Epilepsy Surgery and Presurgical Assessment

Specialist treatment

Epilepsy surgery is not a single operation and it is not reserved only for people with an obvious lesion on MRI. Presurgical assessment asks whether seizures arise from a brain network that can be treated safely and whether surgery offers a better balance of benefit and risk than continued medical treatment alone.

Central point: Referral for epilepsy surgery assessment does not mean someone will have surgery. It means a specialist team will assess whether surgery or another advanced treatment could help.

Who should be referred?

NICE recommends referral to a tertiary epilepsy service for people with drug-resistant epilepsy for consideration of resective surgery, including people whose MRI does not show an obvious abnormality. Referral should not be withheld simply because someone has a learning disability or a genetic diagnosis.

The ILAE has also emphasised timely referral for surgical evaluation once drug resistance is established. Waiting through repeated medication failures can prolong exposure to seizures, injury, psychosocial consequences and epilepsy-related mortality risk.

What does drug-resistant epilepsy mean?

The widely used ILAE definition is failure of two tolerated, appropriately chosen and adequately used antiseizure medication schedules, whether as monotherapy or in combination, to achieve sustained seizure freedom. Drug resistance does not automatically mean surgery is suitable, but it is a major reason to consider tertiary evaluation.

What happens during presurgical assessment?

The assessment combines several kinds of evidence. Long-term video-EEG may be used to record typical seizures and identify where electrical changes begin. MRI is reviewed using epilepsy-specific protocols. Neuropsychological testing examines functions such as memory, language and executive skills and can help estimate the cognitive risks of intervention.

Depending on the case, the team may also use PET, ictal or interictal SPECT, functional MRI, magnetoencephalography, EEG source imaging or ultra-high-field MRI. These tests are not routine for everyone; they are selected when they answer a specific localisation or safety question.

FDG-PET in Epilepsy →
Ictal and Interictal SPECT in Epilepsy →
MEG and Magnetic Source Imaging →
EEG Source Imaging →
Functional MRI for Language and Motor Mapping →
7-Tesla MRI in Epilepsy →

When is intracranial EEG used?

If non-invasive tests do not provide enough certainty, electrodes may sometimes be placed on or within the brain to record seizures more directly. Stereo-EEG uses depth electrodes placed through small skull openings. Intracranial monitoring is invasive and is reserved for carefully selected cases where the information could change treatment.

Types of epilepsy surgery

Resective surgery removes brain tissue judged to be responsible for seizures when this can be done with acceptable risk. Examples include temporal lobe resections and lesionectomy. Other approaches include disconnection procedures, such as corpus callosotomy or hemispheric surgery in selected severe epilepsies, and minimally invasive ablative techniques in some centres and indications.

The best option depends on seizure type, location, underlying cause, age, developmental profile, expected benefits and the functions at risk. Surgery is therefore a multidisciplinary decision rather than a procedure chosen from imaging alone.

How effective can surgery be?

Outcomes vary greatly by epilepsy type and operation. One landmark randomised trial in temporal lobe epilepsy found that surgery produced substantially greater seizure freedom and better quality of life at one year than continued medical therapy in carefully selected people. That result cannot simply be applied to every epilepsy surgery candidate, but it established that surgery can be markedly more effective than prolonged medication-only treatment in an appropriate group.

What are the risks?

Risks depend on the procedure and the area treated. They can include infection, bleeding, neurological deficit, visual field change, memory or language problems, mood changes and the possibility that seizures continue. Presurgical testing is designed partly to reduce these risks by mapping important functions and estimating what can safely be treated.

What if resective surgery is not suitable?

Tertiary assessment can still be useful. Other options may include vagus nerve stimulation, deep brain stimulation, responsive neurostimulation in countries where it is available, ketogenic dietary therapy or additional medication strategies. Referral is therefore broader than a yes-or-no decision about removing brain tissue.

Drug-Resistant Epilepsy · MRI and Neuroimaging · EEG Explained Properly · Vagus Nerve Stimulation

Referral should not wait for years of additional medication trials

Drug-resistant epilepsy is generally recognised after failure of two appropriately chosen and tolerated antiseizure medication schedules to achieve sustained seizure freedom. At that point, referral to a comprehensive epilepsy centre allows assessment of surgical and non-surgical options rather than assuming surgery means immediate brain resection.

