pre-operative evaluation for epilepsy surgery

1. Dr. Shahnawaz Alam
MCh-Neurosurgery
Moderated by:
Dr. V. C. Jha
HOD, Dept. of Neurosurgery
Evaluation of Patients for
Epilepsy Surgery

2. GOALS OF PRESURGICAL EVALUATION OF PATIENTS WITH
EPILEPSY
• Main Goal of epilepsy Sx: Complete resection (or disconnection) of the cortical areas or
networks responsible for the generation of seizures (epileptogenic zone [EZ]).
• Main goal of the presurgical evaluation: an accurate and comprehensive mapping of
the anatomo-electro-clinical (AEC) network defining the epileptic condition.
• Because the EZ may overlap with the functional (eloquent) cortex; Mapping the extent of
the EZ and its possible overlap with clinically testable functional regions.
• To pre-surgically define the anatomic location of the EZ and its proximity to possible
cortical and subcortical eloquent areas, various non-invasive tools are available.
• They include recorded seizure semiology, scalp EEG, High Resolution MRI, PET,
SPECT, neuropsychological testing, and magnetoencephalography (MEG).

3. Surgically remediable lesional epilepsy syndromes

4. Indications for pre-surgical evaluation

5. CLINICALAPPROACH AND TECHNIQUES USED IN THE
PRESURGICAL EVALUATION
Clinical Approach
• Diagnosis of pharmacoresistant epilepsy/ Detailed history from the patient first
followed by family members or witnesses.
• Later compared with the seizures recorded during prolonged electroencephalographic
and video monitoring.
• Questions regarding birth history, febrile convulsions, head injuries, central nervous
system (CNS) infections, and other possible causes of seizures should be asked.
• Medication trials, doses used, and their side effects should be reviewed. In addition, a
family history should be taken with particular reference to seizures and other
neurological illnesses.
• A neurological examination should uncover focal neurological abnormalities.

6. Seizure Semiology, Lateralisation and Localisation
• Motionless stare with a behavioural arrest is the first evidence of the onset of seizures.

8. • The seizures associated with TLE consist of simple partial seizures without loss of
awareness and complex partial seizures with loss of awareness.
• Auras are more frequent in TLE. Gustatory and olfactory auras are quite
characteristic; epigastric or abdominal auras are considered to be typical of MTLE;
Oro-alimentary automatisms consisting of lip smacking, chewing and swallowing.
• Contralateral arm dystonic posturing and forced contralateral version of the
head and eyes are strongly lateralising features in TLE with specificity more than
90%.
• Psychic auras of fear and dèjàvu are related to the amygdala.
• Post-ictal phenomena, like nose wiping, spitting, coughing and vomiting: seizures
from the non-dominant hemisphere.
• Post-ictal aphasia lateralises the seizure to the language dominant hemisphere.
• Auditory auras; Early secondary generalisation and clonic phenomena involving the
face and hands- seizures from the lateral temporal neocortex.
Semiology of Temporal Lobe Epilepsy

9. PATIENT MANAGEMENT CONFERENCE
• The epilepsy patient management conference is an integral element of any
comprehensive pediatric or adult epilepsy surgery program.
• All of the epilepsy team’s specialists collaborate to provide a multidisciplinary
discussion, to generate hypotheses on the localization of the EZ and its presumed
pathologic cause, and to formulate a set of recommendations to be discussed with the
patient and family.
• Participants include paediatric and adult epileptologists, epilepsy neurosurgeons,
neuroradiologists, functional imaging specialists, MEG specialists,
neuropsychologists, psychiatrists, bioethicists, researchers, social workers, nurse
practitioners, and physicians in training.

10.  The advantages of the tailored progressive approach to epilepsy surgery
evaluation include the following:
 Performance of the needed studies only(fewer studies, less use of resources)
 Faster patient-based decision making
 Decreased health care expenses
 Optimization of outcomes

11. Necessary Techniques For The Localization EZ
• Two most important and necessary studies to be performed on all patients considered
for epilepsy surgery are high resolution MRI and scalp-video EEG monitoring.
 Neuroradiologic Evaluation for Epilepsy Surgery: MRI
Indications
 The onset of partial seizures, at any age.
 The onset of generalized or unclassified seizures in the first year of life or in
adulthood.
 Evidence of a fixed deficit on neurological or neuropsychological examination.
 Difficulty obtaining seizure control with first-line antiepileptic drugs.
 Loss of seizure control or a change in the pattern of seizures.

