Epilepsy affects over 95, 000 Ontarians (80, 000 adults; 15, 000 children) and approximately 30% of those are deemed to be medically refractory, that is, they do not respond to treatment with two or more appropriately chosen anti-seizure medications within a reasonable period of time (Ontario Brain Institute, 2015).
Any patient (regardless of age) who fulfills the above criteria for medically-refractory epilepsy is considered a surgical candidate and is eligible for assessment. These patients should be referred to a District Epilepsy Center (DEC) or a Regional Epilepsy Surgery Centre (RESC) in order to assess surgical candidacy. Recent epilepsy service investments by the Ministry of Health and Long-Term Care have increased access to treatment to improve outcomes for this patient cohort (Provincial Guidelines for Epilepsy Surgery Referrals in Ontario, CCSO, 2016).
There are three Regional Epilepsy Centers in Ontario University Health Network (Toronto Western Hospital), London Health Sciences Centre and the Hospital for Sick Children. These are facilities that house a comprehensive epilepsy program that provides all epilepsy clinical services including the assessment by an epileptologist, an Epilepsy Monitoring Unit, neuropsychological services and the ability to perform intracranial monitoring and epilepsy surgery
Although these facilities are available to perform epilepsy surgery, this service remains largely underutilized. The decision to have epilepsy surgery is obviously one that should be given careful consideration but it is also true that many are not aware that surgery is a treatment option or are plagued with myths and misconceptions about risks vs benefits. Others may not even be aware of the existence of these Regional Epilepsy Centres and the work they do.
If you have been told you have medically refractory epilepsy and have tried many anti-seizure medications with no success, speak to your doctor about referring you to a comprehensive epilepsy program where you can be assessed for surgical candidacy.
If you have been told that you are a surgical candidate but have questions, Epilepsy Toronto is here to assist you. We will provide you with information on the various surgical options, help you weigh risks vs benefits, and guide you through your decision-making process. We also have a Surgery Support Group which brings together people with epilepsy who are considering surgery, with those who have done surgery, to learn from their experiences. To join this group, please speak with your Epilepsy Toronto counsellor or complete an intake form to be connected with one.
How does surgery work?
Although epilepsy surgery is complex, the treating team of neurologists and neurosurgeons follow a straightforward set of principles. The strategy is to identify the area of abnormally discharging neurons (the “seizure focus”) and to remove it when possible. In certain patients without a well defined epilepsy focus, surgery can sometimes help, by disconnecting or isolating the abnormal area so that seizures no longer spread to the neighbouring normal brain.
Which patients are candidates for epilepsy surgery?
Only patients whose seizures are not well controlled on medical treatment are considered for surgery. Before seizures are considered medically intractable, the physicians must ensure that the correct seizure diagnosis has been made and that the correct drugs have been used in the appropriate amounts. Even then, however, there is no clear definition of when to move to surgery. Among the factors to consider are seizure type, frequency and severity, the length of time since the diagnosis and the impact of the epilepsy on the patient’s quality of life. There are also other reasons to consider surgical therapy. For instance, repeated seizures may lead to neurological deterioration and certain patients may have intolerable side effects to anticonvulsant medications.
It is important to stress that not all patients with medically refractory epilepsy can be helped with surgery. The best surgical candidates have seizures arising from a single location and from an area of the brain that is relatively silent meaning that the seizure focus can be safely and completely removed.
Which patients cannot be helped by epilepsy surgery?
What investigations are required for surgery?
Patients considered for surgery must be well motivated to undergo the extensive series of tests required to localize the seizure focus and determine whether it can be safely surgically removed. A neurological history and physical examination is the first step in evaluating a patient with seizures. This gives important clues into the many causes of the seizures and can identify the part of the brain from which the seizures are likely to be originating. Next, imaging the brain is important to identify any abnormalities which may cause seizures. The findings of the imaging studies may show a lesion or may show subtle abnormalities such as an area of the brain involved in the seizure which is slightly smaller than usual.
What is the neuropsychological assessment for surgery?
An important aspect of the evaluation is the neuropsychological assessment. These tests document the consequences of the seizures on brain function. Since each part of the brain subserves a specific function, each identified neuropsychological finding can be matched to precise brain areas to give important clues about seizure localization. In addition, as a preoperative tool, neuropsychological tests can identify which hemisphere is dominant for speech and memory and can, by predicting the neurological consequences of the proposed operation, help in the safety of the surgery. It is interesting that after successful operations, the neuropsychological tests often document improvements in brain function associated with improved seizure control.
How is the surgery performed?
After collection of the necessary data a decision regarding surgery is made. The largest group of surgical candidates are patients with seizures that have a single seizure focus. Operations can be done under general anaesthesia but when seizures arise near areas of the brain involved in important functions such as speech, motor control or sensations, many epilepsy operations are performed under local anaesthesia with the patient awake and fully cooperative. The surgical team performs an EEG in the operating room and stimulates the brain electrically to establish the relation between the seizure focus and essential brain areas. This technique gives the surgeon a detailed account of where the seizures are originating and tells when it is safe to proceed with the resection and when it is necessary to back-off. Operating with the patients awake, thus increases the safety of the surgery and increases the chances of removing the neurons responsible for the seizures when it might otherwise be considered to be too dangerous.
What is the “callosotomy” surgery for epilepsy?
Another surgical technique used is that of disconnecting the seizure focus from the normal brain. The best example of this is an operation called a “callosotomy”. This operation done in patents with generalized seizures, interrupts the connections from one half of the brain to the other. The end result is that seizures no longer spread from the epileptic to the more normal half of the brain. This operation does not cure the patients of epilepsy but can help with the frequency and severity of attacks. It is particularly effective for patients with “drop attacks”. These are seizures characterized by sudden failing and without any warning.
What are the risks and benefits of epilepsy surgery?
As with any operation, there are risks to surgery for epilepsy. The risks depend on the area being operated and are those of producing a disturbance in motor strength, in sensation, in vision or speech. There have also been rare cases of surgical mortality. Fortunately, with continuing refinement in neurosurgery, the chances of long lasting complications are small at approximately two per cent.
In patients with an identified focal seizure focus, the success rate of surgery is up to 80 per cent. This is the number of patients that will be seizure free for five years after surgery with some patients experiencing occasional auras and some still taking anticonvulsant medication. For patients with generalized seizures without a focal onset the results are still not as good. These patients may nevertheless obtain a worthwhile improvement with an operation.
Have there been recent advances in epilepsy surgery?
There is an increasing awareness of the benefits of surgery in the treatment of certain patients who continue to have seizures despite of the best treatment with anticonvulsants. The last decade has seen significant advances in the surgical treatment of epilepsy. This has come about with the development of better imaging techniques such as magnetic resonance imaging (MRI) and better seizure localization with increasing sophistication of electroencephalographic (EEG) technology, single photon emission computed tomography (SPECT) and positron emission tomography (PET).
These advances together with improvements in surgical techniques have increased the safety and efficacy of operations for the treatment of epilepsy.