Locked-in syndrome is usually the result of a brain stem stroke that affects the pons or another injury to the same area of the brain. People with locked-in syndrome have little or no control over their motor movements, causing quadriplegia. They also cannot speak but remain cognitively intact.
that all i could find and i dont think its a tumor be you have to have a serious acident or be born with it. there is also no cure for it. but it is known that a few people have covered from it.
hope this helps!