Epilepsy surgery · Lobeworks/17

Epilepsy surgery removes, destroys or disconnects the part of the brain where seizures start, and it is the treatment most likely to stop seizures altogether in a person whose focal epilepsy has resisted medication.

Epilepsy surgery. Epilepsy surgery removes, destroys or disconnects the part of the brain where seizures start, and it is the treatment most likely to stop seizures altogether in a person whose focal epilepsy has resisted medication.

It is considered once epilepsy is drug-resistant, which by the international definition means that two tolerated, appropriately chosen and used medicines have failed to give lasting seizure freedom; about a fifth to a third of people with epilepsy reach that point. Surgery then depends on two questions answered before any operation: where exactly the seizures start, and what that tissue does. Video-EEG records seizures, MRI looks for a lesion, PET, SPECT and MEG add evidence, and when these disagree electrodes are placed inside the skull for days to catch seizures at their source. Language and memory are mapped so the operation can spare them.

Resection is the classic operation. Removing the front of the temporal lobe with the hippocampus stops seizures in the majority of people with mesial temporal lobe epilepsy; outside the temporal lobe the results are lower.

Smaller procedures are spreading. Laser interstitial thermal therapy heats and destroys a small target through a thin probe under MRI guidance, with less damage to the tissue around it.

Disconnection is used when removal is impossible. Cutting the corpus callosum reduces drop attacks by stopping spread between hemispheres, and disconnecting a whole hemisphere is reserved for severe epilepsy in children whose one hemisphere is already damaged.

When no focus can be removed, implanted stimulators (vagus nerve stimulation, deep brain stimulation or responsive stimulation) are the alternative.

Epilepsy surgery is mostly a problem of localisation.

The operation itself is the short part; the work is proving, from many recordings, that the tissue to be removed is where the seizures begin and is not doing something the person cannot lose.

Questions: How well does removing part of the temporal lobe stop seizures? In the randomised trial that settled the question, 80 people with drug-resistant temporal lobe epilepsy were assigned to surgery or to continued medication, and after one year 58 % of the surgical group were free of seizures that impair awareness against 8 % of the medical group. Surgery is considered once two appropriate, tolerated medicines have failed to give lasting freedom from seizures, the international definition of drug resistance. The risks, chiefly to memory and to part of the upper visual field on the side opposite the operation, are weighed with mapping of language and memory before the operation. When do doctors implant a responsive stimulator instead of removing the seizure focus? Removal is preferred when it is safe, because it can stop seizures altogether. A stimulator is chosen when the focus lies in tissue that cannot be spared, such as cortex that controls language or movement, or when seizures start in both hippocampi, where removing both would destroy the ability to form new memories. Responsive stimulation rarely ends seizures entirely, but its effect grows over the years, reaching a median reduction of 75 % after nine years in the long-term study.