MRI for Brain in Seizures
In general, all patients with epilepsy should undergo brain MRI as it is the imaging study of choice in nonemergent situations, with specific high-priority indications including focal neurologic findings, abnormal EEG, persistent headache, recent head trauma, or multiple/prolonged seizures. 1
When MRI is Indicated
High-Priority Situations (Obtain MRI Promptly)
- Focal findings on neurologic examination - these patients have high probability of structural abnormalities 1
- Abnormalities on EEG - strongly correlated with finding structural lesions 1
- Persistent headache 1
- Recent history of head trauma 1
- Multiple seizures at presentation 2
- Prolonged seizures lasting ≥5 minutes 2
- Developmental delay 2
A recent 2025 pediatric study found that patients with one or more of these risk factors (multiple seizures, prolonged duration, or developmental delay) had 94% sensitivity for detecting epileptogenic lesions, while those without any risk factors had only 6.3% yield and zero emergent findings 2.
General Epilepsy Population
MRI should be obtained in all patients with epilepsy for identifying causative lesions, determining prognosis, and guiding treatment strategy 1.
Exceptions Where MRI May Be Deferred
Some epilepsy forms have low yield for structural lesions and imaging may not be necessary 1:
- Primary generalized epilepsy with typical clinical features
- Benign focal epilepsies of childhood with characteristic clinical and EEG features
- Early onset childhood epilepsy with occipital spikes that responds adequately to antiepileptic drugs
Acute/Emergent Situations: Use CT First
In the emergent setting, noncontrast CT should be performed first as it rapidly identifies life-threatening pathology requiring urgent intervention 1:
- Intracranial hemorrhage
- Stroke
- Mass effect with herniation or midline shift
- Hydrocephalus
- Tumors
Important caveat: CT detects focal lesions in epilepsy with only 30% success rate compared to MRI 1. Therefore, even if CT is performed emergently, MRI should still be obtained subsequently in the nonemergent setting.
Optimal MRI Protocol
The protocol should be specifically designed for epilepsy evaluation, not just a routine brain MRI 1:
Essential Sequences
For hippocampal evaluation (hippocampal sclerosis is the most common cause of temporal lobe seizures):
- Coronal T1-weighted imaging (3 mm slices) perpendicular to the long axis of the hippocampus
- Coronal T2-weighted sequences
- Coronal and axial FLAIR sequences to assess for hippocampal signal abnormality, atrophy, and loss of internal structure 1
For cortical malformations (focal cortical dysplasia, polymicrogyria):
- High-resolution 3D T1-weighted gradient echo (GRE) with 1-mm isotropic voxels
- 3D FLAIR sequences 1
These high-resolution 3D sequences are critical for detecting malformations of cortical development, including focal cortical dysplasia and focal polymicrogyria that may be amenable to surgery 1.
Contrast Administration
IV contrast is NOT routinely necessary 1.
Use contrast only when:
- Images without contrast are insufficient
- Neoplasm is suspected
- Inflammatory condition is suspected 1
Common Pitfalls to Avoid
Don't rely on CT alone - it misses 70% of focal epilepsy lesions that MRI would detect 1
Don't use routine brain MRI protocols - epilepsy-specific protocols with dedicated hippocampal sequences and high-resolution 3D imaging are essential for detecting subtle epileptogenic lesions 1, 3
Don't skip MRI in "low-risk" patients without careful consideration - while certain primary generalized epilepsies may not require imaging, this determination requires characteristic clinical and EEG features 1
In trauma-related seizures, MRI has secondary role acutely due to longer scan time and safety screening requirements, but should be obtained after initial CT if focal neurologic findings persist 1