Brain swelling is the common name of what is medically called a "cerebral edema"  It is usually the result of many different kind of injuries to the brain. Many times, brain swelling is unavoidable and if it is not controlled can lead to death because of the excessive pressure in the head (intracranial pressure).  The swelling is caused by damaged tissue to the brain trying to take in more blood (oxygen rich nutrients) to repair the damaged axonal tissue.  The problem becomes the pressure because the skull is an enclosed environment.