Look at the giant black hole in this woman's brain, above. That's where her cerebellum should be. It's the brain region critical for movement and coordination. And apparently, it's possible for a person to live without it.
In a case study recently published in the journal Brain, a Chinese group of researchers describes a 24-year-old woman who had no idea that there was anything unusual about her brain until she went to the ER one day with symptoms of nausea and vomiting.
Brain scans revealed that she had no cerebellum, as you can see in the picture above. Not only was she alive, but she was mostly healthy except for dizziness and an unsteady gait that's been with her most of her life.
The paper notes that she's one of only nine recorded cases in the medical literature of someone surviving without a cerebellum.
Granted, it's entirely possible that there are other cases out there that have never been diagnosed. Unless someone ends up getting a brain scan or an exceptionally thorough autopsy, a person might never know that a huge chunk of his or her brain was missing.
This case study in Brain is an excellent example of how surprisingly adaptable the brain can sometimes be, especially with abnormalities that happen earlier in life. Whereas many scientists used to think of the brain as having permanent regions that do very particular tasks, it turns out that many parts of the brain can do all sorts of different tasks — if they have to.
For example, surgeons have sometimes removed half the brain to stop severe recurring seizures in children. That's one version of a procedure called a hemispherectomy. (The cerebellum is left behind in these cases.)
After the surgery, the remaining brain cells can sometimes take over many of the functions that had previously been performed by the removed parts. Children's brains are especially malleable in this regard, compared with adults'. If a hemisphere is removed, some children may lose movement on the opposite side of their bodies, but many are still able to normally walk and talk — and they keep their personality, too.
H/t Helen Thomson for her New Scientist story that called my attention to this cerebellum paper.