12. Epilepsy Protocol MRI
• 3T MRI scanners provide high-resolution images and whenever possible should be
preferred over 1.5-T scanners.
• Images should be acquired in an oblique coronal orientation perpendicular to the long
axis of the hippocampus. The entire brain should be included in the field of view to
avoid missing subtle peripheral findings.
• Routine MRI sequences include the following:
 Volumetric T1WI with slices of 1- to 2-mm thickness
 Axial and sagittal high-resolution T2WI with slices of 2- to 3-mm thickness
 Coronal FLAIR sequence in the same plane
 3D-FLAIR sequences
 Coronal T2W GE-sequence.
• Optional Sequences : Magnetization transfer imaging/ T2W relaxometry imaging/
DWI/ MRS
• Interpretation should be done by a subspecialty trained board-certified neuroradiologist
who is active in epilepsy surgery programs.
• In most instances, gadolinium is not necessary unless a tumor or mass lesion is found.

13. Hippocampal Sclerosis
• MTLE is MC form of epilepsy in adults and hippocampal sclerosis or MTS is the main
pathologic process associated with it.
• When hippocampal sclerosis is correctly identified and surgically treated, the rate of
success in achieving seizure freedom is high (60% at 5 years).
• Hippocampal sclerosis is demonstrated as hippocampal atrophy on coronal T1WI and as
increased signal intensity onT2WI.
 Features associated with hippocampal sclerosis are as follows:
 Temporal horn dilatation, caused by volume loss of the hippocampus
 Atrophy of the structures that form the outflow tracts from the hippocampus
(inferiorly, the parahippocampal gyrus; posteriorly, the ipsilateral fornix connected to
the ipsilateral mammillary body)
 Atrophy of the structures indirectly connected with the hippocampus (the remainder
of the temporal lobe, the thalamus, and the caudate nucleus).

14. Hippocampal sclerosis
A. Coronal T1WI showing left hippocampal volume loss with secondary dilatation of the
temporal horn.
B. Coronal FLAIR image showing increased signal in the left hippocampus.

15. Malformations of Cortical Development : 3 Groups
• I: malformations resulting from abnormal proliferation of neuronal and glial cells:
 Microcephaly and macrocephaly
 FCDs without and with balloon cells
 Hemimegalencephaly
 Tuberous sclerosis
 DNET, gangliogliomas, and gangliocytomas.
• II: malformations resulting from abnormal neuronal migration:
 Lissencephaly and
 Heterotopias.
• III: malformations resulting from abnormal cortical organization:
 Polymicrogyrias
 Schizencephaly
 Mild FCDs type

16. Focal cortical dysplasia (FCD)
A and B, Cor T2WI showing hypoplasia of the left temporal pole and loss of gray-white
matter differentiation, in keeping with presence of FCD

17. A. Axial T2WI showing multiple calcified periventricular nodules in the lateral ventricles, which give
rise to the candle guttering sign, typical of tuberous sclerosis. Multiple hyperintense cortical tubers
are also visible.
B. Axial T2WI showing a SEGA in the left frontal horn of the lateral ventricle, which caused
obstruction to the foramen of Monroe; multiple cortical tubers are also visible.
C. Axial (C) and coronal (D) T2WI showing hemispheric asymmetry associated with loss of gray-white
matter differentiation and thickened cortex on the right, in keeping with widespread right hemispheric
malformation (hemimegalencephaly). The hyperintense signal in the left hemisphere represents
normal myelination pattern in a 12-month-old child.

18. • Coronal T1WI (A) and axial T2WI (B) showing extensive bilateral subependymal
nodular gray matter heterotopia.
• Coronal T1WI (C) showing extensive band heterotopia in the right cerebral
hemisphere.
• Coronal T1WI (D) showing schizencephaly that extends to the right ventricle.

