Case Study

A 28 year-old right-handed white female was admitted to the EMU for a pre-surgical evaluation of drug-resistant focal seizures. Seizure onset occurred at 15 years without risk factors and a single seizure semiology. Seizures began with an indescribable feeling of fear and nausea prior to a stare, lip smacking, motion arrest, and left post-ictal nose rubbing. A high-resolution brain MRI was normal. PET had equivocal reduction in regional cerebral metabolism in the left temporal lobe. EEG demonstrated left>right bitemporal sharp waves (90:10). 3 focal seizures were captured possessing the semiology as described revealing left hemispheric rhythmic ictal theta onset. Wada demonstrated left hemisphere dominance for language and bilateral memory function. A subtraction ictal SPECT co-registered with MRI (SISCOM) functional imaging was obtained below.

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Figure: Anatomic T1 coronal imaging with (A) a 3-T high resolution brain MRI with epilepsy protocol and B Diffusion Tensor Imaging with symmetric white matter tracts in the temporal lobes with high FA (arrow) delineating the integrity of medial amygdalohippocampal gray in a patient with a VFD .

How did SISCOM play a role?

SISCOM is a recently developed neuroimaging technique evaluating regional cerebral blood flow (rCBF) in both pediatric and adult patients with drug-resistant focal epilepsy during pre-surgical evaluation. Injection of a radiotracer (usually Tc-99m) during the ictus allows measure of local differences in rCBF between the ictal and interictal state of neuronal activation that occurs with seizures. Focal cerebral hyperperfusion noted on SISCOM (above) has been valuable for the identifying the seizure onset zone in 40-86% of patients in addition to assessing the extent of resection in temporal and extratemporal lobe epilepsy (1, 2). SISCOM findings may alter the decision to place or avoid pursuing invasive video-EEG (vEEG) in cases of successful outcomes (1) and complete resection of the area of involvement has been associated with a greater likelihood of becoming seizure-free after surgery. Rarely, discordant findings between invasive vEEG and SISCOM are reported in patients not seizure-free after surgery likely reflecting identification of a propagated rCBF pattern as opposed to the seizure onset zone (2). SISCOM will help restrict the iEEG electrode array and is anticipated to limit the extent of initial surgical resection for epilepsy in our patient.

References

  1. So EL. Integration of EEG, MRI, and SPECT in localizing the seizure focus for epilepsy surgery. Epilepsia 2000;41(suppl 3):S48-S54.
  2. Ahnlide J-A, Rosen I, Tech PL-M, Kallen K Does SISCOM contribute to favorable seizure outcome after epilepsy surgery? Epilepsia 2007;48(3):579-588.
Authored By: 
William O. Tatum DO
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Authored Date: 
07/2011