Doctors in Japan have found a miniature brain developing inside a tumor taken from the ovary of a 16-year-old girl.
The unusual discovery was made while an operation was being conducted to remove the girl's appendix, the New Scientist reported.
The tumor was approximately 3 inches wide, of which 1 inch was the miniature skull, which contained highly organized neural tissue.
“Three layers of the cerebellar cortex were well formed,” the researchers wrote of the tumor, according to IFL Science.
The cerebellum normally sits under the brain's two hemispheres.
The fibers which connect neural cells together, allowing electric impulses to transmit between them, were also beginning to develop.
Tumors found in the ovaries with foreign cell tissue are known as teratomas.
"Neural elements similar to that of the central nervous system are frequently reported in ovarian teratomas, but structures resembling the adult brain are rare," said Angelique Riepsamen from the University of New South Wales, New Scientist reported.
Approximately one-fifth of all ovarian tumors contain foreign objects like teeth, cartilage, muscle, fat and hair.
One theory proposed to explain the emergence of teratomas is that immature egg cells sometimes go rogue and produce different body parts.
The 16-year-old patient did not experience any symptoms prior to the operation. In rare cases, doctors have reported women experiencing mental health problems including confusion, memory loss, paranoia and agitation. Such symptoms can be caused by attacks from the immune system, which recognizes brain cells in the ovaries but can sometimes also attack the brain itself.
Usually, removing the tumor will eliminate these symptoms.
The 16-year-old girl recovered well from the operation.