The EEG evaluation of single photon emission computed tomography abnormalities in epilepsy

Single photon emission computed tomography (SPECT) has increasingly been us ed as a diagnostic procedure for localizing epileptic seizure foci and as a research tool for investigating the physiologic mechanisms underlying seiz ure activity. With increasing use of SPECT in localizing the seizure focus for epilepsy surgery, there arises a need to critically assess its current role in the evaluation of patients for epilepsy surgery, especially as it r elates to other clinical and laboratory data used in presurgical evaluation . Ictal EEG discharge has traditionally been used as the "gold standard" ag ainst which SPECT studies are compared in assessing the latter's localizing value. However, this practice presents a major challenge because SPECT stu dies are often reserved for patients with nonlocalizing EEG or magnetic res onance imaging findings. Nonetheless, SPECT studies in evaluation for epile psy surgery should always be performed with the knowledge of the patient's EEG activity preceding, during, and after the injection of the radiotracer. The advent of techniques such as subtraction SPECT with co-registration on magnetic resonance imaging (SISCOM) and computer image-guided surgery has great potential in enhancing the clinical electrophysiologic evaluation of SPECT-detected abnormalities in epilepsy. These techniques permit accurate spatial correlation between intracranial EEG activity and SPECT perfusion p atterns. The techniques can also be used to evaluate the effect of the exte nt of EEG focus resection compared with that of SISCOM focus resection to d etermine which has more prognostic importance in postsurgical control of se izures. Both animal and human studies are warranted to advance our knowledg e of the electrophysiology associated with the various SPECT perfusion patt erns.