The etiology of focal seizures is usually identified in only about one third of cases.
Traumatic brain injury is an increasingly common etiology for focal seizures.
Penetrating head injuries have the highest risk for the development of epilepsy.
For a closed head injury to carry a significant seizure risk, there should be loss of consciousness or amnesia lasting longer than 30 minutes.
A slight elevation in risk may be present even with <30 minutes of amnesia.
CNS infection may result in focal seizures. The presumed mechanism is a CNS insult, which sets up an epileptogenic focus.The more complicated the CNS infection, the more likely that it will contribute to seizure development.
Brain tumors are another source of focal seizures: low-grade tumors seem more epileptogenic than high-grade tumors.
Although not completely assessed, case series have suggested that 28% of patients undergoing surgery for brain tumors suffer from seizures.
Focal seizures may also develop after a stroke. Risk for seizure activity is at least 3 times higher after stroke, but prophylactic antiepileptic drug therapy is typically not recommended.
Both Alzheimer disease (AD) and non-AD dementia have been associated with seizure development.
Perinatal injuries seem to contribute to the development of epilepsy only when there is coexistent neurologic handicap (e.g., cerebral palsy). Family history is also related to the development of focal epilepsy, although this is not a simple relationship. Some syndromes are thought to be due to a single gene inheritance (familial temporal lobe epilepsy), while others have a complex inheritance (idiopathic partial epilepsies and cryptogenic/symptomatic partial epilepsies).
Benign focal epilepsies of childhood refers to a group of idiopathic syndromes known to cause focal seizures in developmentally and neurologically normal children. They include benign childhood epilepsy with centrotemporal spikes and childhood epilepsy with occipital paroxysms. These syndromes follow a benign course and usually remit prior to adulthood.
Neurocutaneous syndromes such as neurofibromatosis, Sturge-Weber syndrome, and tuberous sclerosis may result in focal or generalized seizures. Although some intracranial arteriovenous malformations are largely asymptomatic, others, including cavernous hemangiomas, do carry a risk of seizures.