If your seizure medicines are not working well and a CT scan or MRI shows that you have a tumor, an abnormal collection of blood vessels, or some other "lesion" in your brain that is a likely cause of your seizures, surgery may be a good option. The neurologist or epileptologist will refer you to a neurosurgeon, who will investigate further to plan the safest and most effective surgery for you. An important part of this planning is deciding how large an area to remove.

Your seizures may start in an area of your brain that is near the lesion but not part of it. The neurosurgeon will need to figure out whether just removing the lesion itself (called a lesionectomy) will be enough to stop your seizures. If your seizures begin outside of the lesion, the surgery may need to include a larger area. For lesions in the temporal lobe, this means that your surgery will be more like a temporal lobectomy, the most common kind of epilepsy surgery for people who do not have visible lesions.

Both kinds of surgery can be effective in stopping seizures. Which will work best for you depends on the type of lesion and other factors. Patients with small, low-grade tumors, cavernous hemangiomas (a type of benign tumor mostly composed of dilated blood vessels), and other blood-vessel malformations are the most likely to be successfully treated with lesionectomy alone. About 50% to 90% of such patients have been seizure-free after removal of only the lesion, as shown by an image like an MRI.

Neurosurgeons often report better results after removal of a larger area of the brain, however. They study EEGs to look for electrical abnormalities outside the boundaries of the lesion. In the temporal lobe, one area that is often found to be abnormal is the brain structure called the hippocampus. If your lesion is close to the hippocampus or if your seizures began when you were very young, it's likely that an examination would show that many cells have been lost. Cell loss from the hippocampus is regarded as a sign that seizures begin there or at least in that area. Sometimes seizure activity arises from the hippocampus and the amygdala (a neighboring structure) even if the lesion is not nearby. When this happens, removing only the lesion will not stop the seizures.

The danger in removing a larger area of your brain is that the surgery may impair functions such as language and memory. If the neurosurgeon is considering removal of more than just the lesion, you should first undergo careful mapping of the functional regions in the brain. You probably will have Wada testing to find out which side of your brain is dominant for language and to see whether the side opposite the lesion has adequate memory function. If the lesion is in the dominant temporal lobe, subdural grid electrodes may be used to record seizures and map regions of language function. This information can be used to plan the surgery. Some surgeons prefer instead to perform the operation while you are awake so they can map language during the procedure.