19. Tumors and vascular lesions
A. Coronal T1WI showing a hypointense multicystic cortical lesion (arrow) in the left superior temporal
gyrus, consistent with DNET
B. Coronal T2WI showing a right temporal cyst with a mural nodule, consistent with a ganglioglioma.
C. Axial FLAIR image showing extensive increased signal abnormality, centered in the right insular
region and extending into the temporal area, representing a low-grade glioma.
D. Axial T2WI showing the characteristic “popcorn” appearance of a cavernoma in the right temporal
pole.

20. Structural MRI and Cognition in Epilepsy
• Language and memory have been studied extensively in relation to structural imaging in
temporal lobe epilepsy.
• There appears to be a relationship between hippocampal volume and memory
dysfunction.
• Reduced left-sided volumes are associated with impairments in verbal learning and
memory.
• Normal left- sided volumes are associated with greatest postoperative memory decline.
• Right side, reduction in amygdala volume is associated with visual memory loss.
• Patients with temporal lobe epilepsy also exhibit a more global reduction in the volume of
cerebral tissue, most evident when the volume of white matter tissue is measured across
frontal, temporal, and parietal lobe regions, but not occipital lobe regions. This reduction
in volume of white matter is strongly associated with cognitive impairment.
• In patients with temporal lobe epilepsy, increased amygdala volume may be associated
with depression, dysthymia, and psychosis, and decreased amygdala volume may be
associated with interictal aggression.

21. Functional MRI:
• Mapping areas of function to the cortical surface; used to map language, motor
function, memory, and epileptic activity.
• Indirectly detects focal areas of increased neuronal activity by identifying increased
cerebral blood flow when the patient performs specific tasks known as functional
paradigms (i.e., finger tapping in hand motor fMRI, verbal fluency in language fMRI).
• Through echo-planar imaging sequences, a series of scans of the entire brain are generated
that are sensitive to changes in blood oxygen level-dependent (BOLD) signal. The BOLD
signal represents the ratio of oxyhemoglobin concentration to deoxyhemoglobin
concentration.
• These have different signal characteristics onT2WI. A greater concentration of
oxyhemoglobin in comparison with deoxyhemoglobin produces a high BOLD signal and
identifies an area with increased neuronal activity as a result of localized hyperperfusion.

22. • A BOLD signal is created for each region of interest during a specific activity and is
then compared with the signal in the same region in the resting state.
• Signal averaging over multiple acquisitions provides a map of the likelihood that
function is present in this area. This signal map is coregistered with conventional
MR to provide spatial and anatomic resolution.
• Limitations: Area of BOLD activation is greatly influenced by thresholding and can
be widespread or focal; No direct relationship between BOLD intensity and cortical
eloquence; Areas that do not surpass the chosen threshold are not necessarily
functionally inert; The area of BOLD activation might not be crucial to the execution
of the task.

23. • The Intracarotid Amytal (Wada) Test is the traditional “gold standard” investigation to
determine the laterality of language and memory function.
• However, this technique has two limitations: (1) it is an invasive study and carries a
0.6% risk of stroke, and (2) the study is dependent on the internal carotid artery’s being
the sole blood supply to the functional area tested, with no hemispheric crossover.
• Currently, Language fMRI is being increasingly used to determine the laterality of
language dominance.
• Language fMRI shows high levels of concordance with the Wada test in lateralizing
language function. Because it is cheap, non-invasive, and repeatable, many centers have
abandoned the Wada test infavour of language fMRI for lateralization of function.

24. Functional magnetic resonance images
• Unthresholded ictal statistical parametric maps for verbal fluency task, overlaid on T1WI.
• Red indicates positive activation, and blue indicates negative activation.

