Focal seizures, also known as partial seizures or localized seizures, are a type of seizure that initially affects only one hemisphere of the brain. The brain is divided into two hemispheres, each consisting of four lobes - the frontal, temporal, parietal, and occipital lobes. A focal seizure is generated in and affects just one part of the brain, either a whole hemisphere or part of a lobe.
Focal seizures can be categorized into two main types: focal onset aware and focal onset impaired awareness. In focal onset aware seizures, a small part of one of the lobes may be affected, and the person remains conscious. This type of seizure can often be a precursor to a larger focal onset impaired awareness seizure.
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Focal onset aware seizures (simple partial seizures): These seizures begin in one side of the brain, and the person experiencing them is fully awake, alert, and able to recall events during the seizure. Some individuals may be "frozen" during the seizure, making it difficult to respond to others.
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Focal onset impaired awareness seizures (complex partial seizures): This type of seizure is often preceded by a focal onset aware seizure (aura). Patients experiencing a complex focal seizure may stare blankly into space or experience altered consciousness.
Focal seizures can be caused by various factors, including stroke, head injuries, brain tumors, and blood vessel disease of the brain. The symptoms of a focal seizure depend on the area of the brain that is affected. In some cases, a focal seizure can progress to a generalized tonic-clonic seizure, which affects the whole brain. This is called secondary generalization.
