Lesional epilepsy: the effects of surgical intervention on ictal onset zone and permissive neural networks

Epilepsy is common in patients with circumscribed brain abnormalities, such as
primary brain tumours and focal cortical dysplasias. In a substantial number of
these patients, anti-epileptic drug treatment is ineffective. Patients with
lesional epilepsy in whom no brain tumour is present will be referred to
epilepsy surgery programs. The aim of these programs is to (1) identify and,
subsequently, (2) remove the ictal zone. This leads to long-term seizure
freedom in only 30-60% of patients.
Although in patients with brain tumours the primary aim of surgery is the
removal of the tumour, it is increasingly acknowledged that resective surgery
may also result in a decrease of seizure frequency. For both patient groups,
improvement of outcome of epilepsy surgery will therefore be extremely
relevant.
Electrocorticography (ECoG) and magnetoencephalography (MEG) are imaging
techniques that are used for detection of seizure activity and epileptic source
localization as well as assessment of functional connectivity and neural
network features throughout the brain. Recent research advances concerning
functional connectivity and network properties of the brain have indicated that
these techniques may be used for epileptic source localization and to
investigate factors that determine the frequency of epileptic seizures.
Application of these methods in candidates for epilepsy surgery may lead to
more effective treatment and improvement of surgical outcome.

The primary objective of this study is to characterize functional brain
networks in patients considered for (i) epilepsy surgery and (ii) tumour
surgery with epilepsy surgery techniques. Characterization will be done
preoperatively (MEG), during surgery (ECoG) and post surgery (MEG). At each
stage, networks will be characterized using graph theoretical measures that are
expected to be related to seizure proneness.
The secondary objectives of this study are: (1) To relate network properties at
different stages to (i) seizure frequency, (ii) seizure burden, and (iii)
cognition; (2) To develop a model to predict the effect of surgery on network
changes and reduction of seizure burden.

This is a longitudinal observational study.

For patients, the burden associated with participation consists of a number of
visits to the outpatients* clinic for three MEG and MRI measurements, an ECoG
and two neuropsychological screenings. It should be stressed that the ECoG,
first MEG measurement as well as the first two MRI measurements are already
part of routine practice in epilepsy patients. Furthermore, patients will be
asked to keep a diary regarding the frequency and severity of epileptic
seizures during the course of their disease. No health-related risks are
involved in this study. In our view, the burden associated with participation
is proportionate to the potential value of the research for patients suffering
from epilepsy.