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Surgical Imaging Figure 5: Magnetoencephalography Left MEG channels EKG R L R L A PP A


Fp1–F3 F3–C3 C3–P3 P3–O1 Fp1–F7 F7–T3 T3–T5 T5–O1 Fz–Cz Cz–Pz Fp2–F4 F4–C4 C4–P4 C4–O2 Fp2–F8 F8–T4 T4–T6 T6–O2


R LL R


3.00 pT–75.00 u 0.3000 s


3.00 pT–75.00 u 0.3000 s


3.00 pT–75.00 u 0.3000 s


This 35-year-old man presented with long-standing generalized tonic–clonic seizures with magnetic resonance imaging revealing a subtle cortical dysplasia in the right frontal lobe. Left: A magnetoencephalography (MEG) study with simultaneous electroencephalography recording demonstrated frequent high-amplitude spike and slow-wave discharges that were maximal in the right frontal region (right panels); manual single equivalent current dipole fitting was performed on these spikes (shown in orange) and dipoles (shown as yellow triangles on all MEG images) clustered in the right frontal regions. The patient underwent a lesionectomy and was seizure-free after surgery. EKG = electrocardiogram; pT = pico-testas; s = seconds; u = units. Adapted from Chang et al., 2009,56


with permission.


recent study showed that in a series of patients with MRI-negative but PET-positive lesions in TLE, 71 % were Engel Class I at one year.38


Given


the cost-effectiveness of FDG-PET, it is a useful study to select for surgical candidates and guide decision-making when MRI and EEG are not concordant or localizing.


Much interest has been generated over the use of specific receptor ligands that confer increased uptake in seizure, such as 11C-alpha-methyl-l-tryptophan (11C-AMT) and 18F-fluoro-benzamidoethylpiperazine (18F-MPPF) (seratonergic tracers), 18F-fallypride (dopaminergic tracer), and 11C-flumazenil (GABAergic tracer).21


For instance, Chugani and colleagues reported that in 30


and transferred to SPECT scanners to acquire the brain scan. SPECT imaging has the advantage of capturing the dynamic ictal process and being less subject to movement artifacts (see Figure 4B).21


Many studies have assessed the sensitivity and specificity of SPECT imaging in revealing epilepsy and have reported favorable results. A meta-analysis showed that the highest sensitivity reported in ictal SPECT is 97–100 %, postictal SPECT 75–77 %, and interictal SPECT 43–44 %.40,41


pediatric


This may indicate that uptake of specific tracers can identify specific pathologies and have good prognostic value. PET scanning with ligand-specific tracers may prove to be a valuable tool in advancing our knowledge of the basic mechanisms of epileptic disorders.


patients with MCD who received 11C-AMT-PET imaging, increased AMT was found in all five patients with type IIB dysplasia and all three patients with polymicrogyria and heterotopia; all of these patients had good surgical outcome.39


Right MEG channels


The different radiotracers may confer different detection rates in different types of epilepsy. For instance, in TLE, HMPAO and ECD have shown similar sensitivities in detecting the epileptogenic region, but HMPAO is superior to ECD in terms of both sensitivity and degree of hyperperfusion in neocortical epilepsy.42


Despite the high sensitivity


of ictal SPECT, several studies have questioned the specificity of SPECT imaging, especially when SPECT does not correlate with EEG data.43,44 In one study, SPECT erroneously localized supplementary motor area seizures to the bilateral cingulate.43


Single Photon Emission Computed Tomography SPECT uses photon-emitting radioisotopes attached to molecules to label brain regions of interest, mainly areas of hypermetabolic activity during ictal activity. The images are captured using relatively fast and low-resolution gamma cameras. The majority of studies in epilepsy use technetium-99m hexamethylpropylene amine oxime (99mTc-HMPAO) or technetium-99m ethyl cysteinate diethylester (99mTc-ECD), both of which are lipophilic compounds that get irreversibly trapped in the epileptogenic hyperemic region at the time of the seizure.21,31


Because


of the rapid initial tracer uptake and distribution, the radiotracer can be injected at the time of seizure onset. The patient can then be sedated


172


SPECT should be used for partial seizure evaluation but may not be useful for generalized seizures.


In another study, patients with mesial TLE were found to have localized hyperperfusion not limited to the temporal lobe but also in the basal ganglia, which may reflect more of the ictal dystonia caused by seizure propagation rather than area of seizure onset.45


In addition, other brain


regions have been noted to show SPECT changes in TLE, including hyperperfusion in the posterior frontal lobes, parietal lobes, and cerebellum, and hypoperfusion in the bilateral frontal lobes.46


These


differences may indicate inter-subject differences in functional network connectivity or may reflect different temporal evolution of an ictal event based on when the tracer was injected. A large TLE series attempted to examine this very question of evolving dynamics of the seizure network


US NEUROLOGY


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