Science & Discovery
A normal-looking MRI can coexist with focal epilepsy. Sometimes the problem is not that there is no lesion — it is that the lesion is too subtle for the scan, protocol or human eye to show clearly.
The key idea: “MRI-negative” describes what has been seen on imaging, not proof that the brain contains no structural epileptogenic abnormality.
Focal cortical dysplasia is one of the clearest examples. It is a malformation of cortical development that can generate seizures, yet some dysplasias are extremely small, sit deep at the bottom of a sulcus or produce only subtle changes in cortical thickness and signal.
Why the first scan can miss something
Detection depends on several things: scanner strength, slice thickness, the sequences used, whether an epilepsy-specific protocol was performed, image quality, the age of the person being scanned and the experience of the reader. A generic brain MRI is not the same thing as a dedicated epilepsy MRI reviewed by an expert neuroradiologist.
What newer methods add
High-field MRI, targeted re-review, quantitative post-processing and machine-learning approaches can sometimes identify abnormalities that were not apparent on the original scan. A 2026 systematic review of MRI techniques for focal cortical dysplasia found that advanced imaging and computational methods can improve detection in subtle or previously MRI-negative cases.
A broader systematic review and meta-analysis of MRI-negative epilepsy also found that post-processing increased diagnostic yield, reinforcing the idea that “negative” depends partly on how the images are acquired and analysed.
Pathology can reveal what imaging did not
Studies of people with drug-resistant focal epilepsy have found structural pathology — including focal cortical dysplasia, gliosis and hippocampal sclerosis — in tissue from some people whose preoperative MRI had been reported as negative. That does not mean every MRI-negative epilepsy has a hidden lesion, but it demonstrates why a negative scan cannot be treated as the end of the investigation.
Why this matters for surgery
People with MRI-negative focal epilepsy can still be considered for specialist presurgical evaluation. The challenge is localisation: teams may need to combine seizure semiology, video-EEG, PET, SPECT, MEG, neuropsychology, advanced MRI analysis and, in selected cases, stereo-EEG before deciding whether treatment can safely target a seizure-generating region.
Sources
MRI-negative epilepsy — systematic review and meta-analysis
Snell et al. (2026) — MRI techniques for detecting focal cortical dysplasia