Surgical assessment process
To identify which patients are suitable for surgery, each patient will undergo an intensive assessment process. Tests may include an EEG, a detailed brain scan, video telemetry (involving a week long stay in hospital) and assessment by a psychologist and psychiatrist. Find out more about the tests and investigations we carry out.
The epilepsy surgery team meet to discuss the assessment results of patients every fortnight. You will be offered an appointment with the consultant and depending on the test results, the options will be:
Surgery is not a suitable option
Surgery can be considered
Further tests are required
Outlined below are some of the tests that the epilepsy surgery team may need to perform during your assessment for surgery.
These are used less commonly, and not all patients will require them.
FMRI (functional magnetic resonance imaging)
Patients usually undergo this as an outpatient. This procedure is a modified MRI Scan. FMRI can produce images of areas of the brain that are 'activated' while you are carrying out a specific task. These areas of activation are linked to increased blood flow in those areas of the brain. This helps us identify which areas are involved in functions, such as speech and movement, so we can understand how surgery may affect these functions.
An FMRI scan is carried out while you perform a task and again while you are at rest. The procedure will be explained to you before you go into the scanner and the staff will give you instructions during the scan through an intercom.
For example, to determine the area related to hand movement, you will be asked to tap the fingers of one hand for about 10 seconds, then lie still for the next 10 seconds, and then tap your fingers again for the next 10 seconds. This pattern will be repeated several times during the scan. It is very important to keep very still throughout the whole scan. There may be other tasks you are asked to perform, to help us locate the areas related to language and memory.
The sodium amytal (WADA) test
It is very important for us to know where the speech and memory areas are in your brain, so that we can understand how surgery may affect these functions. Occasionally, we do not obtain enough information from the initial tests carried out by the neuropsychologist, and we may need to perform a more invasive test.
This involves using a short acting drug (sodium amytal) to put one side of the brain to sleep at a time. This allows the neuropsychologist to test the function of each side of the brain separately. You will be awake during the procedure and the effects of the drug only last for 5 to 10 minutes. The medication is injected into the vessels of the brain via a tube that has been inserted up to your neck from the artery at the top of your right leg. This is done under local anaesthetic.You will also have an EEG performed at the same time to monitor your brain activity. Once the sodium amytal has been injected, the neuropsychologist will show you objects and pictures and ask you questions to determine how well your language function and memory are working with half your brain asleep. Once the test is finished you will return to the ward. You may stay overnight in hospital for observation and go home the following day.
EEG and video telemetry recordings use electrodes attached to the surface of the scalp. For most people this provides sufficient information. Occasionally, it is not possible to determine the exact location of the epileptic discharge using scalp electrodes. In this situation, the surgeon may have to insert special electrodes to lie on the surface of the brain, or place the electrodes into the brain tissue itself.
This is only necessary in a small number of people. It will involve an operation to insert the electrodes, and you will require a day or two to recover from the operation before we start recording. The recording will be similar to the video telemetry you will already have had. The electrodes will be attached to the equipment as before, and you will be able to move around the bed space as normal. The surgeon will have stitched the electrodes securely during the operation and your head will remain bandaged during the recording to ensure a good connection and to prevent infection. The recording will take several days, and once completed, you will return to theatre within the next few days to have the electrodes removed.
If the decision has been made that epilepsy surgery would be a good choice for you, this will be carried out at the same time as removing the electrodes.