Traumatic brain injury is just that....a traumatic injury to the brain. This injury can be caused either by an accident (external) or by a stroke or other vascular problem within the brain (my mother has AVM, a congenital vascular malformation in her brain, resulting in her having many stroke-like episodes and a lot of trauma to my life as well). TBI can cause psychological, cognitive, and physical problems.
Like most disorders, there are varying degrees of tbi. The majority of tbi are mild, meaning they only involve a concussion resulting usually from a blow to the head. Effects of mild tbi may include dizziness and short (under one hour) loss of consciousness. Moderate tbi involves a longer loss of consciousness (1-24 hours) and may involve a skull fracture or other complications (brain swelling,etc). Severe tbi involves more than 24 hours of loss of consciousness and frequently results in serious medical complications.
The effects of a brain injury vary significantly among individuals, and there may be many "hidden" effects which are hard even for the victim to see and understand. Brain injury affects the families and other people associated with the victims. It can be a very puzzling and traumatic problem (I know, I've spent the past 10+ years dealing with it, as well as suffered myself from mild tbi from various accidents). Research on the physical and psychological impact of brain injury is ongoing. It is a difficult subject to work with. Someday the topic will be better understood. Hopefully, better methods of working with tbi victims will be devised.