Trevor Resnick, MD: Stereo EEG [electroencephalography] is a technique of frameless insertion of depth electrodes into the brain and doing it using 3-dimensional information. Previously, we did put depth electrodes into the brain but [we used] a frame. And this is an easier way to do it, and it is a technique with a morbidity rate that is lower. About 1% of patients may have an area of bleeding or infection in relationship to the insertion of the stereo EEG. So it is an added technical advance in terms of helping us localize where seizures are coming from. Now, it’s not the whole answer, but it’s definitely part of the answer that has helped us with localization.
One of the problems in finding an area where the seizures are coming from is putting your recording equipment in an area where you think the seizures are coming from. What we’ve done over the years is used grids, [putting] a grid of electrodes over the surface of the brain. And that’s very good for evaluating a spread pattern when you’re looking at seizures that are over the surface of the brain. But the brain has infoldings. They are gyri and sulci, and if the origin of the seizure is at the depth of the sulcus, having grid electrodes is not going to give you that information. It’s very good to think of using SEEG, or stereo EEG, because if you have an idea of where the seizures are coming from, you can put depth electrodes or the stereo electrodes into the depth of the brain, where these deeper gyri are that will give you more information. Often it’s very useful if you have either a lesion that is deep in order to give you better localization data or sometimes using it in combination with grid electrodes, so you can get 3-dimensional information of where seizures are coming from.
It’s really an evaluation technique. So it’s the kind of thing that if you are considering surgery in a patient with epilepsy—if you’re going to be removing an area of tissue that is causing seizures—being able to have SEEG as an additional tool in order to 3-dimensionally evaluate where the seizures are coming from, and the fact that it can be used [in] a robot without a frame, has made that technique much easier to use and has added to our ability to localize the epileptic focus.