A 16-year old girl went in for a routine appendectomy and came out with a surprising discovery about a rare growth within her body. When doctors opened the girl’s abdomen to take out her appendix, they discovered what’s known as a fetiform teratoma, otherwise known as a homunculus. These growths are a rare type of tumor which grow various human tissues and can even take the rough shape of a human body. This particular 10 centimeter (4 inch) tumor had a tiny, half-formed skull inside complete with a half-formed brain and even a shock of hair. One end of the brain even resembled a brain stem.
According to the case study about the tumor recently published in the journal Neuropathology, this particular tumor is extremely rare due to how “well-formed” the tiny cerebellum found inside was:
The well-formed cerebellum and brainstem-like structures found in the present case represent extreme examples [...] In the present case, the similarity of the cerebellar tissue in the teratoma to the normal cerebellum was evident at the ultrastructural level, and largely unmyelinated nerve fibers and abundant, well-formed synaptic complexes were demonstrated.
In other words, this wasn’t just a lump of brain cells, it was a full-on tiny, creepy little brain. While most teratomas don’t present any other symptoms, some women with homunculus teratomas have reported experiencing paranoia, confusion, and personality changes. Could these tiny, half-formed brains be affecting the thoughts of their hosts? The prevailing theory is that the body produces antibodies to attack each particular type of tissue in a teratoma; thus, when brain tissue is present, those antibodies can attack the host's brain itself aside from the tiny, tumor brain. Much is still unknown about these rare and disgusting tumors.
These teratoma tumors are most commonly found in testes in men and ovaries in women due to the abundance in those organs of germ cells, the cells responsible for producing eggs and sperm. For some mysterious reason, these cells sometimes cause the abnormal growth of other types of cells which can form tissues. While hair and teeth are the most common tissues found within tumors, some fetiform teratomas have been found with near-complete, doll-like human forms inside. See mom? This is why I didn’t become a doctor. No thanks.