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Abstract
Epilepsy is a chronic neurological disorder manifesting recurrent unprovoked epileptic seizures. About 20~30% of epilepsy patients are resistant to antiepileptic medications. These patients suffer from high risk of physical injury, unemployment, marital problem, and psychological stress. Epilepsy surgery is the firstly recommended treatment modality for the patients with medically intractable epilepsy. Presurgical evaluation is the most important process for performing epilepsy surgery. The ultimate goal of the presurgical evaluation in patients with medically refractory partial seizures is the localization of the epileptogenic zone and the resection of which is also both necessary and sufficient to render the patient seizure-free. The localization of the epileptogenic zone derives from a hierarchical synthesis of localizing data independently obtained from clinical, electrographic, neuroimaging, and neuropsychological examination. In addition, closely related to the goal of localizing the epileptogenic zone is the significant need for anticipating the risks of functional deficits that could derive from the surgical resection. Mesial temporal lobe epilepsy (TLE) is the best candidate for epilepsy surgery. Anterior temporal lobectomy with amygdalohippocampectomy is a surgical treatment method for mesial TLE and its seizure-free rate (SFR) is 60~90%, whereas one-year SFR of antiepileptic drug treatment for mesial TLE is 10~20%. Cortisectomy is a surgical method for extratemporal epilepsy and its SFR is about 40~70%. Corpus callosotomy is a partial or complete division of corpus callosum for preventing seizure propagations between right and left hemispheres and is effective for controlling atonic seizures. The variation of postsurgical seizure outcomes is related to the qualities of epilepsy surgery program, presurgical evaluation and surgical techniques. For the good surgical outcome, the epilepsy surgery program should include neurologist, neurosurgeon, neuropsychologist, neuro-radiologist and neuro-nuclear medicine specialist for a comprehensive team approach.
Figures and Tables
Figure 1
Left hippocampal sclerosis. T2 weighted (left) and fluid attenuated inversion recovery (FLAIR, right) MR images show decreased volume and increased signal in left hippocampus (arrow) in a patient with left mesial temporal lobe epilepsy. MRI images were obtained from Samsung Medical Center.
Figure 2
MRI-PET co-registration. A 7 year-old girl has suffered from frequent supplementary motor area seizures occurring several times per a night. Her brain MRI (A) showed no abnormality whereas brain FDG-PET (B) revealed a definite hypometabolism on left medical frontal region (arrow). Fused image (C) of MRI and FDG-PET could localize the hypometabolic zone on the patient's MRI. MRI and FDG-PET images were obtained from Samsung Medical Center.
Figure 3
Transmantle dysplasia right frontal-axial T2 FSE (D) and axial magnetization prepared rapid gradient echo (B), a thin section volumetric T1-weighted sequence (right) obtained with a 3T PA MRI showing a subtle right frontal cone-shaped region of increased T2 signal that begins at the ventricular margin and extends to the depth of a sulcus (see arrowheads in D). The lesion corresponds to a more subtle region of decreased T1 signal (arrowheads, B). On close scrutiny of the overlying cortex, increased T2 signal (arrows, D) and increased T1 signal (arrows, B) with blurring of the gray-white junction is identified. Previous high resolution 1.5T MRI obtained with a regular head coil did not show the lesion (A, T1-weighted image, C, T2-weighted image). Due to different imaging protocols, the two images are angled slightly differently and have different slice thickness (1.5T images courtesy Dr. P. Due Tⓒ™nnessen, Dept. of Radiology, Rikshospitalet Olso, Norway). This figure was quoted on the permission of Dr. P. Ellen Grant.
Figure 4
24-hour video-EEG monitoring unit. In the video-EEG monitoring room, patients' EEG and behavior are being recorded and monitored by Vanguard EEG system and trained EEG technicians. If a patient starts having a seizure, a technician should run into a monitoring room and perform a seizure interview, and may inject a radiotracer for ictal SPECT study. This picture was obtained from Epilepsy Monitoring Unit in Samsung Medical Center.
Figure 5
Ictal scalp EEG recorded during clinical seizures shows rhythmic discharges (arrow) on left temporal lobe with many muscle artifacts (arrow head). The EEG montage in left column indicates left hemisphere by odd numbers whereas right hemisphere by even numbers. This patient has a left hippocampal sclerosis on her brain MRI. She has been seizure free after her anterior temporal lobe and amygdala/hippocampus were resected. The EEG data were obtained from Samsung Medical Center.
Figure 6
Ictal SPECT and SISCOM. Ictal SPECT (A) shows increased cerebral blood flow on right anterior frontal region (arrow). SISCOM (B) shows very well localized ictal hyperperfusion (arrow) on right hippocampus and insular cortex in a patient with right mesial temporal lobe epilepsy. Ictal SPECT and SISCOM images were obtained from Samsung Medical Center.
Figure 7
Intracranial electrodes. (A) is a 1×8 subdural strip electrode, (B) is a 4×8 subdural grid electrode and (C) is a 1×8 depth electrode. Subdural electrodes are placed on cortical surface whereas a depth electrode is placed on deeper brain structures such as bilateral hippocampi and interhemispheric medial frontal regions by piercing cerebral cortex and white matter with either stereotactic frames or with a frameless stereotactic technique.
Figure 8
Subdural grid electrode insertion. (A) shows subdural grid electrodes (4×8) placed on right frontoparietal cortex. (B) demonstrates the location of subdural grid (4×8) and strip (1×8) electrodes on the patient's 3D brain by a CT-MRI co-registration technique. The images were obtained from Samsung Medical Center.
Figure 9
Intracranial cortical EEG. This patient is a 7 year-old girl who had suffered from frequent bilateral tonic seizures with preserved consciousness. Well localized EEG seizure discharges (low amplitude rhythmic fast activities) were recorded during clinical seizures on left surperior frontoparietal regions of subdural grid electrodes. Intracranial EEG recording and a functional map by electrical cortical stimulation are necessary for determining a resection margin of neocortical epilepsy. The intracranial EEG data were obtained from Samsung Medical Center.
Figure 10
Decision making cascade for intractable epilepsy patients
mTLE: mesial temporal lobe epilepsy, Neo.: neocortical, Gen.: generalized, HS: hippocampal sclerosis, Uni.: unilateral, Bi: bilateral, FDG-PET: 18F-fluorodeoxy glucose positron emission tomography, hypom: hypometabolism, electr: electrode, ipsi: ipsilateral to epileptic focus, contra: contralateral to epileptic focus, MST: multiple subpial transection, ECoG: intraoperative electro-corticography, PKC: paroxysmal kinesogenic choreoathetosis, Ipsi ≫ contra: Ipsilateral hippocampal seizure origin is much more frequent than contralateral origin. Ipsi ≈ contra: Ipsilateral hippocampal seizure frequency is similar to contralateral seizure frequency. TIA: transient ischemic attack, ATL & AH: anterior temporal lobectomy & amygdalohippocampectomy.
Table 2
Contents of presurgical evaluation
Performed invariably: almost always obtained prior to epilepsy surgery. Performed variably: available at most epilepsy centers, used in selected candidates. Performed in selected centers: not widely available. MRI: magnetic resonance imaging, PET: positron emission tomography, SPECT: single photon emission computed tomography. SISCOM: subtraction ictal SPECT co-registered to MRI, MRS: magnetic resonance spectroscopy, MEG: magnetoencephalography, MRI special study: volumetry, 3-D rendering, gyroscan, etc.
Acknowledgement
This work was supported by a grant(03-PJ1-PG3-21300-0033) of the Good Health R&D Project, Ministry of Health & Welfare, Republic of Korea.
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