Making the Case for Brain ¹⁸F-FDG PET Subtraction in Medically Refractory Epilepsy: A Novel, Useful Tool—Practical Points?

Axial (A), coronal (B), and sagittal (C) views of, from left to right, fluid-attenuated inversion recovery MRI, T2-weighted MRI, diffusion-weighted MRI, subtraction ¹⁸F-FDG PET fused with T1-weighted MRI, and interictal ¹⁸F-FDG PET (in A); ictal ¹⁸F-FDG PET (in B); or z score SSP of ¹⁸F-FDG PET hypometabolism (in C). Thin white arrows show lesion missed on initial MRI. Thick white arrow shows mild hypometabolism. Yellow arrow shows improved metabolism ictally. Blue arrows show cluster of significance in right Rolandic operculum, corresponding to SOZ.

(A) From left to right: 2 basal and left lateral z score SSP views for each of, respectively, preoperative cerebral blood flow ^99mTc-hexamethylpropyleneamine oxime SPECT image, postoperative cerebral blood flow ^99mTc-hexamethylpropyleneamine oxime SPECT image, and postoperative ¹⁸F-FDG PET image. Arrows show ¹⁸F-FDG PET hypometabolism, which improved postoperatively. (B) Subtraction preoperative and postoperative ¹⁸F-FDG PET/MR images displayed in coronal, sagittal, and 3 axial slices. (C) Subtraction ¹⁸F-FDG PET/MR images in all 3 planes showing 2 sites of clusters of significance in left frontal and left parietooccipital lobes. Arrows show 2 potential areas for SOZ. On color scale, yellow-red indicates hypermetabolism and blue-purple indicates hypometabolism.

(A) Three-dimensional SSPs showing significant areas of hypometabolism in left occipital lobe interictally. (B) Three-dimensional SSPs showing no areas of hypermetabolism in left occipital lobe ictally or elsewhere; however, severity of hypometabolism in left occipital region has diminished (pseudonormalization of glucose metabolism). (C) Subtraction ictal–interictal ¹⁸F-FDG PET/MR image showing cluster of significance in left occipital lobe (SOZ).