MRI and Neuroimaging in Epilepsy

Diagnosis and specialist assessment

Brain imaging in epilepsy is not simply about finding a tumour or a large lesion. The goal is to identify structural abnormalities that may explain seizures, refine diagnosis and, in some people, guide surgical treatment.

Central point: A normal MRI does not rule out epilepsy, and a visible abnormality does not prove that it is causing the seizures. Imaging has to be interpreted alongside the clinical history, EEG and seizure pattern.

Who should have MRI?

NICE recommends MRI for children, young people and adults diagnosed with epilepsy unless they have idiopathic generalised epilepsy or self-limited epilepsy with centrotemporal spikes. The scan should follow a regionally agreed epilepsy MRI protocol and, after referral, should usually be completed within 6 weeks.

Why an epilepsy MRI protocol matters

Epilepsy imaging is more specialised than a generic brain MRI. Thin-slice, high-resolution sequences in appropriate planes improve the chance of identifying subtle abnormalities such as hippocampal sclerosis, focal cortical dysplasia, developmental malformations, small tumours, vascular lesions or consequences of previous injury.

NICE also recommends that scans are reported by a radiologist with appropriate neuroradiology expertise. If seizures continue despite treatment and the diagnosis remains unclear, specialist review of the original MRI within a tertiary epilepsy centre may reveal abnormalities that were not obvious on the first report.

What can MRI show?

Potential structural causes include hippocampal sclerosis, focal cortical dysplasia, brain tumours, vascular malformations, stroke, traumatic brain injury, congenital malformations and scarring after previous infection or inflammation. Some lesions are highly relevant to seizure generation; others may be incidental findings.

When CT is used

CT is faster and more widely available than MRI, so it has an important role in acute settings when bleeding, major trauma, stroke or another urgent structural problem is suspected. For detailed epilepsy investigation, however, MRI is usually more sensitive for subtle epileptogenic abnormalities.

NICE says CT can be considered when MRI is contraindicated. It also advises against routine CT for someone with established epilepsy who presents to an emergency department after a typical seizure unless there are additional concerns.

When is repeat MRI considered?

NICE recommends considering another MRI when the original study was suboptimal, when there are new features to the epilepsy, when a person with idiopathic generalised epilepsy or self-limited epilepsy with centrotemporal spikes has not responded as expected to first-line treatment, or when epilepsy surgery is being considered.

What if MRI is normal?

MRI-negative epilepsy is real. Some epileptogenic abnormalities are below the resolution of conventional imaging, some are difficult to recognise, and some epilepsies do not have a structural lesion visible on MRI. A normal scan should therefore never be used on its own to exclude epilepsy.

Imaging before epilepsy surgery

When surgery is being considered, imaging becomes part of a larger presurgical assessment rather than a standalone test. High-quality MRI is compared with seizure semiology, prolonged video-EEG and, where appropriate, neuropsychology and additional techniques such as PET, SPECT, functional MRI, MEG or intracranial EEG. The purpose is to determine whether the seizure-generating network can be treated without unacceptable harm to important functions.

Diagnosis and Tests · EEG Explained Properly · Causes of Epilepsy · Epilepsy Surgery and Presurgical Assessment

What a modern epilepsy MRI pathway should include

A normal routine MRI does not end the structural investigation when focal epilepsy remains strongly suspected. Modern assessment asks whether the scan used an epilepsy-specific acquisition protocol, whether it was reviewed by an experienced neuroradiologist with the electroclinical hypothesis available, and whether repeat imaging or post-processing could reveal a subtle lesion.

HARNESS-MRI and dedicated acquisition

The ILAE Neuroimaging Task Force developed the HARNESS-MRI approach to standardise high-resolution structural imaging in epilepsy. The central principle is harmonised, three-dimensional imaging with sequences designed to show cortical architecture, the grey–white junction and hippocampal structure clearly rather than relying on a generic brain MRI protocol.

Why 3T is often preferred

Three-tesla MRI provides higher signal-to-noise ratio than 1.5T and can improve depiction of subtle cortical and hippocampal abnormalities. Scanner field strength alone is not enough, however: sequence choice, slice orientation, motion control and expert interpretation can be just as important.

When repeat MRI is appropriate

Repeat MRI may be considered when earlier imaging was performed on an older scanner, used non-epilepsy protocols, was degraded by motion, preceded important changes in MRI technology, or conflicts with strong focal EEG and semiology. Children may also need repeat imaging because maturation and myelination can change lesion conspicuity.

MRI-negative does not mean lesion-free

A 2025 systematic review and meta-analysis found that the label “MRI-negative” is inconsistently applied across studies. Expert review and MRI post-processing can reveal previously unrecognised abnormalities, and the review found a substantial gain in diagnostic yield when post-processing was used systematically.

MRI post-processing

Morphometric and surface-based techniques can highlight abnormal cortical thickness, blurring of the grey–white junction and other subtle patterns associated with focal cortical dysplasia. These tools support, rather than replace, expert visual review.

Beyond conventional structural MRI

When high-quality structural MRI remains non-localising, selected people undergoing presurgical assessment may need FDG-PET, ictal SPECT, MEG, EEG source imaging, 7T MRI or intracranial EEG. The important principle is convergence: no single modality should be treated as a stand-alone proof of the epileptogenic zone.

Interpret imaging in the electroclinical context

Radiologists detect more clinically meaningful abnormalities when they know the suspected seizure onset, semiology and EEG findings. Conversely, an unexpected MRI lesion must not automatically be assumed to cause the epilepsy.

Worldwide access

High-quality epilepsy MRI depends not only on owning an MRI scanner but on access to appropriate protocols, trained radiographers, neuroradiology expertise and advanced post-processing. These resources remain unevenly distributed worldwide.

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

Sources

NICE NG217 — Diagnosis and assessment of epilepsy

NICE QS211 — Tertiary epilepsy services

This page provides general educational information and is not individual medical advice.

Evidence checked: September 2026.