There are many reasons to perform a craniotomy surgery procedure, including but not limited to the following:
Brain tumor detection, removal, or treatment.
Taking out blood or blood clots from a blood vessel that is leaking.
Draining a brain abscess
Repairing a tear in the membrane lining
Repairing skull fractures
Treating epilepsy
Putting stimulator implants to treat movement problems.
Clipping or repairing of an aneurysm