TREATMENT OF EPILEPSY
N. Eskandar, M.D.
Patient Appointments: 617.724.6590
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In the majority of patients with
epilepsy, seizures can be well controlled with appropriate medication.
However, current estimates indicate that 20 - 30% of patients
with epilepsy are refractory to all forms of medical therapy.(1)
These medically intractable patients are candidates for surgical
treatment in an attempt to achieve better seizure control. Another
group of patients who might benefit are those whose seizures may
be relatively well controlled but who have certain characteristic
presentations or lesions that strongly suggest surgical intervention
might be curative. Overall, the single most important determinant
of a successful surgical outcome is patient selection. This requires
detailed presurgical evaluation to characterize seizure type,
frequency, site of onset, psychosocial functioning and degree
of disability in order to select the most appropriate treatment
from a variety of surgical options. This type of evaluation is
best carried out at a multi-disciplinary center experienced in
the investigation and treatment of epilepsy.
In this article, we will outline
the essential elements of the presurgical evaluation as well as
the diagnostic surgical procedures required for invasive EEG monitoring
and then describe the variety of therapeutic surgical options
including indications, techniques, results and complications of
There are many types of seizures
and different forms of epilepsy. A seizure is defined as a paroxysmal,
self-limited change in behaviour associated with excessive electrical
discharge from the central nervous system. Epilepsy is defined
as a condition of recurrent seizures and medical intractability
as recurrent seizures despite optimal treatment under the direction
of an experienced neurologist over a two to three year period.
In the past, seizures have been
classified based upon their clinical manifestations which had
some relevance for patients and physicians but was of limited
diagnostic or prognostic value. This classification scheme is
based entirely on the distinct behavioural and electrophysiologic
features of the seizures themselves and purposely avoids implications
as to the specific underlying pathophysiological mechanisms or
substrates.(2) According to this classification, an epileptic
disorder is defined as either being generalized, partial (focal)
or undetermined. Primary generalized seizures start as a disturbance
in both hemispheres synchronously without evidence of a localized
onset. The manifestations of these seizures tend to be major motor
seizures of a tonic, clonic, tonic-clonic, myoclonic or atonic
type. They also include minor events of the petit mal (absence)
type. Partial forms of epilepsy start in a focal area of the brain
and may remain localized without alteration of consciousness.
These events are referred to as simple partial seizures and the
symptoms vary with the area of the brain affected. If the event
spreads and alters consciousness it is referred to as a complex
partial seizure. If the event spreads further and leads to a major
motor seizure it is referred to as a secondarily generalized seizure
and may be quite difficult to distinguish from the primary generalized
forms. Partial seizures often arise from the limbic structures
of the temporal and frontal lobes but can occur from any cortical
region and are often quite refractory to medical therapy alone.
In general , patients with partial seizure disorders are the most
amenable to surgical intervention.
A second classification divides
the clinical epilepsies into idiopathic, symptomatic and syndromic
forms based upon their presumed etiologies.(3) Idiopathic forms
include some of the generalized seizure types that may have familial
patterns but without a prominent genetic component such as simple
febrile convulsions of childhood. Symptomatic forms are those
caused by a recognized central nervous system (CNS) lesion. Included
in this type are cases of known structural pathology, metabolic
abnormalities or neurodegenerative processes. Syndromic forms
include disorders that may be idiopathic or symptomatic but seem
to follow a clear and predictable course. These include childhood
and juvenile absence epilepsies, juvenile myoclonic epilepsy and
the Lennox-Gastaut Syndrome. The ability to place a patient in
one or another of the syndromic categories has the advantage of
providing a basis for predicting long term prognosis.
Both classifications have certain
advantages and are not mutually exclusive but can be combined
to provide helpful information. From a surgical point of view
however, dividing the seizure types into either generalized or
focal appears to be the most useful. This is because most surgical
decisions are based upon defining those seizures that originate
in one focal area of the brain and localizing that area as a prelude
The goal of epilepsy surgery is
to identify an abnormal area of cortex from which the seizures
originate and remove it without causing any significant functional
impairment. The primary components of the presurgical evaluation
includes a detailed clinical history and physical examination,
advanced neuro-imaging, video-EEG monitoring, neuropsychological
testing and assessment of psychosocial functioning. (Table 1)
The major surgical questions one hopes to answer with this evaluation
are: 1) are the seizures focal or generalized ?; 2) if focal,
are they temporal or extratemporal in origin ?; 3) is there a
lesion associated with the seizures ?; and 4) if surgery is undertaken
what functional deficits, if any, might be anticipated?
The presurgical evaluation of a
patient with medically intractable epilepsy begins with a complete
history and physical examination. One attempts to classify the
different kinds of seizures as well as the frequency, severity
and duration of each type. The clinical semiology of these events
can yield important localizing information to the experienced
clinician. It is also important to determine the age of onset,
response to treatment and familial tendency to seizures. The pregnancy
and delivery history is helpful in assessing congenital or early
acquired abnormalities. Other past medical history of significance
would include a history of febrile seizures, head injury or intracranial
infection. An assessment of the adequacy of medication trials
must also be made to ensure that the patient is truly refractory
to medical therapy.
