Epilepsy surgery.

Abstract

Surgical therapy of epilepsy, although still underutilized, is presently well accepted and performed world-wide with increasing frequency. In the last decade the following changes have been noticed: non-invasive pre-surgical evaluation is increasingly carried out in close collaboration with referring centres so that often no (or only a very short) hospitalization is necessary in highly specialized epilepsy centres for this purpose. Stereoelectro-encephalography (SEEG) is used less often in invasive evaluation while the subdural strip and grid electrode-techniques are used more often. There is a general trend for a more flexible and collaborative multidisciplinary and multi-method approach utilizing the whole spectrum of modern diagnostic facilities in a more patient-oriented and therefore more cost-effective way. The main objective of the pre-surgical evaluation is to determine the onset area of the patient's spontaneous habitual seizures. The primary epileptogenic zone is not necessarily synonymous with the so-called lesional zone, although in the great majority of patients they are related. In a small percentage of candidates for epilepsy surgery additional special examinations are necessary to prevent and/or predict the degree of post-operative deficits. At present selective Amytal tests are often used but these invasive procedures might be replaced in the future by functional PET and functional MR studies. Surgery in patients with epilepsy can be categorized into: (i) lesion-oriented surgery (lesionectomy sensu stricto), (ii) epilepsy-oriented lesional surgery, (iii) surgery for epilepsy sensu stricto. Surgery is performed with a 'curative (= causal)' or a 'palliative' intention. Furthermore surgery can be categorized into standardized epilepsy surgery (such as anterior temporal lobe resection, selective amygdalohippeocampectomy, anterior callosotomy); and individually tailored surgical interventions. It is obvious that also so-called standardized operations are tailored to some degree, usually based on pre-operative findings as well as on intraoperative corticography and/or other intra-operative neurophysiological tests (functional mapping). Individually tailored operations comprise smaller topectomies and larger resections. Surgery for temporal lobe epilepsy still prevails. For mesial temporal lobe epilepsy more selective operations, such as the selective amygdalohippocampectomy, are increasingly performed. Today the majority of patients suffering from this syndrome can be evaluated non-invasively (or 'semi-invasively' with the foramen ovale electrode technique) in combination with MRI (including volumetry of the hippocampus) and PET or SPECT. In general one has the impression that extratemporal resections without a lesion are performed less often. But, if a morphological abnormality is present, pre-surgical evaluation (using grids), and surgery making use of 'functional mapping' are increasingly offered from more and more centres. Anterior callosal sections and functional hemispherectomies have also witnessed a renaissance. The most important standardized operations are reviewed.