25. Electroencephalography fMRI:
• EEG-fMRI is a multimodal imaging technique that can be used to localize the region of
the brain responsible for generating epileptiform discharges. This is done by mapping
changes in hemodynamic BOLD levels associated with interictal and ictal epileptiform
discharges.
• EEG-fMRI is a non-invasive technique that has the significant advantage of combining
the high spatial resolution of fMRI with the excellent temporal resolution of EEG.
• Limitation: Requirement for epileptiform activity during the scanning, which leads to a
low yield in selected patients.
• A new technique (Grouiller’s method) addresses this limitation by incorporating voltage
maps of epileptic spikes obtained previously during long-term EEG recordings into the
EEG obtained in the scanner.
• Typically studies last between 10 and 40 minutes; Concordance between BOLD signal
and electroclinical localization of the epileptogenic zone is reasonable in 40% to 60% of
patients.

26. Diffusion-Weighted Imaging
• Maps the diffusion of water in biologic tissues, so that each voxel has an intensity that
reflects the best measurement of the rate of water diffusion. DWI is used to delineate the
white matter pathways of the brain through a technique called tractography.
• Water diffusion anisotropy (direction) in the white matter is defined by axonal alignment.
Water diffuses preferentially in a direction parallel to the longitudinal axis of the axon,
and diffusion is restricted perpendicular to the axis.
• Each voxel can therefore be expressed mathematically as a diffusion ellipsoid or tensor.
The long axis of adjacent tensors can be “tracked” to progressively reconstruct the 3D
orientation of nerve fibers that represent white matter connectivity.
• The translation of the tensors into neural trajectories can be achieved through various
algorithms, which can be broadly classified as deterministic and probabilistic. The most
common approach used clinically is deterministic line propagation or streamline
techniques, whereby neural connections are mapped in at least two arbitrary regions of
interest in 3D space.

27. Principles of tractography
A. Diffusion ellipsoids (tensors). When there is no
directionality, the fractional anisotropy is zero
(spherical). A typical tensor of a white matter tract is
cigar-shaped. When there are crossing fibers, the
ellipsoid becomes flattened, resulting in pancake-shaped
tensors.
B. Tracking starts at a pixel, and continues along the
ellipsoids as long as the adjacent vectors are strongly
aligned.
C. Axial image of color fractional anisotropic map, showing
posterior corpus callosum.
D. Tractography of the left arcuate fasciculus and
corticospinal tract.

28. • Tractography has been clinically applied most frequently to the surgical treatment of
brain tumors. The corticospinal pathway is the most commonly generated tract for the
treatment of tumors that lie close to the motor cortex. There is now good experience in
the use of tractography exported into neuronavigation systems to aid the decision-
making process during tumor resection.
• In the context of epilepsy surgery, DTI is obviously applicable to lesional cases close to
eloquent cortex tissue. However, in nonlesional cases, DTI can help in evaluating the
relationship between the epileptogenic area and the subcortical fibers. This is beneficial
not only for surgical planning but also for neurophysiologic purposes to better
understand the possible connectivity underlying the electrical spread of the seizure.

29. Magnetic resonance spectroscopy (MRS) :
• In patients with seizures, the metabolic work of brain cells increased, which causes the
demand for oxygen and nutrients to exceed supply. MRS detects this imbalance,
identifying abnormal accumulation of lactate and N-acetyl aspartate (NAA).
• From a surgical perspective, MRS has two main areas of application. First, it may be
useful in the diagnosis of an epileptogenic lesion. In difficult cases, 1H MRS has a
potential role in the preoperative differential diagnosis and can improve the accuracy and
the level of confidence in differentiating a tumor from a FCD.
• Tumor : Reduced levels of NAA(neuronal marker ) leads to decreased NAA/creatine
ratios/ Increased levels of choline leads to increase in the choline/NAA and
choline/creatine ratios/ Minor changes in creatine levels.
• Decreased NAA/creatine ratios can also be a common finding in FCD; however, the
relatively normal choline/creatine ratio may help to distinguish FCD from a
neoplasm.

30. MULTIMODALITY IMAGING IN EPILEPSY SURGERY
• 3D-Multimodality imaging (3DMMI) is the use of different tools that provide distinct,
complementary information to solve a common complex problem.
• The fundamental concept is that the integration of different data sets into a single 3D
platform.
• Optimal for the evaluation of the spatial concordance of a site of seizure localization
established through different modalities, as well as the relationship of the structural,
functional and electrophysiologic changes to the anatomic features in the area.
• It also allows the determination of the proximity of the epileptogenic zone to eloquent
cortex tissue or the functional deficit zone.
• Steps to generate 3DMMI data: Image acquisition/Co-registration/Segmentation of region
of interest/3D visualization as surface or volume renderings.

