Imaging of the brain is a major component of the preoperative evaluation of patients who are potential candidates for epilepsy surgery. One factor that determines whether a patient is an appropriate candidate for surgery is whether the lesion responsible for the seizures can be seen on imaging studies such as CT or MRI.
Specialized imaging procedures are used for particular problems such as temporal lobe epilepsy resulting from mesial temporal sclerosis or frontal lobe epilepsy resulting from focal cortical dysplasia.
The neurosurgeon often uses results of the preoperative imaging to assist with intracranial navigation. A computer maps the lesion or abnormal region on the scan and helps guide the surgeon to the exact seizure focus, thus helping to avoid injury to surrounding normal tissue.
Magnetic Resonance Imaging (MRI)
||Mesial temporal sclerosis indicated by arrow
Magnetic resonance imaging (MR imaging, or MRI), uses magnetic fields rather than x-rays to obtain images from deep with the body. Depending on the type of epilepsy, patients may or may not show an abnormality on MRI. Patients with generalized seizures tend to have normal scans, while patients with focal seizures tend to have abnormal findings.
MRI is sensitive to structural abnormalities in the brain. It can detect a vast range of possible abnormalities in patients with epilepsy including:
- Mesial temporal sclerosis
- Scarring related to trauma or infection
- Stroke or bleeding Focal cortical dysplasia or other malformation
For a thorough description of MR imaging, please go to our Magnetic Resonance Imaging page.
Computed Tomography (CT)
Computed tomography (CT; sometimes referred to as a CAT scan) of the head is often performed if a patient is seen in an emergency department. Although less sensitive than MRI, CT can often reveal important details that may be sufficient to obtain diagnosis.
For a thorough description of CT, please go to our Computed Tomography Imaging page.
Positron emission tomography (PET)
|Fluorodeoxyglucose positron emission tomorgraphy (FDG-PET) scan of a normal brain.
Positron emission tomography (PET) imaging involves the intravenous injection of a small amount of a radio-labeled compound, usually glucose (sugar). The brain uses glucose as its primary fuel source. Between seizures, metabolism in the region of seizure focus decreases compared to normal brain regions. On the other hand, if the patient experiences a seizure at the time of the PET study, then the seizure focus usually shows abnormally increased metabolism, which can also help identify the location of seizure activity. PET imaging for epilepsy is usually used as a tool for possible surgical candidates.
Other Imaging Techniques
Other imaging techniques include single-photon emission computed tomography (SPECT) and magnetoencephalography (MEG). Ictal SPECT is a nuclear medicine test that studies changes in blood flow (brain perfusion) that can occur during an epileptic seizure. Blood flow increases in the region of the brain where seizures originate. Intravenous injection of a contrast agent at the time of the seizure can help visualize the region. Magnetoencephalography (MEG) measures magnetic fields generated in the brain. Although Barrow does not currently use this technology, the hospital hopes to acquire it in the near future.