PET studies in epilepsy

Abstract

Various PET studies, such as measurements of glucose, serotonin and oxygen metabolism, cerebral blood flow and receptor bindings are availabe for epilepsy. (18)Fluoro-2-deoxyglucose ((18)F-FDG) PET imaging of brain glucose metabolism is a well established and widely available technique. Studies have demonstrated that the sensitivity of interictal FDG-PET is higher than interictal SPECT and similar to ictal SPECT for the lateralization and localization of epileptogenic foci in presurgical patients refractory to medical treatments who have noncontributory EEG and MRI. In addition to localizing epileptogenic focus, FDG-PET provide additional important information on the functional status of the rest of the brain. The main limitation of interictal FDG-PET is that it cannot precisely define the surgical margin as the area of hypometabolism usually extends beyond the epileptogenic zone. Various neurotransmitters (GABA, glutamate, opiates, serotonin, dopamine, acethylcholine, and adenosine) and receptor subtypes are involved in epilepsy. PET receptor imaging studies performed in limited centers help to understand the role of neurotransmitters in epileptogenesis, identify epileptic foci and investigate new treatment approaches. PET receptor imaging studies have demonstrated reduced (11)C-flumazenil (GABAA-cBDZ) and (18)F-MPPF (5-HT1A serotonin) and increased (11)C-cerfentanil (mu opiate) and (11)C-MeNTI (delta opiate) bindings in the area of seizure. (11)C-flumazenil has been reported to be more sensitive than FDG-PET for identifying epileptic foci. The area of abnormality on GABAAcBDZ and opiate receptor images is usually smaller and more circumscribed than the area of hypometabolism on FDG images. Studies have demonstrated that (11)C-alpha-methyl-L-tryptophan PET (to study synthesis of serotonin) can detect the epileptic focus within malformations of cortical development and helps in differentiating epileptogenic from non-epileptogenic tubers in patients with tuberous sclerosis complex. (15)O-H2O PET was reported to have a similar sensitivity to FDG-PET in detecting epileptic foci.

Keywords: Epilepsy; FDG; Neurotransmitter; PET; receptor.

Figure 1

False-negative MR findings in a 30-year-old man with left complex partial seizures. Ictal activity was shown in left temporal area on video/EEG. A. Oblique coronal fast spin-echo T2-weighted MR image (4000/120/4) shows no abnormalities. B. Ictal SPECT scan shows hyperperfusion in left temporal lobe (arrows). Radioactivity ratio between right temporal cortex/left temporal cortex was 1:2.4. C. FDG-PET scan shows hypometabolism in left temporal lobe (arrows). Radioactivity ratio between right temporal cortex/left temporal cortex was 1:0.7. Invasive EEG showed ictal activity in left temporal lobe. After left anterior temporal lobectomy, pathologic diagnosis was hippocampal sclerosis of a mild degree associated with mild cortical dysplasia. Engel’s outcome was class II. Reprinted with permission from American Society of Neuroradiology [16].

Figure 2

FDG-PET image shows extensive hypometabolism throughout right temporal lobe (arrows) (A). FMZ-PET image shows more restricted localization to mesial temporal region in same patient (arrows) (B). Symmetric FMZ distribution in control subject (C). Reprinted with permission from The Society of Nuclear Medicine and Molecular Imaging [62].

Figure 3

¹¹C-WAY-100635 PET in a patient with MRI-negative temporal lobe epilepsy and a right temporal EEG focus. A. T1-weighted axial MRI reveals no structural abnormality. B. ¹¹C-WAY-100635 PET imaging shows asymmetric binding with a decrease in both mesial and lateral structures of the right temporal lobe. Reprinted with permission from Elsevier Limited [86].

Figure 4

Increased AMT uptake in cortical tubers (arrows). A. Clearly MRI hyperintense right perisylvian tuber in a patient. B. Subtly MRI hyperintense left temporal tuber in another patient. Reprinted with permission from John Wiley and Sons [96].

Figure 5

Interictal ¹⁵O-H₂O PET images in a patient with bilateral temporal lobe epilepsia. Note relative hypoperfusion of temporal lobes compared to the whole brain. Reprinted with permission from John Wiley and Sons [103].