What is epilepsy surgery?
Epilepsy surgery is a neurosurgical procedure to prevent or reduce the occurrence of epileptic seizures. Epilepsy surgery involves removal or surgical alteration of the part of the brain from which epileptic seizures originate.
Epileptic seizures are caused by sudden abnormal bursts of electrical activity in some brain cells, which may then spread to other parts of the brain. Epilepsy surgeries are performed to remove brain tissue where abnormal electrical pulses begin, or disrupt the pathways by which they travel.
Why is an epilepsy surgery performed?
Long-term control of epileptic seizures is important for a patient’s wellbeing because uncontrolled seizures can be debilitating and increase the risk for:
- Accidental injuries
- Cognitive decline
- Status epilepticus, an emergency condition of continuous seizure that lasts longer than five minutes
- Sudden unexplained death in epilepsy (SUDEP)
- Psychological, social and vocational impairment leading to anxiety and depression
Who is a candidate for epilepsy surgery?
Antiepileptic drugs are the mainstay treatment for epilepsy. Candidates for epilepsy surgery must satisfy certain criteria which include:
- Antiepileptic drugs do not control seizures effectively or patients are unable to tolerate the side effects of antiepileptic drugs
- Seizures always arise from the same point of origin (focal epilepsy)
- Quality of life can be significantly improved with surgery
Surgical options are limited if the focal seizure area controls critical functions such as
- Speech
- Vision
- Memory
- Movement
- Sensation
What are the types of epilepsy surgery?
The type of epilepsy surgery depends on the type of seizures and where they originate. Types of epilepsy surgery include:
Invasive surgeries
Invasive surgeries involve cutting open the skull to access the brain in a procedure known as craniotomy.
- Focal resection: Surgical removal of brain tissue which is the origin of seizures. The largest part of the brain, the cerebrum, is divided into two halves (right and left hemispheres). Each hemisphere consists of four sections; frontal, temporal, parietal and occipital lobes. The temporal lobe is the seizure focus for a majority of patients with focal seizures. Focal resection may be of two types:
- Anteromedial temporal resection (AMTR): Removal of anterior temporal lobe, the most frequently performed epilepsy surgery.
- Extratemporal resection: Removal of brain tissue from any of the three lobes other than the temporal lobe.
- Lesionectomy: Removal of brain lesions that cause focal seizures.
- Corpus callosotomy: Corpus callosotomy involves severing corpus callosum, a band of nerve fibers that connects the two cerebral hemispheres. Corpus callosotomy prevents communication between the two halves of the brain and is performed in patients who have generalized seizures affecting both hemispheres.
- Functional hemispherectomy: Hemispherectomy means the removal of an entire brain hemisphere. In functional hemispherectomy (also known as hemispherotomy), doctors remove as little of the brain tissue as possible, but disconnect the hemisphere’s communication with the rest of the brain.
- Multiple subpial transection (MST): MST involves making fine shallow cuts (transections) in the brain tissue to prevent the flow of seizure impulses. This procedure is used for focal seizures in parts of the brain which have critical functions and are not safe to remove.
- Neurostimulation: Neurostimulation is a procedure to deliver low-voltage electrical impulses to a nerve or the brain, using a set of implanted electrodes and a battery-operated device that generates the electrical impulse. The mild electric current interrupts the brain’s electrical communication and prevents the flow of seizure impulses.
- There are three types of neurostimulation:
- Vagus nerve stimulation (VNS): The stimulating device is implanted under the skin in the chest to deliver electric pulses to the vagus nerve, through electrodes implanted near the neck. Vagus nerve is a major communication link between the brain and other internal organs.
- Responsive neurostimulation device (RNS): The stimulator is implanted under the scalp with leads connecting to electrodes on the surface of the brain’s seizure focus region.
- Deep brain stimulation: Electrodes are implanted deep in parts of the brain such as amygdala or hippocampus. The stimulating device is placed under the skin in the upper chest.
- There are three types of neurostimulation:
Minimally invasive procedures
Stereotactic radiosurgery: A procedure that delivers precisely focused beams of radiation using 3D imaging, to destroy brain tissue in the seizure focus area.
Laser interstitial thermal therapy (LITT): A procedure that uses a laser to eliminate the seizure-causing tissue. This method is useful for people with focal seizures caused by clearly defined small brain lesions. LITT is under clinical trials for safety and efficacy in patients with seizures associated with mesial temporal sclerosis.
How successful is surgery for epilepsy?
The success of the epilepsy surgery depends on the type of surgery. Patients will usually have to continue taking antiepileptic drugs for at least a year or more. Following are the surgical outcomes as revealed by studies on the efficacy of epilepsy surgery.
- Focal resections: People who underwent temporal resection had better outcomes than those who had extratemporal resection. In a randomized trial 52% patients remained seizure-free for five years, apart from simple partial seizures.
- Corpus callosotomy: Corpus callosotomy generally reduces the frequency and intensity of seizures but does not stop them. Approximately 60% to 70% reduction can be expected in more than 80% of patients. Up to 15% may have no worthwhile benefit.
- Multiple subpial transection: Outcome with this type of surgery is not entirely clear because many of the patients also have a resection. Some studies have shown complete seizure control in approximately 55% of patients with no significant deficits in neurological functions.
- Functional hemispherectomy: Functional hemispherectomy had a seizure free outcome of 54% to 90% depending on the type of epilepsy syndrome treated. There was a significant improvement, which included nondisabling seizures, in 80% to 90% patients.