There are a number of causes that can be linked to anger but traumatic brain injury can lead to severe mood swings and lack of control over some emotions which your son could be going through. It is very normal for patients who have undergone brain surgery to be experience episodes of anger. Learn more from http://main.uab.edu/tbi/show.asp?durki=10170.
Unfortunately yes, especially if there was frontal brain injury. If you are describing uncontrolled anger or rage type outbursts, I suggest that you seek medical help on this. There also appears to be a high incidence of childhood head injuries in people with Borderline Personality Disorder--characterized in part by rage, anger and outbursts.