Page 448 - ILAE_Lectures_2015

Chapter 45

Pre-operative evaluation and outcome of surgical treatment of
epilepsy

MATTHEW C. WALKER and DAVID R. FISH

Institute of Neurology, University College London, National Hospital for Neurology and
Neurosurgery, Queen Square, London
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It has been estimated that there are approximately 7501500 new cases per annum in the UK
who could benefit from epilepsy surgery, and who thus require presurgical assessment.
Others may require surgery regardless of seizure control for removal of a progressive lesion
(e.g. tumour) or a lesion that has other inherent risks such as danger of haemorrhage (e.g.
arteriovenous malformation).

The purpose of pre-operative evaluation is three-fold:
1) to assess the potential for operative success
2) to identify the most suitable type of operation
3) to assess the risk-benefits of such an operation.

Patient selection

The principles for patient selection are:

Drug resistant seizures. Before someone can be considered drug resistant, there has to be an
adequate trial of therapy; there is, however, some debate as to what constitutes an adequate
trial of therapy. Most centres would consider treatment with at least two first-line antiepileptic
drugs (AEDs) appropriate to the type of epilepsy over a period of two years. This is because
the chance of a patient becoming seizure free diminishes if control is not achieved with initial
therapies, and evaluation for surgery should not be delayed while every possible combination
of medication is tried.

Seizure frequency and severity such as to cause significant social and medical disability. It
is again difficult to be proscriptive here, and each case needs to be discussed on an individual
basis. It is important to remember that there is not only an associated morbidity attached to
seizures, but also an associated mortality (including sudden unexpected death, or SUDEP)
that may be higher than 1% per annum for the type of patients undergoing pre-surgical
assessment.

Reducing or stopping the seizures would result in a significant improvement in quality of life.
Severe learning difficulties and psychiatric disease are relative contraindications, as seizures
may constitute a minor part of the person’s disability. Furthermore there has to be a realistic
view of the possible benefits by both patient and carers. Careful counselling to assess and to
inform patient expectations is necessary before surgery.

Convergent data from different investigative modalities localise the epileptogenic zone. This
important for curative epilepsy surgery (see below), but is of lesser importance for palliative
surgery such as corpus callosotomy and vagal nerve stimulation.