The following information is from BrainInjury.Com
Unfortunately, seizures may develop immediately after an injury to the brain or may develop in delayed fashion, showing up months or years after the initial trauma. Generally speaking, the risk of post traumatic seizures is related to the severity of the injury- the greater the injury, the higher the risk of developing seizures. Even mild to moderate injuries can result in seizures.
There are many kinds of seizures and seizures are not an uncommon condition among persons without head injuries. It is thought that a head injury disrupts the pathways of the brain and that an epileptic seizure can be viewed as a sort of short circuit of the brain's electrical functioning. During the seizure the electrical fields in the brain are overloaded, resulting in seizures.
The most commonly seen seizures related to traumatic brain injury are "generalized" seizures, which are also called "Tonic-Clonic" or "Grand Mal" seizures. The classification of different types of seizures is beyond the scope of this website.
Persons who have had head trauma are twelve times as likely as the general population to suffer seizures (Willmore, 1992). Patients with acute intra cranial hematomas also have a high rate of epilepsy. While there are contradictory studies, the more recent study (Lee, 1992) showed that of 4,232 persons suffering mild closed head injury, 53% had early post-traumatic epilepsy. Approximately 57% of head injured individuals developed epilepsy within one-year of injury. Longer onset epilepsy beginning more than four years after the trauma occurs in 20% of patients who developed epilepsy. It is estimated that 30% of all individuals suffering head trauma developed post-traumatic seizures and 80% of the time they occur within the first 24-months (Bakay, 1980).