Preoperative Assessment of Epilepsy and their localization, clinical semiology and Radiological evaluation MRI imaging, Video EEG MEG SPECT PET and patient management conference explained in simplified way

1. Pre-operative assessment of
Epilepsy- Clinical, Radiological,
EEG and MEG
Dr Fakir Mohan Sahu
MCh Resident
AIIMS Bhubaneswar
17/06/2021

2. Learning Objectives
• What is Refractory/ Drug resistance Epilepsy
• Goal of Pre-surgical evaluation
• Clinical Semiology
• Radiological Assessment
• Electroencephalography (EEG)- Scalp/Video
• Magnetoencephalography (MEG)
• Invasive Vs non-invasive assessment
• Recent Advances in Preoperative Epilepsy assessment

3. Introduction
• Epilepsy fail to respond to adequate antiepileptic treatment- 25% to 30%
• Sx success rate app. 75% (site & type of surgery and underlying etiology)
• Reduction in risk-
-a number of avoidable seizure related deaths,(Drowning, motor vehicle accident)
-fatal status epilepticus, & sudden unexpected death in epilepsy (SUDEP)
• In children, appropriate timing for surgical procedures is critical,
(lack of seizure control may interfere with consolidation of cognitive and motor functions in the developing brain)

4. Medically intractable (refractory) epilepsy
• When satisfactory seizure control cannot be achieved (ILAE)
-with any of the potentially available effective antiepileptic drugs (AEDs)
-alone or in combination, at doses or levels not a/w unacceptable side effects.
• First step of evaluation -to confirm the proper diagnosis and appropriate medical treatment has been utilized
• Poor response to medical treatment-
Noncompliance
Presence of pseudo-epileptic seizures alone or combined with epileptic ones
Incorrect classification of seizures & incorrect pharmacologic treatment.

5. Patient Perceptions
• Self-assessment of quality of life is an important step in evaluating the
patient’s perception of their disease.
• Some patients seek surgical treatment- for reasons other than medical
intractability
-intolerable side effects of AEDs,
-women who desire to get pregnant (concerned potential teratogenic)
-avoidance of the social stigmata
• Questionnaires QOLIE-31 for adults, and QOLIE-48-AD for adolescents

6. Goal of Pre-surgical evaluation
• Accurate and comprehensive mapping of the Anatomo-electro-clinical(AEC)
network defining the EZ
• Its possible overlap with clinically testable functional/ eloquent cortex
• To generate a “surgical diagram” depicting
 Epileptogenic region (ER)---Location, Extent
 Critical cortex ( CC)
• Surgical resection = ER - CC
• The MC location of seizure onset in adults -Temporal lobe,
Medial temporal lobe (hippocampus).
most amenable to surgical cure.

7. Classification of Presurgical evaluation
• Mandatory noninvasive – “universal
access”
 Clinical semiology and Exam
 Scalp EEG
 Imaging MRI
• Optional Noninvasive – “Limited Access “
Video EEG
Magnetoencephalography (MEG),
EEG-fMRI,
Nuclear imaging (PET,SPECT )
Neuropsychological testing
No single test adequately defines the epileptogenic region
Invasive test
invasive EEG
Depth, strip, grid electrodes
Wada (intracarotid amobarbital) test

8. Definition of abnormal brain areas

9. Clinical Semiology
• Temporal Lobe Epilepsy- an epigastric aura, followed by a quiet period of unresponsiveness
with staring, lipsmacking (oral automatisms).
-Picking at sheets or clothes (manual automatisms),
- contralateral dystonic posturing
-Postictal confusion and lethargy.
Dominant hemisphere- delayed recovery of language, often with transient aphasia on testing.
• Frontal lobe seizure-will occur from sleep with no warning,
-restlessness and/or prominent bilateral limb movements (bicycling/ asymmetric tonic posturing),
-end quickly with immediate recovery; this may recur several times in one night
• Occipital lobe seizures -visual aura, and may progress (due to electrical spread) into a temporal
lobe or frontal lobe type of seizure.
• Parietal lobe seizures are the least common, may have a sensory aura,
and tend to mimic frontal lobe seizures

10. Semiology Frontal Vs Temporal lobe

11. LANGUAGE ABNORMALITIES

12. AUTONOMIC FEATURES

13. MOTOR ABNORMALITIES

14. Ictal examination for Semiology

15. Ictal and postictal clinical feature with localization

16. Imaging CT
• Sturge weber syndrome – Tram track calcification.
• Calcification associated with neurocysticercosis.
• Tuberous sclerosis sub ependymal tubers.
• Abandoned in most epilepsy centers.
• 95 % Vs 32 % sensitivity (MRI Vs CT).
• Probability of positive CT in negative MR 0 %
while 80 % positive MR in CT negative cases.

