EPILEPSY in the 21st CENTURY:
The Future of Epilepsy Brain Surgery

Today, people with temporal lobe epilepsy form the largest group of surgery patients. This type of epilepsy often comes from damage to structures that lie deep in the temporal lobe of the brain— structures called the hippocampus (where memory "resides") and the amygdala. Surgeons treating temporal lobe epilepsy open up the head and cut out or "resect" the "epileptic" parts of the brain, such as the outer layer of the temporal lobe, and/or the hippocampus and amygdala. Between 62 and 66% of these resection patients have favourable outcomes. The goal of surgery in the future is to reduce its side effects-such as transient or permanent speech and memory problems- as well as its discomfort, invasiveness, and the length of the hospital stay and recovery required.

A new type of surgery called "stereotactic" surgery ues a frame attached to the outside of the head to hold the head in place. An MRI scan pinpoints the affected area of the brain to within 1 millimeter. A two­inch cut is sliced just above the ear, and a hole the size of a quarter is made in the head. Through the hole is placed an electrode or probe which is heated up, and an area of the brain is cauterized or lesioned.

People who have had stereotactic surgery appear to recover sooner than patients having temporal lobe resections; they can go back to work after 10 days or two weeks. Their language seems less disturbed, although their memory problems are about the same, probably because the hippocampus is still targeted as the source of the epilepsy. Nine months later, the MRI scan shows that the area has been hollowed out by the cauterization. Of the approximately 20 patients who have had this procedure so far at Dr. Parrent's hospital in London, 60% had a successful outcome.

Radiosurgery is another promising surgical technique of the future. This technique works by concentrating radiation on the epileptic tissue in the brain, without cutting open the head to do so. The radiation can be done either by using a "Linear Accelerator Device," or a "Gamma Knife."

In Gamma Knife radiosurgery, a frame is attached to the head (much like stereotactic surgery), and radiation is projected onto the hippocampus and amygdala of the temporal lobe. After this procedure is completed, the person goes home, and their seizures continue unchanged. But gradually, over time, their seizures apparently improve. After about nine months, their seizures cease (at least they did in the 21 research subjects having this new procedure). MRI scans show changes in the patient's brain that progress and then resolve, so that the brain ends up being substantially the same as it was before the surgery.

"You are left with a person who is seizure-free with an MRI scan that shows nothing has substantially changed inside. But does this structure that has been radiated and no longer produces seizures still function in its normal role of maintaining memory?" asks Dr. Parrent. "Should this be the case, it offers an amazing therapy of removing the bad part of how that brain functions and leaving its normal functions intact."

Dr. Parrent warned that we don't yet know whether this is the case, as detailed memory testing still needs to be done on the patients who have had radiosurgery. Such testing will be very important in influencing whether this technique replaces some of the other techniques we use to treat temporal lobe epilepsy. And what about the risks from radiation itself? The surgeon radiates a very small area to reduce the risk of radiation damage, but we may not know the long-term effects on patients until 15-20 years later.

What new surgeries does the future have to offer the person with generalized epilepsy, whose whole brain is involved in their seizures?

Thalamic stimulation is currently undergoing a multi­centred trial. A stimulator wire with some exposed electrodes at the end is placed deep into a key part of the brain called the thalamus. The wire is attached to a pacemaker implanted in the chest below the collarbone, much like a cardiac pacemaker, and this device sends electrical impulses into the thalamus. Tentative results so far indicate that thalamic stimulation appears to have a beneficial affect on generalized tonic­clonic and partial motor seizures, but not on other types. It has not proven to be a cure­all.

What is on the horizon? Researchers are investigating complex therapies such as transplantation of animal fetal brain cell tissue into human brains to reduce seizures. In mouse and rat models, it apparently can reduce seizures in genetic epilepsies. However, we must first identify the tissue into which it should be transplanted. Transplanting hippocampus tissue from fetal animals into a lesioned human hippocampus appears to improve epilepsy. However, it may take another decade before this treatment is developed.

Deep Brain Stimulation may be an effective surgical procedure, and will be hotly pursued. It involves stimulation of the sub­thalamic nucleus and basal ganglia, areas which are not usually associated with epilepsy.