Focal Seizure

A seizure that begins in networks limited to one cerebral hemisphere. Its symptoms depend on the networks involved and whether awareness is impaired.

Focal Onset: A seizure onset pattern in which abnormal electrical activity begins in networks limited to one cerebral hemisphere. This onset pattern defines focal seizures and distinguishes them from generalized-onset seizures.
Seizure: A transient episode of signs or symptoms caused by abnormal excessive or synchronous neuronal activity in the brain. Focal seizures are one onset-based type of seizure.
Electroencephalography: A method that records electrical activity from the brain using electrodes placed on the scalp or elsewhere. EEG can reveal patterns that support focal onset, although a normal recording does not exclude it.
Generalized-Onset Seizure: A seizure that begins in networks distributed across both cerebral hemispheres. Its bilateral onset contrasts with the one-hemisphere onset of a focal seizure.
Seizure Spread: The propagation of seizure activity from its initial network into additional brain regions. Spread beyond the starting network can change symptoms and involve both hemispheres.
Epilepsy: A brain disorder marked by an enduring predisposition to epileptic seizures and their consequences. A focal seizure may occur in epilepsy, though one seizure alone does not establish the diagnosis.
Magnetic Resonance Imaging: An imaging technique that uses magnetic fields and radio waves to produce detailed images of body structures. Brain MRI can identify lesions associated with focal seizure onset.
Focal to Bilateral Tonic-Clonic Seizure: A seizure that begins focally and then spreads to produce bilateral tonic-clonic activity. Bilateral convulsions can resemble generalized onset, but this seizure starts focally.
Epileptic Focus: A brain region or network implicated in the initiation of epileptic seizures. The focus is the starting point clinicians seek to localize in focal seizures.
Focal Aware Seizure: A focal seizure during which awareness is preserved throughout. Preserved awareness distinguishes this major focal seizure subtype.

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