symptoms occur when immune cells begin to attack the “foreign” brain, but accidentally end up attacking the patient’s real brain too.
The tumour has been removed and the girl is recovering well.
The case was originally published in the journal Neuropathology.
