MRI Brain Imaging for Seizures: With or Without Contrast
For new-onset seizures in a non-emergent setting, order MRI brain WITHOUT contrast—this is the imaging study of choice and contrast adds no diagnostic value in the absence of suspected neoplasia or infection. 1, 2
Clinical Context Determines Imaging Strategy
New-Onset Seizures (Non-Emergent)
- MRI brain without IV contrast is the preferred imaging modality, with 70-80% sensitivity for detecting epileptogenic lesions compared to only 30% for CT 2, 3
- The superior gray-white matter differentiation and multiplanar capability of MRI makes it ideal for identifying hippocampal abnormalities (the most common cause of temporal lobe seizures), cortical dysplasias, and subtle structural lesions 2, 4
- Contrast is NOT routinely necessary—a 2021 study of 103 consecutive seizure patients found 100% of epileptogenic lesions were detected on non-contrast sequences alone, with zero lesions detected exclusively on post-contrast imaging 5
New-Onset Seizures (Emergent Setting)
- CT head without contrast is more appropriate initially when rapid assessment is needed, the patient requires close monitoring, or immediate neurosurgical intervention may be necessary 1, 3
- CT can quickly identify life-threatening pathology like intracranial hemorrhage, stroke, or mass effect requiring urgent intervention 3
- Follow up with outpatient MRI brain without contrast within 1-2 weeks, as CT misses 19% of structural abnormalities that MRI subsequently detects 3, 6
When to Add Contrast
Add IV contrast to your MRI order only in these specific scenarios: 4
- Suspected neoplasm (new-onset seizures in adults, progressive neurological deficits, or known history of cancer) 7
- Suspected infection (fever, immunocompromised state, or clinical signs of CNS infection) 7
- Suspected inflammatory condition (autoimmune encephalitis, demyelinating disease) 4
- Initial non-contrast images are insufficient or equivocal 4
The evidence strongly supports this selective approach: using contrast routinely in new-onset seizures without these red flags results in 72% unnecessary contrast administrations, costing an estimated $103,680 per 1000 patients while exposing patients to gadolinium without diagnostic benefit 5.
Optimal MRI Protocol Components
Request a dedicated seizure protocol that includes: 4
- Coronal T1-weighted imaging (3mm slices) perpendicular to the hippocampal long axis
- High-resolution 3D T1-weighted gradient echo with 1mm isotropic voxels
- Coronal T2-weighted sequences
- Coronal and axial FLAIR sequences
- 3T MRI is preferred over 1.5T when available for improved lesion detection 4
Surgical Planning Context
For patients with known seizure disorder requiring surgical evaluation, both MRI without contrast and MRI without/with contrast are considered equivalent alternatives 1
- Order only ONE of these options—they provide equivalent clinical information for surgical planning 1
- FDG-PET/CT may be added as a complementary functional tool, particularly when MRI is normal but seizures persist (sensitivity 87-90% for temporal lobe epilepsy) 4
Common Pitfalls to Avoid
- Don't assume normal CT excludes structural pathology—MRI reveals significant epileptogenic lesions in 22% of patients with normal neurologic exams and may detect abnormalities in 29% of cases where CT was normal 3, 6
- Don't order contrast reflexively—the 2021 study demonstrated 100% sensitivity of non-contrast sequences alone for epileptogenic lesions in appropriate patient populations 5
- Don't skip MRI in patients who had emergency CT—arrange outpatient MRI follow-up as CT's 30% sensitivity means most epileptogenic lesions will be missed 2, 3