Neuroradiology

Epilepsy

term derived from the Greek word epilepsia meaning "to take hold of or to seize". Epilepsy defines a condition in which an individual experiences recurrent unprovoked seizures.

A seizure is a distinct transient clinical attack characterized by abnormal movements of the body, sudden cessation of ongoing conscious activity and memory disturbances, due to excessive abnormal electrical discharge of the brain. Therefore, the terms epilepsy and seizure are not synonymous and a single seizure attack is not sufficient to classify a patient as epileptic.

Epilepsy is a common neurological disorder (0.5-1% of the world population). Known causes of epilepsy are: mesial temporal sclerosis, cortical developmental venous anomaly, tuberous sclerosis, hypoxia perinatal, tumours, traumatic scarring, vascular malformation intracranial and infections.

There are two classification schemes for epilepsy. The first groups patients according to epilepsy syndromes which are defined by clinical characteristics of seizures, age of onset, interictal and ictal EEG picture and presence of underlying brain lesions.

The second classification produced by the International League Against Epilepsy in 1989 divides epilepsies, based on the type of seizures, in:

  • generalized, with initial simultaneous neuronal activation in both hemispheres; and

     

  • partial with a focal initial activation in the cortex.

    Both types are further subcategorized into idiopathic (presumed genetic), symptomatic (presumably related to a structural brain lesion) and cryptogenetic (in which a structural disorder of the brain is suspected but not documented by neuroradiological studies).

    The distinction between different types of epilepsies is critical because they require different radiological and therapeutic approaches. Generalized seizures can usually be well controlled by medical treatment; on the contrary 3050% of patients with partial seizures have medically refractory epilepsy and they are potential candidates for surgical treatment.

    All epileptic patients should be investigated by EEG. In suspected symptomatic epilepy neuroradiological investigation is mandatory. CT scan is able to show some epileptogenic lesions but at present MR is the best imaging modality to detect and delineate brain lesions. CT scan better defines calcific components and skull remodelling.

    In patients selected for surgery technical investigations should focus on the localization of the epileptogenic zone (EZ) and the epileptogenic lesion. The EZ is the cortical area of origin and spreading of the abnormal electrical discharges, which must be completely resected at surgery, and is defined on the basis of EEG recording (interictal and ictal EEG, video-EEG, stereo-EEG). The EZ and epileptogenic lesion are not synonymous; they may be closely related, but the EZ is usually larger and includes the structural lesion.

     

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