FDG-PET in Epilepsy

FDG-PET measures regional brain glucose metabolism using the radiotracer fluorodeoxyglucose. In drug-resistant focal epilepsy, it is primarily used during presurgical evaluation to identify abnormal metabolic networks that may help lateralise or localise the epileptogenic region.

What FDG-PET measures

FDG behaves similarly to glucose and is taken up by metabolically active tissue.

The resulting scan shows relative patterns of glucose metabolism across the brain.

Interictal PET

Epilepsy FDG-PET is usually acquired between seizures.

The region associated with the seizure network often shows hypometabolism, meaning reduced glucose uptake compared with surrounding or contralateral brain.

Why PET can be broader than the seizure-onset zone

Hypometabolism may extend beyond the cortex where seizures actually begin.

It can reflect the wider epileptic network, chronic functional disturbance, medication effects or remote connected regions.

When PET is most useful

PET is especially useful when MRI is negative, subtle or discordant with EEG and seizure semiology.

It can also help determine which of several abnormalities is most likely to be clinically relevant.

Temporal lobe epilepsy

Unilateral temporal hypometabolism can support lateralisation in temporal lobe epilepsy.

However, PET is not a substitute for seizure semiology, EEG or MRI.

Extratemporal epilepsy

PET can help identify subtle focal cortical dysplasia and other extratemporal epileptogenic regions, although localisation may be less straightforward than in classic temporal patterns.

PET–MRI co-registration

Coregistering PET to the patient’s structural MRI allows metabolic abnormalities to be mapped onto anatomy more precisely.

This can improve detection of subtle lesions and guide surgical or invasive-EEG planning.

PET/MRI scanners

Some centres acquire PET and MRI simultaneously.

Others perform separate scans and fuse them computationally; both approaches can be clinically useful.

What the evidence shows

A 2024 review described interictal FDG-PET as an established presurgical test, particularly in MRI-negative or discordant focal epilepsy.

A 2024 systematic review and meta-analysis also examined the relationship between localising hypometabolism and surgical outcome.

Seizures near the injection

A seizure occurring shortly before or during tracer uptake can alter the metabolic pattern.

Accurate documentation of seizure timing is therefore important for interpretation.

Radiation

FDG-PET involves ionising radiation.

Use in children and repeated scanning requires careful justification, although modern protocols aim to minimise dose.

Limitations

Hypometabolism is not specific for epilepsy and can occur with structural lesions, previous injury and other neurological disorders.

Normal PET does not exclude focal epilepsy.

PET does not directly show the epileptogenic zone

The epileptogenic zone is the minimum cortex that must be treated to achieve seizure freedom.

PET contributes evidence about that network but cannot define it by itself.

Worldwide access

PET requires a nuclear-medicine service, radiotracer supply and specialist image analysis.

Access is therefore far more limited globally than MRI or routine EEG.

The central point

FDG-PET is a metabolic map, not a direct seizure recording. Its greatest value is in difficult focal epilepsy where it adds another independent line of localisation evidence.

Sources

Evidence checked: September 2026.