31. • In the field of pediatric epilepsy, the use of FDG-PET, DTI, and magnetic source
images has significantly improved lesion detection and localization.
• SPECT Coregistered with MRI (SISCOM); imaging was coregistered with the use of
a Unix-based workstation and commercially available software package (Analyze) and
then downloaded onto a neuronavigation system for use in the operating room.
• The incorporation of robust vascular imaging into the anatomic imaging is a
prerequisite to the technique of stereo-electroencephalography (SEEG). It is possible
by 3DMMI.
3D-visualization of patient data in EpiNav software:
A. Models of scalp (white), volume rendering of brain
(brown), and segmentation of tumor (red).
B. Addition of hand motor area (dark green) and foot motor
area (light green) on fMRI, corticospinal tractography
(blue), and implanted electrodes (yellow).

32. • The generation of 3DMMI currently takes place in three different ways:
1. Basic planning on commercially available neuronavigation systems (StealthStation
S7 Navigation System, Medtronic, Minneapolis; Brainlab products, Brainlab,
Feldkirchen, Germany)
2. Specialized planning software as an adjunct to neuronavigation software
(StealthViz planning station, Medtronic, Minneapolis; iPlan, Brainlab)
3. Standalone specialized planning software packages (e.g., Amira, Visualization
Sciences Group, Bordeaux, France)
• Neuronavigation systems offer the most user-friendly and the simplest experience,
although they are limited in their functionality with regard to data processing and
analysis, visualization, and presentation.

33. 3DMMI
Volume rendering of cortex (gray), displayed in
AMIRA software with the following associated
modalities: focal cortical dysplasia (FCD) (red),
hypometabolism on fluorodeoxyglucose positron
emission tomography (pink), hand motor area on
functional magnetic resonance imaging (fMRI)
(green), corticospinal tractography (purple), veins
(cyan), and language fMRI (orange).
Planning tools in epilepsy
Stereo-electroencephalographic planning in EpiNav
software with volume rendering of cortex (brown), veins
segmented from magnetic resonance venogram (cyan), and
implanted depth electrodes (yellow).

34. • Interventional MRI (iMRI) is an operating modality that is used in an MRI facility. It
allows the surgeon to acquire scans intraoperatively before head closure.
• Benefits include determination of the performed resection, detection of residual lesion, and
reregistration of neuronavigation software to correct for brain shift.
Combined use of tractography and interventional
MRI during anterior temporal lobe resection
• View down the microscope during the approach
of the temporal horn of the ventricle for access to
the mesial temporal structures, with optic
radiation tractography (yellow outline) and model
of the ventricle (white outline) shown.
• The solid lines refer to the structure in the focal
plane, and dotted lines refer to the maximum
extent below this. The blue dotted line shows the
line of resection anterior to the display of the
optic radiation.
• A, Ventricle not opened. B, Ventricle opened and
hippocampus visualized.

35. Scalp-Video Electroencephalographic Monitoring
• Prolonged video-EEG recordings in a dedicated epilepsy monitoring unit are needed to
confirm the diagnosis of epilepsy (through interictal and ictal EEG epileptic patterns)
and generate hypotheses on the network structures that may be involved in seizure
generation and progression (through analysis of the captured seizure semiology) leading
to the formulation of a clear AEC hypothesis.
• It is helpful to the physicians working in the EEG/video monitoring unit to have the MRI
scan before the monitoring is done. The information from the history, neurological
examination, and MRI scan is needed in the planning of the monitoring.
• Although a lesion seen on MRI is very helpful in the epilepsy surgery evaluation and
may correlate with a good surgical outcome, a normal MRI does not by itself exclude a
patient from epilepsy surgery; it does, however, make the presurgical evaluation
significantly more complicated and expensive.

