Epilepsy Program

Localizing the Seizure Focus

The key to epilepsy surgery is localization of the seizure focus. Typically, seizures that can be cured with surgery will arise from one of the inner portions of the temporal lobe, either left or right. Bilateral seizures, those that sometimes start on the left and sometimes start on the right, are not amenable to surgery because removal of both temporal lobes creates very severe memory problems. The path of the spread of a seizure is not critically important to outcomes of seizure surgery. The surgical target is the seizure focus, the place at which the seizure originates. Secondarily generalized tonic-clonic seizures will stop if the focal point of origin is removed.

One type of epilepsy surgery is a partial temporal lobectomy. Surgeons sometimes can cure seizures with operations on other regions of the brain, but the targets and boundaries of surgery are less clear than they are in temporal lobe surgery. An exception to this is surgery in the area of a lesion. Such lesions may be malformed blood vessels, post-traumatic scars, low-grade brain tumors, prior brain abscesses, or developmental lesions, such as migration problems, dysplasias, and heterotopias. Surgery around well-circumscribed lesions is often quite successful.

To evaluate a patient for temporal lobe surgery, the first key is to make certain that they have epilepsy and not one of its imitators, such as psychogenic (non-epileptic) seizures. EEG may help to localize the focus. Although interictal spikes, which are abnormal electrical signals that can at times be seen between seizures, are suggestive of where seizures come from, they are not as reliable as the electrical activity at the start of a seizure. For that reason, surgical candidates usually undergo video-EEG monitoring as an inpatient in order to capture five or six of their typical seizures.

Medications may be reduced or discontinued while undergoing monitoring, in order to provoke seizures. The hope is to find that all seizures come from some recognizable spot at the anterior to mid portion of one temporal lobe. MRI can be useful to rule out causative lesions and to show a subtle form of scarring in the temporal lobe called mesial temporal sclerosis. This is not always present, but when it is present, it is a strong indication that temporal lobe is involved in the epilepsy.

Neuropsychological tests are performed to determine whether a patient has impairments in the verbal sphere, usually reflecting injury to the dominant left hemisphere, or in the sphere of picture, face and shape recognition, which usually reflects right hemisphere damage.

Neuropsychological testing can screen for depression, which is highly prevalent in this population. Psychosocial adjustment after epilepsy surgery is key to the success of the procedure, since the goal is improvement of quality of life, rather than just attenuation of seizures.

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