Surgical Treatments for Epilepsy

What is epilepsy, and how are seizures classified?

Not all epilepsies are the same—and accurate classification is the foundation of accurate treatment.

Based on international criteria, we diagnose epilepsy when:

• at least two unprovoked seizures have occurred, or
• a single seizure has occurred, but the brain carries a lasting change that substantially increases the risk of recurrence (e.g., gliosis, tumor, cortical dysplasia).

Seizures are commonly classified as:

• Focal: begin in one hemisphere. Awareness may be preserved or impaired. Symptoms can be motor, sensory, cognitive/psychological, or autonomic.
• Generalized: rapidly engage both hemispheres. These include tonic-clonic, myoclonic, atonic, absence seizures, and others.
• Unknown onset: e.g., epileptic spasms, when early features do not clearly define the onset pattern.

Distinguishing focal from generalized epilepsy is crucial: it determines whether a realistic surgical pathway exists, and which options are appropriate.

What happens in the brain during a seizure?

An “electrical storm”—when excitation outweighs inhibition.

At the core of a seizure, a group of neurons enters a state of hyperexcitability and fires synchronously, repeatedly. At the same time, normal inhibitory circuits that typically contain this activity become less effective.

A seizure may:

• remain localized (focal), or
• spread through networks across a hemisphere or both hemispheres (secondary generalization).

The underlying “imbalance” of excitation versus inhibition can reflect structural lesions, genetic/metabolic factors, or cryptogenic causes. Understanding the responsible network and seizure circuit is what helps us choose between resection, disconnection, or neuromodulation.

When is epilepsy considered drug-resistant?

The pivotal moment when medications are no longer enough—and surgery should be discussed proactively.

The international definition of drug-resistant epilepsy is: failure of two appropriately chosen, well-tolerated antiseizure medication regimens (alone or in combination) to achieve sustained seizure freedom.

After that threshold:

• the likelihood of seizure control with yet another medication becomes low
• side effects from further escalation often increase
• valuable time may be lost that could be used for a structured evaluation of surgical and device-based options.

Who is a candidate for surgical treatment?

The right patient, the right timing, and the right operation.

A patient is typically considered a surgical candidate when:

• they have clearly drug-resistant epilepsy
• seizures originate from a relatively defined region (a focus) rather than being primarily generalized
• that region can be resected, disconnected, or modulated without unacceptable permanent neurological deficit.

Profiles that are often favorable for potentially curative surgery include:

• mesial temporal lobe epilepsy with hippocampal sclerosis
• focal epilepsy with a clear MRI lesion (tumor, dysplasia, gliosis)
• pediatric/young patients with unilateral, destructive pathology and pre-existing major deficits.

In multifocal or primarily generalized epilepsy, the goal is often palliative: reducing seizure frequency and severity, and lowering the risk of injury.

How does the presurgical evaluation work (Phase 1 & Phase 2)?

From clinical history and video–EEG to intracranial electrodes when indicated.

Presurgical evaluation is commonly divided into noninvasive (Phase 1) and invasive (Phase 2) monitoring.

Phase 1 — Noninvasive evaluation

• Detailed history & seizure semiology analysis
• Prolonged video–EEG monitoring, often with carefully supervised medication reduction
• High-resolution epilepsy-protocol MRI to identify MTS, dysplasia, gliosis, vascular lesions, or neoplastic causes
• Neuropsychological assessment (memory, language, executive function)
• When needed: PET, SPECT, fMRI, MEG for additional localization in complex cases

Phase 2 — Intracranial electrodes

When findings are unclear or discordant, intracranial recording may be recommended, using subdural grids/strips or depth electrodes (stereo-EEG). Goals include:

• precise 3D localization of seizure onset and propagation pathways
• functional mapping of language, motor, sensory, and visual cortex
• defining safe resection or disconnection boundaries.

What are the main resective procedures?

When we can remove the seizure focus with an acceptable functional trade-off.

These procedures aim for complete removal of the epileptogenic zone (a potentially curative operation) or the lesion driving seizures:

• Resection of an epileptogenic focus: removal of a tumor, dysplasia, gliotic scar, or vascular lesion that matches the seizure onset region.
• Anterior temporal lobectomy (ATL): a classic operation for mesial temporal sclerosis, with high rates of durable seizure remission in appropriately selected patients.
• Selective amygdalohippocampectomy (SAH): selective removal of mesial temporal structures while preserving more of the lateral temporal neocortex.
• Tailored frontal, parietal, or occipital resections: individualized based on focus location and proximity to eloquent cortex.
• Multilobar resections: when the epileptogenic zone spans more than one lobe.

