In some patients, particularly those with complex partial epilepsy, despite adequate drug administration (checked by serum levels), recurrent seizures prevent a normal lifestyle; of these a proportion benefit from operation, provided seizures arise from a single focus. Theoretically, removal of the focus abolishes the partial seizure and can prevent progression to a generalised seizure.
Extensive EEG investigation, and imaging with CT, MRI and SPECT or PET scanning helps identify the site of the primary focus. MRI may reveal an underlying structural abnormality (e.g. tumour, AVM, hamartoma or neuronal migration disorder) increasing the likelihood of improvement after operative removal. The discovery of a structural abnormality in itself may indicate the need for operation. In many patients with a temporal focus, MRI can also demonstrate asymmetry between medial temporal structures and signal change in a sclerotic, shrunken hippocampus, later confirmed by histology to show 'mesial temporal sclerosis'. It is not known whether this is the cause of the epilepsy or the result of anoxia during repeated attacks.
Operation is contraindicated in patients with severe mental retardation or with an underlying psychiatric problem.
Temporal Lobectomy: Anter temporal resectio incorporating the eliptogenic focus, is the most comnr employed techniq Over half become seizure free and a further 30% gain
Operative techniques significant improvement in seizure control.
Extra temporal cortical resection:
Incorporates the eleptogenic focus. Usually associated with focal pathology. Over half show some benefit after operation, but results less satisfactory than for temporal resection.
significant improvement in seizure control.
Possible when tests confirm a focus.in medial temporal structures. Less tissue removed than with temporal lobectomy, but no evidence that this improves seizure control or reduces the mild cognitive changes occasionally seen.
Corpus callosal section:
Prevents spread and reverberation of seizure activity between hemispheres. Most useful for patients with generalised atonic, tonic or myoclonic seizures, but only about two-thirds obtain some benefit. Few become seizure free.
Hemispherectomy: Used in children with major irreversible damage to the whole hemisphere. Good results with over 80% becoming seizure free. Despite removing or disconnecting all but the basal ganglia, crude limb movements in the opposite limbs and walking are often preserved.
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