MRI for Epilepsy: Brain Imaging Guide

Epilepsy is the most common serious neurological condition, affecting around 600,000 people in the UK — roughly 1 in 100. It causes recurrent seizures due to abnormal electrical activity in the brain. MRI is essential in epilepsy because it identifies structural brain abnormalities that cause seizures in approximately 25-30% of patients. Finding a structural cause changes management significantly — particularly for patients whose seizures are not controlled by medication and who may be candidates for epilepsy surgery.

If you have had a first seizure, have been diagnosed with epilepsy, or have seizures that are not responding to medication, a brain MRI with an epilepsy-specific protocol is one of the most important investigations you can have.

Why MRI Matters in Epilepsy

MRI in epilepsy serves several purposes:

• Identifying the cause — structural lesions (tumours, cortical malformations, scarring, vascular malformations) cause seizures in 25-30% of patients. Removing or treating the lesion can cure the epilepsy.
• Guiding surgical planning — for patients with drug-resistant epilepsy (about 30% of all epilepsy patients), MRI identifies the seizure focus and its relationship to critical brain areas. Epilepsy surgery can achieve seizure freedom in 60-80% of carefully selected patients.
• Excluding serious pathology — a first seizure in an adult always warrants MRI to rule out brain tumours, vascular malformations, and other structural causes.
• Prognostic information — certain MRI findings (e.g. hippocampal sclerosis) have well-established treatment pathways and surgical outcomes.

Structural Causes of Epilepsy Visible on MRI

• Hippocampal sclerosis (mesial temporal sclerosis) — the most common MRI finding in temporal lobe epilepsy. The hippocampus (memory structure in the temporal lobe) appears small, bright on T2/FLAIR, and has lost its internal structure. Found in about 60-70% of patients with temporal lobe epilepsy. Anterior temporal lobectomy (surgery to remove the affected hippocampus and surrounding temporal lobe) achieves seizure freedom in 60-80% of these patients.
• Focal cortical dysplasia (FCD) — an area where the brain cortex did not develop normally. The second most common cause of drug-resistant epilepsy. MRI shows cortical thickening, blurring of the grey-white matter junction, and sometimes a bright tail extending towards the ventricle (the "transmantle sign"). Some FCDs are very subtle and require expert neuroradiological review and high-resolution MRI.
• Brain tumours — low-grade tumours (gangliogliomas, DNETs — dysembryoplastic neuroepithelial tumours) are common causes of chronic epilepsy in young people. They grow very slowly and are often curable by surgery.
• Cavernomas (cavernous malformations) — clusters of abnormal blood vessels. Appear as a "popcorn-like" lesion with a dark haemosiderin rim on T2*-weighted images. Common — found in about 0.5% of the population, but only a proportion cause seizures. Surgical removal can cure the epilepsy.
• Arteriovenous malformations (AVMs) — tangles of abnormal blood vessels. Can cause seizures, haemorrhage, or both.
• Post-traumatic or post-surgical scarring (gliosis) — bright areas on FLAIR in locations corresponding to previous brain injury.
• Encephalocele, polymicrogyria, heterotopia — other developmental brain abnormalities (malformations of cortical development) that can be epileptogenic.

Epilepsy-Specific MRI Protocol

A standard brain MRI may miss subtle epilepsy-related abnormalities. An epilepsy protocol includes:

• High-resolution 3D T1-weighted sequence — thin slices (typically 1mm) covering the entire brain. Allows detailed assessment of cortical structure and reformatting in any plane.
• High-resolution FLAIR — the most sensitive sequence for subtle cortical and white matter abnormalities.
• Coronal T2-weighted and FLAIR images angled perpendicular to the hippocampus — specifically designed to assess the hippocampi for sclerosis. Hippocampal volume and signal are compared side to side.
• T2*-weighted (gradient echo) or SWI (susceptibility-weighted imaging) — detects blood products and calcification. Essential for cavernomas.
• 3T field strength — higher field strength MRI (3 Tesla vs standard 1.5 Tesla) provides better resolution and is recommended for epilepsy imaging where available.

An epilepsy-protocol MRI takes 30-45 minutes.

What MRI Cannot Show

• Electrical activity — MRI shows brain structure, not function. EEG (electroencephalogram) is needed to record seizure activity and localise the electrical focus.
• All epileptogenic lesions — approximately 30-50% of epilepsy patients have a normal MRI (MRI-negative epilepsy). This does not mean there is no structural abnormality — the lesion may be too small or too subtle for current MRI technology. Advanced techniques (7T MRI, post-processing software, PET-MRI co-registration) can detect some of these.
• Seizure type or frequency prediction — MRI findings do not predict seizure frequency or severity.

Alternative and Complementary Tests

• EEG — records brain electrical activity. Standard EEG, ambulatory EEG (24-48 hours at home), or video-EEG telemetry (continuous recording in hospital with video) to capture seizures and localise the focus.
• FDG-PET — shows areas of reduced brain metabolism between seizures, which often correspond to the seizure focus. Useful when MRI is normal.
• SPECT (ictal and interictal) — shows blood flow patterns during and between seizures. Increased blood flow during a seizure localises the focus.
• MEG (magnetoencephalography) — records magnetic fields from brain activity. Can localise epileptic sources with high spatial accuracy.
• Neuropsychological testing — assesses memory, language, and cognitive function. Helps predict surgical risk (particularly memory outcome after temporal lobe surgery).
• Intracranial EEG — electrodes placed directly on or in the brain during a separate operation. Used when non-invasive tests have not clearly identified the seizure focus. The final step before epilepsy surgery in complex cases.

Treatment Pathways

• Anti-seizure medications (ASMs) — first-line treatment. Around 70% of patients achieve seizure control with medication. Common ASMs include levetiracetam, lamotrigine, sodium valproate (not in women of childbearing age), carbamazepine, and lacosamide. Choice depends on seizure type, age, sex, and other medications.
• Drug-resistant epilepsy — defined as failure of two appropriate ASMs. Affects approximately 30% of patients. These patients should be referred to an epilepsy surgery centre for assessment.
• Epilepsy surgery — the most effective treatment for drug-resistant focal epilepsy. Options include:
  • Anterior temporal lobectomy — for hippocampal sclerosis. Seizure freedom in 60-80%.
  • Lesionectomy — removal of a discrete lesion (tumour, FCD, cavernoma). Seizure freedom in 60-90% depending on lesion type and completeness of removal.
  • Laser interstitial thermal therapy (LITT) — MRI-guided, minimally invasive ablation. Increasingly used for hippocampal sclerosis and small deep lesions.
• Vagus nerve stimulation (VNS) — an implanted device that delivers electrical stimulation to the vagus nerve. Reduces seizure frequency by 30-50% in many patients. Does not usually achieve complete seizure freedom.
• Ketogenic diet — high-fat, low-carbohydrate diet. Primarily used in children with drug-resistant epilepsy. Can be effective in some adult patients.

UK Statistics

• Epilepsy affects around 600,000 people in the UK (1 in 100)
• Around 87 people are diagnosed with epilepsy every day in the UK
• 70% achieve seizure control with medication; 30% are drug-resistant
• Only 3-4% of people with drug-resistant epilepsy are referred for surgical assessment, though many more could benefit
• Epilepsy surgery achieves seizure freedom in 60-80% of well-selected candidates
• Epilepsy-related deaths (SUDEP — Sudden Unexpected Death in Epilepsy) account for approximately 1,000 deaths per year in the UK

Frequently Asked Questions

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