Educational scope notice: This is a study note for medical students, not medical advice, diagnosis, or treatment guidance. Clinical management should follow local protocols and current guidelines.
Nuclear imaging in epilepsy exists for one clinical situation: drug-resistant epilepsy facing possible surgery. About one-third of patients never reach seizure control with medication, and resistance is declared only after careful years-long work: at least two drugs tried as monotherapy, then combinations, each change requiring a taper, an overlap, and time to judge effect. For these patients surgery is the realistic chance of cure, but the surgeon must know exactly where seizures start.
Neither routine tool answers that question alone. EEG captures seizure timing exquisitely but localizes crudely, partly because activity from one mesial temporal lobe reflects almost instantly to the other, defeating lateralization. MRI shows structure yet is normal in about one-third of drug-resistant patients. Functional imaging fills the spatial gap: interictal FDG-PET shows where glucose metabolism has fallen around the focus, and ictal SPECT captures hyperperfusion at the seizure onset at the moment of firing.
| Technique | State | What it shows | Clinical role |
|---|---|---|---|
| Interictal FDG-PET | Seizure-free during 30 to 45 min uptake | Hypometabolism around the focus | Lateralization, MRI-negative localization, bilateral disease detection |
| Ictal SPECT | Tracer injected during the seizure | Hyperperfusion at seizure onset | Focal localization when PET is non-diagnostic |
PET is the workhorse because it is available and well validated; ictal SPECT is conceptually powerful but logistically demanding, requiring tracer injection at the exact moment of a seizure in a monitored unit. Three principles govern both: EEG monitoring during FDG uptake must confirm the patient stayed seizure-free or the scan is contaminated, a high-quality MRI is always required for anatomical interpretation, and remote hypometabolism beyond the focus warns that surgery may work less well.
Choose a route through the topic
- Nuclear Imaging of Epilepsy, FDG-PET explains the interictal hypometabolism signal and its uptake protocol, temporal lobe lateralization, bilateral disease as a surgical stop sign, MRI-negative localization, PET-MRI coregistration, and the reduced sensitivity outside the temporal lobe.
- Nuclear Imaging of Epilepsy, SPECT explains the ictal hyperperfusion concept, injection timing, and how SPECT complements PET when interictal imaging does not localize.
This hub belongs to the epilepsy family: start at the Epilepsy hub for definitions and the overall map, then come here when the question turns surgical. The PET and SPECT platforms also appear in dementia and movement-disorder workups, but here the question is purely spatial: where does the seizure start, and can it be removed.
Evidence anchors
- NICE. Epilepsies in children, young people and adults (NG217): https://www.nice.org.uk/guidance/ng217