From the Guidelines
For a patient with new onset seizure, an MRI of the brain without IV contrast is usually appropriate in the assessment, as it provides a comprehensive evaluation of the brain and can help identify potential causes of the seizure. According to the American College of Radiology 1, MRI without contrast is a suitable choice for evaluating new-onset seizures unrelated to trauma. This recommendation is supported by a study published in the Journal of the American College of Radiology 1, which highlights the importance of MRI in identifying and characterizing focal causative lesions, as well as assessing progression and determining prognosis.
The use of non-contrast MRI is also preferred in stable patients, as stated in a policy statement published in Pediatrics 1, which recommends non-contrast MRI as the preferred imaging modality for children with seizures who require neuroimaging. The imaging protocol should include thin-section T1-weighted, T2-weighted, FLAIR, diffusion-weighted, and susceptibility-weighted sequences with coverage of the entire brain.
Key considerations for imaging in new-onset seizures include:
- Timing: Ideally, MRI should be performed within 24-72 hours of the seizure for optimal detection of acute changes.
- Patient stability: Non-contrast MRI is generally preferred in stable patients, while non-contrast CT may be acceptable if MRI is not readily available.
- Clinical context: Imaging may not be necessary for patients with a preexisting diagnosis of epilepsy if the seizure is typical of the patient's seizure semiology, but a low threshold for neuroimaging is prudent in patients who present with status epilepticus or who do not return to their neurologic baseline.
In certain situations, such as pregnancy, severe renal impairment, or known gadolinium allergy, a non-contrast MRI would be appropriate 1. However, the use of intravenous contrast may be useful when images without IV contrast are not sufficient or if neoplasm or inflammatory condition is suspected 1.
From the Research
Diagnostic Yield of MRI in New-Onset Seizures
- The diagnostic utility of contrast MR-imaging in adult new-onset seizures without clinically suspected neoplasia or infection is not well defined in the literature 2.
- A study found that 29/29 (100%) lesional abnormalities were detected on noncontrast sequences, suggesting that contrast MR-imaging has limited diagnostic utility in initial screening of adult new-onset seizure patients without clinically suspected neoplasia or infection 2.
- Another study found that brain MRI showed epileptogenic lesions in an additional 32% compared to brain CT, highlighting the importance of MRI in diagnosing new-onset epilepsy 3.
Role of MRI in Diagnosing New-Onset Seizures
- MRI is the current imaging tool of choice in the investigation of patients with seizures, and a dedicated seizure protocol can significantly increase the chances of identifying a cause 4.
- A study found that MRI detected potentially epileptogenic lesions in 59 patients (47%) with new-onset seizures, with the most common lesion type being infection and inflammation (28%) 4.
- Another study found that MRI reveals potentially epileptogenic lesions in a minority of patients with a newly diagnosed seizure disorder, with lesions being most common in patients who have experienced focal seizures 5.
Comparison of MRI with Other Diagnostic Tools
- A study found that the sensitivity of LT-EEG was higher than that of routine EEG (54.39% vs. 25.5%), and the sensitivity of MRI was higher than that of CT (67.98% vs. 54.72%) 3.
- Another study found that abnormal MRI and EEG were concordant in 18% of patients, with EEG being normal in 37% of patients with epileptogenic lesions 4.
- A review article discussed the indications for neuroimaging in patients with seizures and epilepsy, and highlighted the importance of MRI in identifying a causative focal lesion and helping to diagnose the epilepsy type 6.