Should an MRI with or without contrast (Magnetic Resonance Imaging) be used for a seizure workup?

MRI Without Contrast is the Preferred Imaging Modality for Seizure Workup

MRI of the brain without IV contrast is usually appropriate for the assessment of new-onset seizures unrelated to trauma, as it provides superior detection of epileptogenic lesions compared to other imaging modalities. 1

Initial Imaging Selection Algorithm

For New-Onset Seizures:

• Non-emergent setting: MRI brain without IV contrast is the imaging study of choice 1
• Emergent setting: CT head without IV contrast may be more appropriate due to quicker acquisition time and decreased requirements for safety screening 1, 2

For Patients with Known Seizures Requiring Surgical Planning:

• Either MRI head without IV contrast or MRI head without and with IV contrast are considered equivalent alternatives 1
• The decision to use contrast depends on the underlying suspected etiology of the seizures 1

Advantages of MRI Without Contrast for Seizure Evaluation

• MRI demonstrates excellent gray-white matter differentiation and multiplanar imaging capability 1
• Higher sensitivity for detecting epileptogenic lesions (70-80%) compared to CT (approximately 30%) 1, 2
• Superior visualization of hippocampal abnormalities, which are the most common cause of temporal lobe seizures 1, 3
• Better detection of cortical dysplasias and subtle structural lesions that may be missed on CT 2, 4
• Fluid-attenuated inversion recovery (FLAIR) imaging is particularly useful for evaluating the frontal lobes and hippocampus for mesial temporal sclerosis 3

When Contrast Should Be Considered

• When there is suspicion for neoplastic lesions (primary or metastatic tumors) 3, 5
• For evaluation of infectious or inflammatory lesions 3, 5
• In patients with new-onset seizures in adulthood or worsening of chronic seizures 3
• In patients with known seizure disorders requiring surgical planning, where contrast may help better define certain lesions 1

Limited Utility of Contrast in Most Seizure Evaluations

• In a study of pediatric patients with acute seizure presentation, only 5% of cases were retrospectively deemed to have necessitated the use of IV gadolinium 5
• Of 1010 patients with an initial non-contrast study, only 1.5% required repeat MRI with IV contrast to further evaluate findings 5
• For most common causes of epilepsy (hippocampal sclerosis, cortical dysplasia, gliosis), non-contrast MRI is sufficient 3, 6

Common Pitfalls to Avoid

• Assuming a normal CT excludes structural abnormality - MRI may still reveal significant pathology missed on CT 2, 7
• Using contrast routinely for all seizure evaluations - this is unnecessary in most cases and exposes patients to potential risks of gadolinium administration 8, 5
• Failing to use dedicated seizure protocols - acquisition on 3T magnets with specific sequences improves lesion detection 1
• Delaying appropriate imaging in patients with focal findings on neurologic examination, persistent headache, or recent history of head trauma, as these correlate with higher probability of finding structural abnormalities 1, 2

Special Considerations

• 20-30% of temporal epilepsy and 20-40% of patients with extra-temporal lobe epilepsy have no clear lesion seen on MRI despite having epileptogenic foci 1
• Patients are more likely to be seizure-free after surgery when focal circumscribed lesions are identified on presurgical MRI 1
• In patients with MRI-negative epilepsy, functional imaging techniques like PET or SPECT may provide complementary information 6, 4