What are the recommendations for neuroimaging in a patient presenting with a first seizure episode?

Neuroimaging Recommendations for First Seizure Episode

In patients presenting with a first seizure episode, MRI is the imaging study of choice in non-emergent situations, while CT should be performed emergently when immediate access to the patient is needed or when acute intracranial pathology requires rapid assessment. 1

Emergent Neuroimaging (CT)

Noncontrast CT should be performed emergently in patients with:

• Need for immediate access to the patient during scanning 1
• Suspicion of acute intracranial pathology requiring urgent intervention 1
• Persistent altered mental status 1
• New focal neurologic deficits 1
• Recent head trauma 1
• Persistent headache 1
• History of malignancy 1
• Immunocompromised state 1
• Fever 1
• History of anticoagulation 1
• Age older than 40 years 1
• Focal onset before generalization 1

CT is particularly valuable for rapidly identifying:

• Intracranial hemorrhage
• Stroke
• Vascular malformations
• Hydrocephalus
• Space-occupying lesions
• Calcified lesions 1

Non-emergent Neuroimaging (MRI)

MRI is superior to CT for:

• Identifying and characterizing focal causative lesions 1
• Assessing progression of lesions 1
• Determining prognosis 1
• Guiding treatment strategy 1
• Detecting lesions in orbitofrontal and medial temporal regions 1
• Detecting small cortical lesions 1

MRI protocols should include:

• Coronal T1-weighted (3 mm) imaging perpendicular to the long axis of the hippocampus
• High-resolution volume (3-D) acquisition (T1-weighted, gradient echo) with 1-mm isotropic voxels
• Coronal T2 and coronal/axial fluid-attenuated inversion recovery sequences 1

Special Considerations

Adults

• Neuroimaging is recommended for all adults with first seizure 2, 3
• When feasible, perform neuroimaging in the ED on patients with a first-time seizure 1
• Deferred outpatient neuroimaging may be used when reliable follow-up is available 1

Children

• MRI is rarely indicated in neurologically normal children with generalized seizures 1
• Only 2% of low-risk pediatric patients (without predisposing conditions or focal seizures) have abnormal imaging findings 1
• Neuroimaging is recommended for children with:
  • Focal neurologic deficits 3
  • History of head trauma 3
  • History of malignancy 3
  • Abnormal neurological examination 1

Limitations and Pitfalls

1. CT limitations:

   • Lower sensitivity compared to MRI (only 30% success in detecting lesions in focal epilepsies) 1
   • Poor visualization of orbitofrontal and medial temporal regions 1
   • Limited detection of small cortical lesions 1

2. Follow-up considerations:

   • Concerns about timely follow-up and social issues may influence the decision for immediate versus deferred imaging 1
   • Patients with normal neurologic examination, no comorbidities, and no known structural brain disease who have returned to baseline may have imaging deferred if reliable follow-up is assured 1

3. Yield considerations:

   • Some forms of epilepsy have low yield of structural lesions on MRI (typical forms of primary generalized epilepsy, benign focal epilepsies of childhood with characteristic EEG features) 1

Advanced Imaging Techniques

For complex or refractory cases, consider:

• FDG-PET/CT for localization of epileptogenic foci (not indicated for initial evaluation) 1
• Specialized MRI protocols with 3T scanners for intractable seizures 1

Remember that neuroimaging is just one component of the comprehensive evaluation of a first seizure, which should also include appropriate laboratory testing and electroencephalography within 24-48 hours of the event 2.