Presurgical Evaluation for Epilepsy

Introduction

Our unit is specialized in the diagnosis and treatment of pharmacoresistant epilepsies. Because of a close collaboration with both universities (Geneva and Lausanne), the whole spectrum of modern diagnostic tools is available. Since beginning our work, more than 600 patients have been evaluated and most have also had operations; 40 to 45% of our patients were children and adolescents.

What is Epilepsy? 

By definition, an epileptic disorder is present if several epileptic seizures occur spontaneously. Epilepsy is a relatively common disease, affecting 0.5 - 1% of the European population, which corresponds to 1.6-3.2 million people! Children and younger people are often affected, but the disorder may also begin at a later time, or even at a late age. There are many different causes of epilepsy, and its careful identification is essential for appropriate treatment. Fortunately, medication satisfactorily control most epileptic disorders, in such a way that there are no more seizures or that the remaining seizures do not interfere with daily life. However, in approximately 20% of all cases, epileptic seizures occur despite good drug compliance, in which case alternative therapeutic choices should be considered, such as surgical epilepsy therapy.

What does epilepsy surgery mean? 

Despite treatment with one or more antiepileptic drugs and good compliance, disabling seizures persist in many patients. This is called pharmacoresistance. In a significant number of cases, a surgical intervention can improve the condition, i.e. removal of epileptic brain tissue with the ultimate goal of seizure-freedom. However, before any intervention, two criteria have to be fulfilled:

  1. Precise localization of the focus
  2. Differentiation against vital cortex (e.g. speech cortex)

When should surgical therapy or in-patient evaluation of the epilepsy disorder be considered?

  • If despite regular intake of several drugs, the seizures still persist
  • If a focal epilepsy is very probable
  • If the concerned patient agrees to a possible surgical therapy
  • The overall goal is postoperative seizure-freedom; in rare cases, the goal has to be formulated more cautiously and consists of reducing seizures or reducing the most disabling type of seizure (e.g. daily drop-attacks with head trauma in patients with an intellectual disability)

 

Which exams encompass pre-operative monitoring? 

Generally speaking, the more precisely the focus can be localized, the higher are the chances of postoperative seizure-freedom - provided that the focus resides in resectable brain tissue. In the majority of cases, non-invasive exams are sufficient to pose the correct diagnosis.

These include:

  • Neurological testing
  • Neuropsychological testing
  • Prolonged video-EEG monitoring
  • High resolution magnetic resonance imaging (MRI)
  • Nuclear imaging (PET, SPECT)
  • Complementary imaging procedures on the basis of MRI

The realization of all exams as well as the recording of several habitual seizures requires 1-2 weeks of hospitalization at the University Hospital of Geneva. 

In 10-20% of all patients, the focus or adjacent vital cortex cannot be precisely localized sufficiently despite this comprehensive battery of tests. In some cases, invasive monitoring could be recommended, i.e. recording seizures using implanted electrodes (implantation by the neurosurgeon). In our laboratory, all invasive techniques are offered (subdural electrodes, depth electrodes, foramen ovale electrodes) which may also identify vital cortex.

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