17. Imaging MRI
• The primary role- to locate and define structural lesions.
• In TLE sensitivity is 75 % to 100 % for hippocampal sclerosis, Specificity 70- 85 %
• MRI also can depict relation of epileptogenic foci and functional tissue.
• Classic findings (MTS)-as a result of gliosis and the subsequent increase in free
water content.
• Associated findings -atrophy of the ipsilateral mammillary body, fornix, and other
parts of the limbic system

18. Imaging MRI
• Thin-section volumetric T1W imaging-used to calculate hippocampal volume
(Does not depict abnormal signal intensity, less useful than FLAIR and T2W for visual detection of MTS)
• T2W imaging is better than FLAIR for demonstrating the internal architecture of the hippocampus
• Coronal oblique MRI through the temporal lobes perpendicular to the plane of the hippocampus is the
(preferred modality)
• A FLAIR- nulls the CSF signal, Degree of signal abnormality is more obvious in hippocampus
• A pitfall of coronal FLAIR image- slight hyperintensity of all limbic structures relative to the neocortex.

19. T1 coronal images. Left hippocampal sclerosis is associated with widening of temporal horn and ipsilateral atrophy of fornix (A) and mammillary body (B) (arrows).
T1W Coronal

20. A and B, Axial and coronal images, showing migration and sulcation disorders, with gray matter nodular heterotopy. Note
the abnormal localization of gray matter in deep white matter lateral to right ventricle with ependymal extension (arrows).
T2W Axial & Coronal

21. A, T2 coronal image with region of interest measurement of the hippocampus. There is atrophy and hyperintensity on the left due to hippocampal sclerosis (arrow).
B, Flair sequence of coronal image showing left hippocampal hyperintensity (arrow), corresponding to sclerosis and atrophy.
T2W FLAIR
• When structural MR imaging does not demonstrate a lesion
• Volumetric neocortical measurements may provide an objective way
to evaluate the extent of resection and its relation to surgical results
Quantitative MR imaging

22. Diffusion Tensor Imaging
• In the white matter, diffusion
greatest parallel to the white matter tracts
minimal perpendicular to them.
• Malformations of cortical development and acquired lesions.
Increased mean diffusivity.
Increased perpendicular diffusivities.
Tractography of horizontal temporal-frontal and temporal-occipital (Meyer’s) tracts,
there is interruption of fibers of Meyer’s loop (arrow).

23. Magnetic Resonance Spectroscopy(MRS)
• MRS is a powerful adjunct to MR imaging.
• Consistent with the HPE characteristics of
reduced neuron cell counts or neuronal
dysfunction and increased glial cell numbers
• Reduced NAA and increased Cho in TLE.
• Extratemporal lobe epilepsy, the ability of MR
spectroscopy to lateralize the epilepsy is less
(50%).
Hippocampal univoxel spectroscopy. There is bilateral reduction of N-acetyl-aspartate
compatible with hippocampal sclerosis

24. Functional MR Imaging
• Used for mapping language, memory, and
sensorimotor location for presurgical planning.
• This imaging modality is based on
- the observation that increased neuronal activity
-a/w an increase in CBF
-therefore an increase in the
oxyhemoglobin/ deoxyhemoglobin ratio.
fMRI study showing left cerebral hemispheric dominance for language in a healthy subject using a phonologic
category

25. EEG (Electroencephalography)
• The inventor of EEG in 1924 Hans Berger German psychiatrist.
(alpha wave /"Berger wave.")
Used for recording the electrical activity of the brain,
• Awake & Sleep
• Ictal & Interictal
• Eye opening & Closure, Hyperventilation, Photic stimulation.
• Surface/ video/ Invasive / Combinations
• Lateralization (left vs. right hemisphere) and localization
• The presence of interictal (between seizures) epileptiform discharges. EDs:
sharp waves or spikes.
• Lack of EDs does NOT rule out epilepsy (up to 10%).
• Spike waves : negative transients with steep ascending and descending
limbs and a duration of 20 to 70 ms.

26. Scalp EEG
• Interictal s/o increased epileptogenic potential.
• Ictal Eds s/o classification of seizure, brain
region of seizure activity.
• Sensitivity and specificity depends upon,
Localization of epileptic brain tissue.
Duration of recording.
Use of supplementary electrodes.
Frequency of seizures
Timing in relation to last seizure.
(A) EEG showing left temporal interictal epileptiform discharges;
(B) 7-Hz-rhythmic theta activity over the left temporal region;
(C) left hippocampal atrophy and increased signal on T2W MRI sequence
(D) postoperative MRI showing complete resection of lt ant temporal
lobectomy with AHC.