36. INVASIVE EVALUATION TECHNIQUES
• In patients with MRI-negative epilepsy, non-invasive techniques may point to the general
area of epileptogenicity or identify the epileptic network but may not accurately localize
or map the EZ and its function.
• As a result, direct cortical recording and electrical stimulation mapping is indicated for
these patients.
• Indications:
 MRI-Negative cases: No cortical lesion in a location that is concordant with the
electroclinical or functional hypothesis generated by the video-EEG recordings.
 There are two or more anatomic lesions with the location of at least one of them being
discordant with the electroclinical hypothesis, or both lesions are located within the same
functional network and it is unclear if one or both of them are epileptic.
 The generated AEC hypothesis (MRI-negative) involves potentially eloquent cortex.
 In these instances, an invasive evaluation would lead to the formulation of a clear
resective surgical strategy. The recommendation for invasive monitoring and its type
should always be made after a detailed discussion of all the findings of the non-invasive
tests during the patient management conference.

37.  Subdural Grid:
• Extra-operative mapping with the SDG
method (which includes SDGs and strips):
Comprehensive anatomic coverage of cortical
surfaces, which allows accurate anatomic
electrical and functional mapping i.e. clear
cortical lesions (in particular tumors).
• Limitations of SGDs include inadequate,
partial, or incomplete intrasulcal, deep brain
(e.g., insular, posterior orbitofrontal), and
interhemispheric (e.g., cingulate gyrus)
coverage and the relative difficulty of
multilobar, three dimensional, and large-
functional network sampling.

38.  Stereo-Electroencephalography (SEEG)
• The principle of SEEG is based on AEC
correlations, with the main aim being to
reconstruct the 3D-spatial-temporal
organization of the epileptic discharge
within the brain based mainly on seizure
semiology.
• The most important characteristic of SEEG
methodology is that it enables precise
recordings from deep cortical and
subcortical structures and multiple non-
contiguous lobes, as well as bilateral
explorations, while avoiding the need for
large craniotomies.
• The technical complexity regarding the
placement of SEEG depth electrodes may
have contributed to its limited widespread
use.

39. Choice of Invasive Method

40. Magnetoencephalography (MEG)
• Direct, noninvasive and painless neurophysiologic technique to study the brain; Involves no
external magnetic field, x-rays, or radioactivity; also known as magnetic source imaging
(MSI).
• Based on measuring magnetic fields primarily associated with the summated postsynaptic
intradendritic electric currents subtending normal and pathologic cerebral processes that
are reflected outside of the skull.
• Parallel orientation of the dendrites (cortical pyramidal cells) and Synchronous firing is the
critical prerequisite for a spatial and temporal summation to be detected by the
supersensitive sensors used in MEG systems.
• Because the strength of the magnetic fields produced by the brain is extremely low, very
specialized instrumentation is required to detect these signals.
• These current are associated with magnetic fields
(Fundamental laws of physics i.e., Maxwell’s equations) that
are recorded using supersensitive magnetic sensors.

41. • These sensing devices contain small coils (or chips) that function as flux transformers and
are coupled to superconducting quantum interference devices (SQUIDs) that operate on two
phenomena of quantum physics: superconductivity and tunneling.
• Most modern systems include more than 300 of these specialized sensors arranged in a
helmet shaped configuration. By analyzing the complex patterns of the signals recorded by
the sensors, the location, strength, and orientation of the sources can be estimated.
• MEG uses extensive spatial sampling, enabled by hundreds of sampling locations
surrounding the brain, in contrast to the 20 to 30 electrodes used in traditional routine
electroencephalography (EEG).
• This sampling volume not altered by the intervening tissues (CSF, meninges, skull, and
scalp) i.e. the tissues surrounding the brain are “transparent” for magnetic fields; make MEG
a superior technique for localizing the brain’s activity very accurately.
• This is particularly helpful when dealing with a complex clinical cases involving altered
anatomy, as in postoperative and posttraumatic scenarios in which EEG signals are distorted
and may provide misleading localization.

