SPECT and PET in nonlesional epilepsy

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Abstract
Background: Positron emission tomography (PET) and single-photon emission computed tomography (SPECT) are applied in epilepsy mostly during presurgical assessment. Nonlesional focal epilepsy is very challenging for presurgical evaluation in cases of refractory epilepsy.Objectives: We aimed to investigate the contribution of PET and SPECT to focus localization in nonlesional epilepsy.Methods: The basic principles of SPECT and PET including different tracers were reviewed. The literature and the most recent publications are discussed in view of findings in nonlesional epilepsy.Results: Ictal SPECT shows a high sensitivity of over 80% for ictal onset zone in nonlesional epilepsy. Postprocessing with subtraction ictal SPECT co-registered with MRI (SISCOM) or statistical parametric mapping are the gold standard. Histopathological findings in nonlesional epilepsies with concordant ictal SPECT imaging show focal cortical dysplasia in up to 75% of cases. Ictal injection is unsuccessful in approximately 20% of cases and the procedure is very time consuming and labor intensive. Fluorodeoxyglucose (FDG)-PET in nonlesional epilepsy shows variable sensitivity of 46–76%. As with ictal SPECT, it benefits from postprocessing of co-registration with magnetic resonance imaging (MRI) or even statistical parametric mapping. Hybrid PET/magnetic resonance imaging (MRI) scanners provide additional benefits for identifying lesions. Other PET tracers (11C‑Flumazenil (FMZ), α-11C‑methyl-L-tryptophane (AMT)) are clinically applied in special cases only. Both procedures contribute complementary information in multimodal imaging diagnostics.Conclusions: Ictal SPECT and PET are optional diagnostic tools for presurgical assessment in nonlesional epilepsies. They may reverse nonlesional to lesional epilepsy status and identify nonlesional epileptic foci with a fair chance of seizure freedom after epilepsy surgery.
Funding Information
  • Johannes Kepler University Linz

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