27. Human EEG with prominent resting state activity – alpha-rhythm. Left: EEG traces (horizontal – time in seconds; vertical – amplitudes, scale 100 μV). Right: power spectra of shown signals (vertical lines – 10 and 20 Hz,
scale is linear). Alpha-rhythm consists of sinusoidal-like waves with frequencies in 8–12 Hz range (11 Hz in this case) more prominent in posterior sites. Alpha range is red at power spectrum graph.
Human EEG with prominent resting state activity
Common artifacts in human EEG. 1: Electrooculographic artifact caused by the excitation of eyeball's muscles (related to blinking, for example). Big-amplitude, slow, positive wave prominent in frontal electrodes. 2: Electrode's artifact caused by
bad contact (and thus bigger impedance) between P3 electrode and skin. 3: Swallowing artifact. 4: Common reference electrode's artifact caused by bad contact between reference electrode and skin. Huge wave similar in all channels.
Common artifacts in human EEG

28. EEG recording for temporal lobe area
Medial temporal lobe epilepsy usually have EDs from the anterior-mid temporal lobe
(electrodes F7/F8, T3/T4, as well as anterior temporal, sphenoidal, and inferior temporal electrodes if used).

29. Background EEG that showed mild independent bilateral temporal and generalized slowing;
(b) right anterior temporal spikes (∗); (c) left anterior temporal spikes (∗∗)
(right temporal IEDs to left temporal IEDs 70 : 30) in sleep; (d) left temporal type 2 ictal rhythm as rhythmic delta activity in the left temporal
regions (arrows) during one of her typical complex partial seizures (seizure onset zone).

30. Video EEG
• The combined use of video and EEG recording improves the
sensitivity and specificity over EEG recording alone.
• In many cases -as a first study in the proper classification of
the seizure disorder.
• A typical duration of inpatient monitoring is 3 to 5 days.

31. Video EEG
• Video-EEG monitoring has been demonstrated to-
 to accurately differentiate between epileptic and non-epileptic seizures
 to distinguish between primarily generalized and partial onset seizures,
 to determine seizure onset localization and lateralization
Stereo-EEG (SEEG)- is the surgical implantation of
electrodes into the brain in order to better localize the
seizure focus.

32. Magnetoencephalography (MEG)
• First MEG recording(1968) performed by Dr. Cohen using a single
channel, (more than 300 sensors)
• The MEG modality measures extracranial magnetic fields perpendicular
to the direction of intracellular currents in apical dendrites.
• Able to measure the epilepsy specific information (i.e., the brain activity
reflecting seizures and/or interictal epileptiform discharges) directly
• Non-invasively and with a very high temporal resolution (millisecond-
range).
• Advantages of MEG as opposed to EEG studies
-magnetic fields are minimally affected by conductivities of
intervening structures
-tissues between brain and scalp.
-superior than EEG in localizing the irritative zone
(Frontal, intrasylvian or insular focus )
Figure 1: MEG acquisition: (a) MEG (306 channel) dewar inside
a magnetically shielded room (MSR), (b) Five-head positioning
indicator (HPI) coils for head movement monitoring during
acquisition, (c) 3D-digitization carried out using a wooden chair,
goggles with transmitter, and a stylus with receiver, (d) patient
MEG data acquisition with simultaneous EEG in erect posture

33. MEG

34. Invasive EEG monitoring
INDICATIONS:
• Seizures are lateralized but not localized.
• Seizures are localized but not lateralized.
• Seizures are neither localized nor lateralized (eg, stereotyped complex partial seizures with diffuse ictal changes).
• Seizure localization is discordant with other data.
• Relationship of seizure onset to lesion must be determined (eg, dual pathology or multiple intracranial lesions).

35. Invasive EEG monitoring
• Temporal lobe seizures
• -Doubtful side
• -Normal MRI
• -Bilateral pathology
• - Discordant non-invasive testing
• Extratemporal seizures
• -Definition of extent of epileptogenic area
• -Extra-operative cortical mapping
 Depth,
 strip
 grid electrodes
• Implantable intracranial devices used to record the
electrocorticogram (ECoG).
• to stimulate the cortex to determine function.
• Depth electrodes are multicontact, thin, tubular, rigid or
semirigid electrodes.
• Penetrate the brain substances for the purpose of recording
from deep structures.

36. TYPES OF ELECTRODES
• Intracranial strip electrodes are a linear array of 2-16 disk electrodes
embedded in a strip of silastic or in tubular in structure
• Grid electrodes are parallel rows of similar numbers of electrodes that
can be configured in standard or custom designs.
• Grid and strip electrodes are designed to be in direct contact with
brain neocortex.
• Electrodes are placed in the subdural space/ the epidural space.