42. • Unlike EEG, which measures an amplified potential difference between two electrodes
placed on the scalp, MEG measures summated, very weak magnetic fields.
• SQUIDS, used to measure these fields, require cooling to attain the state of
superconductivity. This is currently achieved by their immersion in liquid helium,
which attains a temperature near absolute zero (−269°C).
• Compared to EEG, the advantages of MEG include that it is free of biologic
references, requires no electrodes, and is able to detect a smaller activated area
(about 6 cm2 versus >10 cm2). Also, its signals are not distorted by the skull or other
intervening tissues.
• Limitation: immobile, too much expensive, susceptible to metallic and movement
artifacts, labor intensive data analysis procedures.

43. • MEG creates neuronavigational maps that can be used by surgeons in real time during
a surgical procedure, and that assist in delineation of parts of the brain to preserve or
remove.
• The current cost of the system, with a magnetically shielded room, is close to $3
million. In the United States, an annual service contract ranges from $80,000.
• Provides interictal recordings and identifies an irritative zone.
• Patients with a negative scalp EEG should be referred for a MEG study.
• MEG can localize any eloquent cortices; Clinically established functional mapping
modalities are language, somatosensory, motor, auditory, and visual.

44. • A MEG tracing from the right temporal region (B) contains multiple spikes (marked by red arrows), one of which
can be better appreciated spatially on the head panel (C) in the area marked by the circle.
• D and E, Morphology of the spike can fully be explored (D), and its corresponding field projected on the right
side of the head (E).
• The accepted position of the model of the spike’s most prominent peak source (i.e., dipole) in three radiologic
projections is shown in panels F, G, and H.

45. Possible Benefits of MEG in Presurgical Evaluation
 Localize eloquent cortices of interest noninvasively in patients without structural
abnormalities.
 Establish spatial relations of the lesion(s) with eloquent cortices noninvasively.
 Detect the functional tissue within the tumor (e.g., diffusely growing gliomas).
 Identify displaced anatomic landmarks (central sulcus, sylvian fissure, etc.).
 Assist in choosing an optimal surgical trajectory.
 Overall, define the key elements of a comprehensive neuronavigational map as a
prerequisite for planning an optimal surgical trajectory and safe intraoperative
navigation and operation.

46. Nonlesional extratemporal epilepsy
• In consideration of epilepsy surgery,
A standard presurgical evaluation
that included 1.5-T and 3.0-T brain
MRI with epilepsy protocols, routine
EEG, video-EEG,
neuropsychological testing (NPT),
FDG-PET, and MEG-EEG.
• There were no structural
abnormalities on 1.5- and 3.0-T brain
MRI with epilepsy protocols (A) and
a normal FDG-PET (B).
• However, there were positive findings from an MEG study (D), indicative of significant
cerebral dysfunction and epileptic potential expressed through the right inferior parietal
lobule, and from a congruent 3-T MRS (C and E) indicative of significant metabolic
abnormality in the right inferior parietal lobule.
• Yellow lines seen on the scout image in panels C and E outline the estimated position of the
central sulcus.

47. • Focal epilepsy, the most common of seizure disorders, may be amenable to surgery if
the seizure onset zone can be identified; Localization, therefore, is the key to
surgically remediable epilepsy syndromes.
• In lesional epilepsy cases, this can be relatively straightforward with standard MRI. In
nonlesional cases, however, and those with discordant features, alternative techniques
such as SPECT are sometimes used to localize seizure onset.
• SPECT is an imaging technique that assesses cerebral blood flow by deposition of a
metabolized radiopharmaceutical in the brain. Technetium 99-m ethyl cysteinate
diethylester (ECD; Neurolite) or hexamethyl propylene amine oxime (HMPAO;
Ceretec) is distributed to brain tissue in proportion to cerebral perfusion, is deposited,
and remains stable for up to 4 hours after injection.
• This deposition is used to indicate areas that are either hyperperfused during a seizure
(called ictal SPECT) or hypoperfused after or between seizures (called postictal or
interictal SPECT).
• SPECT is a very time- and resource-intensive study.
Single-photon Emission Computed Tomography (SPECT)