On examination, the clinician looks
for obvious asymmetries of development compatible with an early
structural CNS lesion and focal neurologic or cognitive abnormalities
suggestive of acquired disease. In the great majority of patients,
however, the neurological examination is completely normal.
Electroencephalographic (EEG) Investigation
Modern neuroimaging is crucial to
surgical decision making. In the past, skull x-rays, ventriculograms,
pneumoencephalography and computerized tomography (CT) scans demonstrated
indirect evidence of cerebral pathology in the form of focal or
diffuse atrophy or space-occupying lesions. Recently, magnetic
resonance imaging (MRI) has replaced CT scanning as the imaging
study of choice to evaluate patients with epilepsy. MRI is an
extremely sensitive tool that can detect abnormalities of the
brain with exceptional anatomical detail. (figure 1) This has
been especially true for detecting focal atrophy ( e.g. hippocampal
atrophy ), indolent gliomas, cortical dysplasias, cerebral gliosis
and small structural lesions of the neocortex.(4) Functional imaging
attempts to visualize alterations in cerebral metabolism using
Positron Emission Tomography (PET) and Single Photon Emission
Computerized Tomography (SPECT). These studies reveal epileptic
areas as hypometabolic between seizures and hypermetabolic during
seizures.(5,6) (figure 2) Although they lack the spatial resolution
of MRI, PET and SPECT can play an important role in the localization
of abnormal cortex. Ictal SPECT studies can be obtained if injection
of an appropriate radioisotope is performed within seconds of
a seizure onset. The isotope is concentrated in the region of
seizure onset and imaging studies can be obtained up to several
hours after injection to demonstrate the area of ictal onset.
These studies have been useful in many patients with occult epileptic
Electroencephalographic (EEG) investigation
remains the most important aspect of the presurgical evaluation.
Analysis of unselected EEG activity between events (interictal
) or of specific activity during events (ictal ) can provide evidence
of focal electrical dysfunction. While certain interictal EEG
abnormalities (spike and slow wave complexes) can be of localizing
value, it is considered extremely important to record the EEG
with concommitant videotape during the spontaneous occurrence
of the patient's events. Video/EEG monitoring can continuously
record the EEG over a 24 hour period which allows for careful
inspection of the record during any symptomatic event. Sophisticated
computer hardware and software also allows for automatic detection
of spontaneous interictal epileptiform transients and electrographic
seizures that otherwise might have gone unrecognized.(8) It is
the EEG activity at the very beginning of the seizure before spread
to adjacent areas that is most important in terms of localization
and if a specific cortical area is involved consistently at the
onset then that area is likely to be the site of seizure origin.
Patients are often hospitalized with reduction in anti-seizure
medications and may be recorded for up to 7-14 days in order to
capture 3-5 of their habitual seizures.
Detailed neuropsychological testing
is carried out to reveal specific focal or multifocal cognitive
deficits that might be correlated with the neuroimaging and EEG.
This testing may help in localizing an abnormal area of the brain
but also serves as a comparison for post-surgical evaluation.
An intracarotid amobarbital test is generally done as a prelude
to surgery in order to lateralize language and memory function
and to avoid neurocognitive deficits.(9)
DIAGNOSTIC SURGICAL OPTIONS
Psychosocial evaluation is also
extremely important to assess current level of functioning and
to ensure realistic goals and attitudes are engendered in both
the patient and their family prior to surgery.
When a primary epileptogenic region
or seizure focus is suspected but remains obscure despite appropriate
neuro-imaging and scalp (non-invasive ) video/EEG recordings,
some form of implanted (invasive ) electrodes may be indicated.
Intracranial electrodes can be placed in areas not readily sampled
by routine surface electrodes and can give more precise EEG information
because of their proximity to discharging areas of the brain and
the lack of movement/muscle artifact on the recordings. They have
the disadvantage, however, of sampling from a relatively small
area of cerebrum surrounding the contact points and the fact that
they are accompanied by a surgical risk. They should only be undertaken
after appropriate noninvasive monitoring has been completed so
that an hypothesis of seizure onset has been formulated and a
clear goal of the investigation has been defined. The diagnostic
surgical options of implanted electrodes include epidural, subdural
and intracerebral or depth electrodes.
Epidural electrodes are used infrequently
and generally only for lateralization and approximate localization
of seizure onset.(10) These electrodes are placed through tiny
openings in the skull with the electrode contact resting on the
dura to provide a high amplitude EEG signal without muscle or
movement artifact. Because they do not penetrate the dura the
risk of infection is minor. These electrodes can only record from
the lateral convexity of the cerebral hemispheres and therefore
are limited in their spatial resolution.