Phase 1: non-invasive presurgical evaluation

Core assessment usually combines detailed seizure history and semiology, prolonged video-EEG, dedicated epilepsy MRI and neuropsychological assessment. Depending on the case, PET, SPECT, MEG, EEG source imaging, functional MRI and other specialised tests may be added.

The aim is convergence

No single test defines the epileptogenic zone. Teams look for agreement between clinical seizure features, electrical onset, structural abnormalities, functional imaging and cognitive findings.

MRI-positive and MRI-negative pathways

A visible, concordant lesion can make the surgical hypothesis clearer. MRI-negative epilepsy is more complex but does not automatically exclude surgery. Modern assessment may include expert MRI re-review, post-processing, PET, SPECT, MEG and SEEG.

What recent evidence says about MRI-negative surgery

A 2025 systematic review found that people labelled MRI-negative were less likely to undergo surgery and had lower average favourable postoperative outcomes than MRI-positive groups. Importantly, the same review showed that MRI post-processing can uncover lesions previously missed, reinforcing the need for a modern imaging pathway before accepting the label “MRI-negative”.

Phase 2: invasive evaluation

If non-invasive tests do not provide enough certainty, intracranial EEG may be considered. SEEG is increasingly used because it can sample deep and distributed networks in three dimensions.

Functional risk assessment

Surgery planning must define not only where seizures arise but what that tissue does. Functional MRI, neuropsychology, direct cortical stimulation and, in selected cases, Wada testing can help estimate risks to language, memory, movement and other critical functions.

Explore individual procedures

Corpus Callosotomy →
Hemispherectomy and Hemispherotomy →
Laser Interstitial Thermal Therapy (LITT) →
Lesionectomy for Epilepsy →
Selective Amygdalohippocampectomy →
SEEG-Guided Radiofrequency Thermocoagulation →
Surgery for MRI-Negative Epilepsy →
Anterior Temporal Lobectomy →

Resective procedures remove epileptogenic tissue. Disconnection procedures interrupt seizure pathways while limiting tissue removal. Laser ablation or radiofrequency techniques create targeted lesions. Neurostimulation may be considered when a seizure network cannot be safely removed.

Surgery is not only temporal lobectomy

Modern programmes assess temporal, frontal, parietal, occipital, insular, multilobar and hemispheric epilepsies. The operation or intervention is selected from the individual network anatomy rather than from one standard procedure.

Seizure freedom is not the only outcome

Presurgical counselling also considers cognition, mood, medication burden, injuries, independence, education, employment and quality of life. Some procedures are performed primarily to reduce seizure burden or dangerous falls rather than to achieve complete seizure freedom.

Histopathology matters

Resected tissue can reveal focal cortical dysplasia, hippocampal sclerosis, tumour, gliosis or another pathology that was subtle or invisible on MRI. Pathology can help explain the epilepsy and refine prognosis.

Multidisciplinary decision-making

Epileptologists, neurosurgeons, neuroradiologists, neuropsychologists, neurophysiologists, specialist nurses and other professionals review the evidence together. The final decision also depends on the person’s own priorities and acceptable level of risk.

Worldwide access

There is a major global treatment gap in epilepsy surgery. Barriers include delayed referral, limited video-EEG and imaging, shortages of specialist teams, cost and geographic concentration of surgical centres.

The central point

Presurgical assessment is a structured process for determining whether a seizure network can be treated effectively without unacceptable functional harm. Referral for assessment is not a commitment to undergo surgery.

SEEG →
FDG-PET →
Functional MRI →
Neuropsychology in Presurgical Epilepsy Assessment →
The Wada Test in Epilepsy Surgery →
MRI Post-Processing and Morphometric Analysis →

2025 systematic review and meta-analysis — MRI-negative epilepsy

Sources

NICE NG217 — Non-pharmacological treatments

ILAE Epilepsy Surgery Commission — reports and referral recommendations

Wiebe et al. — Randomised controlled trial of surgery for temporal-lobe epilepsy

This page provides general educational information and is not individual medical advice. Suitability for epilepsy surgery requires specialist multidisciplinary assessment.

Advanced presurgical science

Evidence checked: September 2026.