48. SISCOM
• Subtraction of a patient’s interictal SPECT from the ictal SPECT image, with subsequent
fusion to an MRI, has been termed SISCOM.
• This methodology is thought to enhance the anatomic accuracy of the SPECT image as
well as demonstrating more accurately the focus of hyperperfusion associated with the
seizure.
• Further, it enhances surgical planning because of the computer-generated estimation of
the SPECT abnormality projected over the high-resolution anatomy of the MRI; aid the
consensus decision-making process in epilepsy surgery.
• A, Interictal, or baseline SPECT. B, Ictal SPECT. C, The ictal-interictal subtraction image (masked to exclude extracerebral activity.
• The tracer was injected 21 seconds following onset in a seizure lasting 5 minutes. The subtraction image shows increased tracer
deposition, and hence blood flow, in the left temporal lobe along the margin of the prior resection. The assumption is that seizures
continue to arise in the left temporal lobe.

49. • More recent advances in SPECT seizure imaging involve statistical comparisons
between the patient’s SPECT scans and a set of paired SPECT scans from normal
subjects.
• Statistical parametric mapping (SPM) provides a general framework for comparing
groups of images. Recently developed techniques to perform this statistical testing with
ictal and interictal SPECT images include ictal SPECT analysis by SPM (ISAS) and
statistical ictal SPECT coregistered to MRI (STATISCOM).
• These techniques seek to determine any significant perfusion differences between a
patient’s scan and normal variations seen within a neurologically normal population.
• STATISCOM can potentially further improve the accuracy in identifying the
seizure onset zone compared with SISCOM.

50. • Statistical parameter mapping (SPM)-based ictal SPECT analysis (statistical ictal SPECT coregistered MRI
(STATISCOM) from a patient with left temporal lobe epilepsy.
• These SPM-based methods identify statistically significant differences between the ictal and interictal SPECT
scans in a patient compared with a group of paired SPECT scans from normal volunteers.

51. • Depending on the location of the epileptogenic zone, resective epilepsy surgery frequently
carries a risk for cognitive decline, and Wada testing is used to predict the nature and
degree of this risk.
• Originally developed in the 1940s by John Wada and Theodore Rasmussen to determine
hemispheric language dominance, the procedure remains the “gold standard” in this
regard.
• Wada testing involves, primarily, assessment of language and memory during the
period of hemianesthesia. A comprehensive neuropsychological evaluation performed,
ideally, within several weeks before the procedure provides the examiner with information
regarding baseline language and memory, which aids interpretation of language and
memory performance during the period of hemianesthesia.
• The Wada procedure was developed using sodium amobarbital, and this remained the
primary anesthetic used in Wada testing.
Intracarotid Amytal (Wada) Test

52. • Scalp electroencephalogram (EEG) leads may be applied to assist in monitoring the
effect of hemianesthesia and, when needed, to ascertain the presence of seizure activity
or whether the patient is in an awake or sleep state.
• Before the anesthetizing agent is administered, carotid angiography is performed to
determine the presence or degree of cross flow to the contralateral hemisphere, the extent
of perfusion of the posterior cerebral artery (PCA), and potentially dangerous
neurovascular patterns that would result in perfusion to the brainstem.
• The catheter that was used for angiography remains at the proximal segment of the
internal carotid artery (ICA) in preparation for injection of the anesthetic agent.
• Alternate anesthetic agents such as etomidate, propofol, secobarbital sodium, and
methohexital.

53. • Amobarbital is considered a short-acting drug, with peak effect lasting 4 to 8
minutes; dose: 100-125 mg range.
• Both methohexital and etomidate are shorter acting relative to amobarbital. The
absence of prolonged sedation has been accepted as a welcome change; however, a
shorter acting agent provides less time for testing.
• Risks of Wada testing have been estimated using cerebral angiography risk data and
therefore include stroke, femoral neuropathy, internal artery spasm, and arterial
dissection; Risk factors for complications included older age for stroke and dissection
and younger age for seizures.

54. References:
• Youmans and Winn neurological surgery 7th edition
• Ramamurthi & Tandon's textbook of neurosurgery 3rd edition
• Internet
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