Abstracts

Rationale: Although FDG-PET imaging is recognized as important in presurgical evaluation in medically refractory focal temporal lobe and neocortical epilepsy, there has been no investigation as to whether some regions of hypometabolic zones may be of particular importance in defining the seizure-onset zone or potentially epileptogenic zone. This report illustrates with several case examples that techniques isolating the maximally hypometabolic zone may exquisitely identify the seizure-onset zone, sometimes even when not apparent with grid electrodes placed directly on overlying cortex in both MRI positive and negative cases. Methods: Several novel techniques are presented which have proven useful in identifying maximally hypometabolic regions. These include color map LUTs, windowing PET hypometabolism, isocontour thresholding, and restriction of PET to cortex by way of masking with coregistered MRI grey matter segmentation- alone or in combination. Subtle hypometabolic regions are often restricted to a gyrus, and can be difficult to identify with conventional greyscale PET. Color maps and windowing may help identify subtle hypometabolism. Isocontours are useful in 3D lateral hypometabolism visualization. Even within larger hypometabolic regions, identification of maximally hypometabolic regions may exquisitely localize seizure onset zone in gyral depth with or without a lesion even if not apparent a few centimeters away on subdural grids. Volumetric imaging to coregister to T1 MRI helps assure that the hypometabolic region is cortical rather than white matter, and helps in precise placement of intracranial contacts. These techniques are augmented by volumetric 3D or orthographic visualizations. Results: 6 cases are used to illustrate the methods of identifying the maximally hypometabolic regions, the potential value of these regions in iEEG planning, and the value of these localizations in identifying seizure-onset zones. Conclusions: Although the seizure-onset zone may not represent the entire potentially epileptogenic zone, it is unquestionably a critical component of this. These methods therefore may offer important guidance in achieving successful epilepsy surgery outcomes.