Dr. Ann McKee of the CTE Center at Boston University presented the findings of her examination of Hernandez's brain on Thursday.
McKee says she could not say Hernandez's behavior was a result of his severe case of chronic traumatic encephalopathy. But she says Hernandez suffered substantial damage to several important parts of the brain, including the frontal lobe.
The former Florida Gators' tight end was found to have stage-three chronic traumatic encephalopathy. Stage four is the most severe form of CTE.
This is the first time doctors say they have seen such an advanced case in a person so young.