37. TYPES OF ELECTRODES
• Constructed from biologically inert materials (ie silastic, stainless
steel, platinum).
• Platinum electrodes are more easily seen on fluoroscopic images
and are compatible with MRI.
• The morbidity of surgery depends on the type of electrode
 intracranial strip electrodes-lowest morbidity.
Intracranial grid placement-highest morbidity.
• Transient neurological deficit, hematoma, cerebral edema with
increased intracranial pressure, and infarction.

38. Wada test
• Developed by Dr Jun Wada. AKA intracarotid sodium amobarbital procedure (ISAP)
• Neuroradiologist, Epileptologist, Neuropsychologist
• To preoperatively determine which hemisphere contains language function
• To test memory function within each hemisphere
Procedure:
• Accomplished by individually cannulating each internal carotid artery.
• After contrast arteriography verifies that blood flows to the corresponding hemisphere
and not to the brainstem or contralateral side,
• A dose of sodium amobarbital (sufficient to impede hemispheric function) is injected.
• Both sides of the brain are tested in one day. Usually, there is a wait of 30 to 60 minutes
before the second side is tested, Test is done as an outpatient test

39. Wada test
• Different word, object, and picture cards are shown, and the awake side tries to recognize and remember what it sees.
• If speech persists in the face of this hemiparesis, language function is assumed to not be represented within that
hemisphere.
• The deficiencies of this evaluation for memory function directly relate to the multiple problems.
Injection of a drug into the ICA does not assure drug effect in the basal
temporal area in general or the hippocampal region specifically.
(due to variations in the direct blood supply to the hippocampus)
• Complication like pain haemorrhage, infection
• Alternate possible test- fMRI

40. Recent Advances- Nuclear imaging
Positron emission tomography (PET)
• An injection of radio-labeled glucose (18FDG) to measure brain metabolism.
• Interictal PET -shows hypometabolism in the seizure focus, especially in TLE.
• Ictal PET is not practical due to the extremely short half life of the radiotracers used.
• PET is most useful in MRI-negative TLE, (non-lesional, extra-temporal epilepsy)
• FDG PET identifies sites of interictal metabolism in 70 % with TLE and 60 % frontal
lobe onset seizure.
• C -11 flumazenil PET effective in hippocampal sclerosis & shows pathological foci in a
more circumscribed fashion.
In 80% of patients there is an increase in blood
flow and glucose metabolism during a seizure in
the cerebral cortex. However, between seizure
there tends to be a lower than normal glucose
uptake and blood flow.

41. Single photon emission computed tomography(SPECT)
• Ictal SPECT ideal method for localization and lateralization of
seizure onset, Shows hypermetabolism
• SPECT also performed better in the setting of negative MRI.
 Inter ictal scan – Hypoperfusion large area in the hemisphere of
onset.
 Ictal /Interictal quantitative difference analysis provides for the
best and most reliable seizure focus localization

42. Subtraction ictal- interictal SPECT co-registered to MRI (SISCOM):
• A newer methodology that has greater accuracy than either ictal or
interictal SPECT scanning.
• This requires obtaining scans separated by at least 48 hrs to
accommodate radionucleotide wash out during an interictal period and
within seconds of seizure onset.
• These scans are then subtracted from one another with the use of
specialized computer software.
• This leaves a better indication of the cortical area of ictal onset.
• This subtracted scan can then be co-registered onto the patient's MRI to
provide support for the location of the focus.

44. Conclusion
• Epilepsy semiology-an improved understanding of epilepsy related issues and localizations
• MRI is most sensitive for identification of a structural lesion.
• A routine EEG- correlate cerebral dysfunction and a potential epileptogenic zone.(EZ)
• Ictal video-EEG -mirror foci, false localization & lateralization, secondary epileptogenesis
• Invasive video-EEG with extra-operative epidural, subdural, or depth electrodes-needed to define complex EZ
• The Wada test -determine lateralization of language and memory; fMRI is possible alternative
• SPECT and PET scans- confirm a functional relationship between radiologic lesion and EZ

45. Role of Patient management conference
• Epilepsy Patient Management Conference (EMC) - multidisciplinary weekly meeting
• Single most important discussion forum for the management of complex patients
• Epilepsy team – neurologist, surgeons, advanced practice nurses, administrators and
coordinators, neuropsychologists and neuroradiologists
• To discuss and synthesize the data gathered for particular patients who have undergone
Phase I monitoring.
• Discussion concludes with a formulation of a consensus management plan for the pt.
whether the patient would benefit from epilepsy surgery.
If so, further tests are usually necessary to confirm surgical candidacy.
and on the completion of those ancillary tests, the data are re-discussed
• In this iterative fashion a final management plan is made which is then communicated
to the patient by the team

46. Thank you