Neurosurgery notes/Functional/Seizure/Work-up of seizures

Work-up of seizures

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Status
Done
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Parent item
Seizure
Sub-item
Work up paeds
Electroencephalogram (EEG)
Radiology assessment for epilepsy
Neuropsychological assessment for epilepsy

Definition

  • Epileptogenic zone (EZ):
    • A theoretical region of cortex that if removed would result in seizure freedom;
    • The cortical area indispensable for the generation of epileptic seizures
  • Ictal onset zone (IOZ)
    • Aka: Seizure onset zone
    • The cortical area actually generating seizures
    • EZ is larger than the IOZ
    • Removing the IOZ does not 100% causes lasting seizure freedom
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Aim

  • Find concordance between history, exam, neuropsychology, neuropsychiatry, EEG and imaging
    • If there is concordance for indicating a single dysfunctional area that may be removed without causing a deficit + if there is no evidence that the rest of the brain is abnormal, no further investigations are required → proceed to surgery
    • If, however, MRI is normal or shows dual or extensive pathology or if the scalp EEG and structural data are discordant, then further investigation with Phase 2 study ([18F]FDG PET, ictal SPECT, and MEG)
      • The results of these tests are not likely to lead directly to a surgical solution, but may guide the placement of intracranial EEG electrodes with a combination of depth and subdural electrodes.

Evaluation

  • Preop assessment
    • All will go through phase 1 but only some will require phase 2
    • Phase 1
      • History / Examination
      • MRI (3T)
      • Interictal EEG
      • Video telemetry EEG
      • Neuropsychology
      • Neuropsychiatry
      • (Neuro-ophthalmology)
    • Phase 2
      • PET
      • SPECT
      • MEG
      • EEG-fMRl
      • ESI
      • fMRl
      • DTI
      • ECoG
      • SSEPs/ Motor Stim
      • SEEG / Subdural grid
  • If the individual has an unremarkable optimal MRI scan or if an abnormality on MRI is discordant with clinical and EEG data, further imaging is done to try to infer the location of the epileptogenic cortex:
    • Fluorodeoxyglucose ([18F]FDG) PET
    • Ictal SPECT
    • Magnetoencephalography (MEG)
      • To infer the location of interictal epileptic discharges.
  • Invasive monitoring
    • Is unnecessary when there is → proceed to surgery
      • Concordance between interictal and ictal video-EEG scalp recordings localizing to the nondominant temporal lobe AND
      • Ipsilateral mesial temporal sclerosis on MRI AND
      • Contralateral language and memory dominance on Wada testing (with congruent neuropsychological testing), AND
      • Ipsilateral PET hypometabolism of the temporal lobe, AND
      • Perhaps magnetoencephalographic data.
    • 50-90% of such patients will be rendered free of seizures postoperatively.
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