Epilepsy surgery is a useful and safe treatment for patients with drug-resistant focal epilepsy. However, although it has been shown to significantly improve the quality of life of patients, it is an underutilized treatment strategy. One of the reasons for this “underutilization” is the fear of the consequences of open neurosurgery. In recent years, different techniques have been developed which, through minimally invasive procedures, can be used as an alternative to open surgery in selected patients. Some of these techniques are:
Radiofrequency thermocoagulation guided by stereo-electroencephalography (E-EEG):
Thermocoagulation or thermoablation with intracerebral electrodes, due to its efficacy and safety, has become one of the main minimally invasive treatment options for patients with focal epilepsy in European and American reference centers. It consists of the implantation of electrodes deep in the brain that allow delimiting the epileptogenic zone (brain area where epileptic seizures are generated) by means of an electroencephalogram recording. Once the area where the seizures originate has been identified, thanks to the application of thermal energy, a small lesion can be produced in the selected area and thus prevent the seizures from occurring. 
About 50% of patients who undergo this treatment have a significant improvement in seizure frequency, and about 40-50% of patients with well-demarcated focal lesions may be free of seizures after the procedure. The initial response to thermocoagulation predicts a good outcome if resective surgery is subsequently performed. The complication rate is very low and depends largely on the experience of the neurology-neurosurgery team performing the procedure. In addition, no anesthesia is required to perform the ablation, which allows the efficacy and safety of the treatment to be monitored “in real time”.
Gamma Knife (GK) radiosurgery:
Radiosurgery with stereotaxy consists in the lesion with gamma radiation of a circumscribed area of the brain. There are multiple indications for the application of Gamma Knife, among them, the most studied are epilepsy secondary to hypothalamic hamartomas or for patients with hippocampal sclerosis who do not wish to undergo open surgery. 
is also useful in other types of lesions, such as focal cortical dysplasias, especially if they are located in areas “at risk” for open surgery. Its main disadvantage is that the effect on seizure control may take 12 to 24 months to appear, but it is a safe, painless technique that does not require hospitalization to be performed, so the patient can go home the same day it is performed.
Laser thermoablation
It is a technique similar to thermocoagulation in which a single electrode is inserted in the area that produces epileptic seizures and thermal energy is applied to injure that tissue. Compared to the two previous techniques, laser thermoablation still has little experience and scientific evidence. It has the advantage of allowing the monitoring of the process with magnetic resonance imaging, although it has the disadvantage of not allowing an electrical recording in the implanted electrode. This makes it an option for patients with small and well-delimited brain lesions.
Other techniques: Vagus Nerve Stimulation, RNS (“Responsive-Neurostimulation”) and Trigeminal Stimulator.
While the previous techniques are curative techniques, these are “palliative” techniques, since they are based on the implantation of devices 
which detect the onset of seizures and, by applying an electrical stimulus, prevent their propagation. The most commonly used is the vagus nerve stimulator (image), which is mainly used for patients with violent seizures at risk of falling. The second, less commonly used, implants a generator in the skull which, by means of electrodes, sends electrical pulses to a specific area of the brain at the moment when the seizure is beginning to occur. Trigeminal stimulation is an option which, although it has not shown significant efficacy in seizure control, does seem to improve the quality of life of patients who use it.
Deep brain stimulation
It consists of radiofrequency stimulation of electrodes implanted with stereotaxy in the deep brain nuclei (thalamus nuclei). Although its efficacy in terms of seizure control is modest, there are studies that support its efficacy in patients with generalized epilepsies that do not respond to medical treatment.
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AUTHORS:
Dr. Carla Anciones and Dr. Ángel Aledo
Epilepsy Program, Hospital Ruber Internacional, Madrid.