For every resection, the decision is always two-fold: how much seizure control we can realistically achieve, and which functions may be at risk (language, memory, vision, movement).

What about extratemporal epilepsy?

Complex epilepsies often require advanced mapping.

Surgery for extratemporal epilepsy (frontal, parietal, or occipital) is often more demanding because:

• seizures can spread very rapidly
• onset may be deep and difficult to capture on standard scalp EEG
• MRI may appear normal (nonlesional epilepsy).

In these cases, evaluation often requires:

• Phase II intracranial monitoring for precise localization
• intraoperative and/or awake mapping of language and motor function
• careful planning so the resection provides meaningful benefit while minimizing unacceptable permanent deficits.

What is hemispherectomy?

A definitive option for severe, unilateral, destructive epilepsies—most commonly in children.

In some children and young patients, one hemisphere may be extensively diseased (e.g., Rasmussen encephalitis, large cortical malformations, remote infarcts) and can drive frequent, disabling seizures.

In these patients, the most effective surgical strategies include:

• Anatomic hemispherectomy: near-complete removal of the affected hemisphere (used less commonly today due to complication profiles).
• Functional hemispherectomy: a combination of limited resection and extensive disconnection, aimed at stopping seizure spread without removing the entire hemisphere.

These operations are performed in patients who already have significant pre-existing deficits (e.g., hemiparesis), but they can provide a dramatic reduction in seizures, support cognitive development, reduce hospitalizations, and improve overall quality of life.

Which palliative procedures exist (callosotomy, MST)?

When we cannot remove the focus, we may be able to “disconnect” the networks.

When seizures are multifocal or generalized, or when the focus lies within eloquent cortex, the goal is to reduce the risk of falls, injuries, and prolonged seizures.

Corpus callosotomy

Partial or complete sectioning of the corpus callosum to limit bilateral seizure spread—especially helpful for drop attacks (tonic-clonic or atonic seizures).

Multiple Subpial Transections (MST)

When a seizure focus overlaps language or motor cortex and cannot be removed safely, MST uses multiple vertical cortical incisions to disrupt the horizontal connections that synchronize seizure activity, while preserving—as much as possible—the vertical functional “columns” of cortex.

These procedures rarely eliminate seizures entirely, but they can meaningfully reduce severity and frequency, and lower injury risk.

What are VNS, DBS & RNS — modern neuromodulation?

Implantable, adjustable, and reversible options for multifocal or nonresectable epilepsy.

Vagus nerve stimulation (VNS)

A pulse generator is implanted subcutaneously below the clavicle, with a lead placed on the left vagus nerve. The device delivers programmed stimulation that can reduce seizure frequency and severity. Long term, about half of patients achieve ≥50% seizure reduction.

Deep brain stimulation (DBS)

Electrodes are placed in deep brain targets (e.g., the anterior nucleus of the thalamus) and connected to an implantable pulse generator. DBS is used primarily for refractory focal epilepsies, with improvement that often increases over time.

Responsive neurostimulation (RNS)

A system that detects epileptiform activity locally (via cortical or depth leads) and responds in real time with targeted stimulation to interrupt the event before it becomes a clinical seizure. It is particularly helpful when there are 1–2 foci that are not safe to remove surgically.

A shared advantage of neuromodulation strategies is reversibility, programmability, and tissue preservation.

Risks, complications & balancing benefit vs risk

The most important question is not “is there risk?”—but “what risk do I face if I do nothing?”

Any brain procedure carries risks: bleeding, infection, CSF leak, transient or permanent neurological deficits, and device-related complications. But drug-resistant epilepsy also carries substantial risk, including:

• serious falls, fractures, and injuries
• loss of independence, work limitations, and driving restrictions
• psychological burden on patients and families
• risk of sudden unexpected death in epilepsy (SUDEP)

In practice, we weigh:

• how likely seizures are to improve or stop
• the functional “cost” of the procedure
• available alternatives—or the absence of realistic alternatives
• what an “acceptable outcome” means for you personally.