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What is Epilepsy surgery?

Epilepsy surgery

If anti-epileptic medications do not control epilepsy seizures, brain surgery can be considered for some patients.

The most commonly performed type of brain surgery is called Resective Brain Surgery. Resective surgery for epilepsy is used to remove the part of the brain that is causing the seizures.  This means that it can only be used for people where the seizures start in one area of the brain. When seizures start in one part of the brain only, this is called Focal Epilepsy.

There are different kinds of Resective Brain Surgery that occur in different parts of the brain, depending on where the seizures start. Some surgeries mainly involve removing a lesion as seen on the MRI – this is called a lesionectomy. Other surgeries involve larger parts of the brain. They may involve all or most of one of the lobes of the brain. The brain is divided into four paired sections:

  1. The frontal
  2. Parietal
  3. Occipital
  4. Temporal lobes

Temporal lobe surgery

The most common type of Resective Brain Surgery in adult epilepsy is performed in the temporal lobe. The temporal lobe is located on either side of the brain just above the ear. It plays an important role in language, hearing and memory, and many people with temporal lobe epilepsy therefore also suffer particularly from memory problems.

A temporal lobe resection means that brain tissue in the temporal lobe is cut away, to remove the seizure focus. The anterior (front) part of the temporal lobe and the deep part and mesial (deep middle) portions of the temporal lobe are the areas most often involved. The deep portions contain a structure called the hippocampus, which is involved in forming memories.

A temporal lobe resection requires exposing an area of the brain using a procedure called a craniotomy. After the patient is put to sleep with anaesthesia, the surgeon makes an incision in the scalp, removes a piece of bone and pulls back a section of the dura, the tough membrane that covers the brain. This creates an opening in which the surgeon inserts special instruments for removing the brain tissue. Surgical microscopes are also used to give the surgeon a magnified view of the area of the brain involved. The surgeon utilises information gathered during the pre-operative evaluation – as well as during surgery – to define, or map out, the route to the correct area of the temporal lobe. After the brain tissue is removed, the dura and bone are fixed back into place, and the scalp is sutured up using stitches or staples.

Other surgical procedures

Another area of surgical intervention is implantation of brain stimulators. Stimulators introduced into the brain are currently being investigated. In general, they can be considered in people where there are no resective surgery options.  Deep Brain Stimulation  (DBS) is a surgical procedure by which leads that have been implanted into specifically targeted areas in the brain deliver controlled electrical stimulation. This procedure may, in selected people, ameliorate seizures.

Much more widely used are Vagal Nerve Stimulators. These are small devices, similar to a cardiac pacemaker, which are implanted under the skin below the left collarbone. This is connected via a lead to the vagus nerve in the left side of the neck. The VNS stimulates the vagus nerve at intervals to reduce the frequency and intensity of seizures.

Now that we clarified what is epilepsy surgery, we will consider how it works.

How does epilepsy surgery works?

Epilepsy surgery can work in 3 different ways:

  1. By removing the ‘bad’ part of the brain
  2. Removing the connection of the ‘bad’ part to the other brain areas
  3. 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.

So, how does 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. Indeed, 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, the area from which seizures arise is impossible to remove, 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 kind of  epilepsy surgery is generally far less successful.

Side Effects

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. For example, 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. Consequently, counselling is recommanded before considering surgey. 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.

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.

Post-surgery

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.

 

Find out more about the e-pilepsy project here.