Epilepsy surgery can work in 3 different ways:
- By removing the ‘bad’ part of the brain
- Removing the connection of the ‘bad’ part to the other brain areas
- Implanting an electrical stimulator that, through electrical stimulation, reduces the excitability of the ‘bad’ part(s) of the brain.
The brain consists of 100 billion nerve cells with trillions of connections. Seizures may arise in a small area of the brain but then, through these many connections, spread to other areas and eventually to the entire brain.
Epilepsy surgery works by identifying the main area from which seizures arise and removing that area (provided it is not critical for important functions such as speech and movement). This is termed ‘curative, resective surgery’.
Resective surgery is not always successful because it is not always possible to localise where the seizures arise or, once one area of brain is removed, the seizures start to arise from a different area. Sometimes it is not possible to remove the area from which seizures arise, because it is in an area that is crucial for the brain to function.
The surgeon may then decide instead to cut the connections by which the seizure spreads (termed ‘subpial transection’). This operation is generally far less successful.
What you need to take into consideration
If the seizures arise from multiple brain areas (multifocal seizures) or from the whole brain (generalised seizures), then resective surgery is not usually possible. Instead, operations are used with the aim of improving or lessening the seizures with a much lower chance of stopping the seizures.
The second most common focal epilepsy in adults is frontal lobe epilepsy. The frontal lobes are the largest lobes of the brain and some important functions of the frontal lobes are motor function of the body, including speech and short-term memory and attention. Some areas of the frontal lobes are also not well understood and participate in more complex human behaviour and emotion. Particularly if no lesion is seen on the MRI, surgeries in the frontal lobe often require intracranial EEG electrodes placed onto and/or into the brain. These electrodes are placed in the operating theatre, and people then come to the epilepsy-mentoring unit to get the electrodes connected to the EEG machine and to record the seizures.
FIGURE; right frontal lobe epilepsy, showing multiple deep electrodes placed to find where seizures start. The EEG tracing shows the start of a seizure from the middle deep frontal lobe. The arrow points to where the seizure was recorded.
Figure: left frontal lobe epilepsy. The figure shows a computer reconstruction of a patient’s MRI, with the left frontal lobe outlined. On the right hand side the same brain is shown after a grid of electrodes has been placed onto the brain to determine seizure onset and important functions.
A life without seizures can take some adjustment, not only for the individual but also those around them. Families and individuals undergoing the surgery may need additional support to adjust to this. Medication will continue for at least a period, and there is no guarantee that it will be weaned with success. About 50% of individuals are able to wean medication after surgery if seizure free.
One of the side effects of epilepsy surgery in the temporal lobe may be the weakening of memory. How much this affects the patient depends on many factors including whether there is already significant damage involving the hippocampus and how well the memory was working before surgery. Other people may experience some difficulties finding the right word, or have mood problems after surgery. Understanding who’s most likely to experience these side effects is important, so they can be counselled before they consider surgery. The risks of surgery have to be balanced against the risks of continued uncontrolled seizures.
It is important to realise that brain surgery for epilepsy may not always lead to a complete cure. In fact overall probably only half of all people treated will become completely seizure free. Studies have shown that it also very much depends where seizures arise from and whether there is a clear lesion visible on the brain MRI causing seizures that can be completely removed.
In temporal lobe epilepsy, particularly when there is scarring of the hippocampus, up to two thirds of all people can enjoy seizure freedom after the surgery.
FIGURE showing MRI brain with left hippocampal sclerosis (yellow arrow). The hippocampus looks smaller on the left and also brighter compared to the right side.