Intracerebral depth electrodes
These electrodes are placed subdurally
on the surface of the brain in the form of rectangular grids or
linear strips with flat metal contact points mounted in flexible
plastic. The grids require a craniotomy for placement and therefore
are limited to unilateral application. (figure 3) The strip electrodes
can be placed through burr holes over the lateral convexity or
under the frontal or temporal lobes.(11) It is difficult to place
them in the interhemispheric fissure to record from parasaggital
regions because of technical risks associated with large cortical
veins. The major advantage of subdural electrodes is that they
do not penetrate cerebral tissue and can record from a relatively
wide area of the cortical surface. They can also be used for extraoperative
cortical stimulation to map out specific areas of cortical function.
Unfortunately, subdural electrodes cannot record directly from
the deep cerebral structures (i.e. amygdala, hippocampus and cingulum)
which are characteristically involved in many medically refractory
partial epilepsies. They also have a small but real risk of intracranial
infection and hemorrhage estimated to be approximately 4%.(12)
SURGICAL DECISION MAKING
Intracerebral depth electrodes can
be placed stereotactically into deep cerebral structures with
the aid of CT, MR and angiography. Most centers employ flexible
electrodes with multiple contact points that are placed through
small holes in the skull and secured with some form of cranial
fixation. (figure 4) Electrodes are usually targeted towards the
amygdala, hippocampus, orbital-frontal and cingulate regions and
may be inserted via a lateral or vertex approach. Using a lateral
approach, stereotactic cerebral angiography must be utilized to
avoid major blood vessels during placement of the depth electrodes.
Depth electrodes may be used in combination with scalp or subdural
electrodes for more extensive coverage. Depth electrode investigation
is generally indicated for patients with bitemporal, bifrontal
of frontal temporal seizures and can localize a focal area of
seizure onset not possible with scalp recordings.(13) The major
complications of depth electrodes include hemorrhage and infection
with mortality and morbidity rates between 1 - 4%.(12) It should
be noted that the intracranial monitoring incurs greater risk
than resective surgery itself and is also considerably more expensive
than a noninvasive evaluation and therefore should be used only
when necessary. With modern neuro-imaging, the use of invasive
intracranial monitoring has declined from about 40-50% of patients
in most centers to 10-20%.
THERAPEUTIC SURGICAL OPTIONS
If the information obtained during
the noninvasive presurgical evaluation consistently points towards
a single area of the brain as being the site of seizure onset,
then the patient may be taken directly to surgery for resection
of that area. If neuro-imaging demonstrates a well-characterized
lesion ( i.e. unilateral hippocampal atrophy, cavernous angioma,
focal cortical dysplasia, etc.) and is supported by the clinical
features of the seizures then surgery may be reasonable without
the general requirement for ictal EEG data.. However, if the data
gathered from the clinical examination, imaging studies and noninvasive
EEG evaluation are conflicting or disparities arise in the presumed
localization of the seizure, then invasive intracranial monitoring
is warranted. This is especially true in the extra-temporal epilepsies
where EEG localization is notoriously difficult. If a localized
area of seizure onset is confirmed then these patients too can
undergo resective surgery.
Epilepsy surgery began as removal
of gross structural lesions of the brain. With the addition of
EEG data from preoperative and intraoperative recordings, areas
of removal expanded to include tissue that was grossly normal
in appearance but known to give rise to epileptiform activity.
Small areas of resection were soon replaced by partial lobectomies
and more extensive cortical resection. While resection techniques
( lesionectomy, lobectomy, hemispherectomy, corticectomy) generally
yield the best surgical results, disconnection (callosotomy, subpial
transection) and augmentation (cerebellar and vagal stimulation)
techniques remain worthwhile considerations (Table 2).
The primary objective of most epilepsy
surgical procedures is to accurately localize and then completely
excise the epileptogenic region without causing cognitive or neurologic
deficit. An important determinant of the risk of surgery is the
relationship of the lesion to functionally important or "eloquent"
brain regions because injury to these "eloquent" areas can cause
irreversible neurologic impairment. The location of many functionally
important areas can be approximated using anatomic landmarks but
individual variations occur and the presence of local pathology
can distort landmarks making localization imprecise. Regions responsible
for seizure onset must be distinguished from regions of critical
cortical function and a variety of strategies have therefore been
employed both pre- and intra-operatively to optimize surgical
resection while minimizing risk of injury to functional cortex.
Some centers utilize intraoperative
cortical recordings to sample EEG activity from the cerebral surface
and to allow for cortical mapping. Classical cortical mapping
requires a craniotomy under local or light general anaesthesia
and direct electrical stimulation of the cortex using a hand-held
stimulator.(14) This allows for precise individual localization
of sensory, motor and language areas but unfortunately, the information
cannot be used preoperatively for risk assessment, therapeutic
decision-making and surgical planning. Centers that use subdural
grid electrodes may carry out functional mapping extraoperatively,
in advance of the cortical excision, by passing small currents
between implanted electrodes.(15) This lacks the spatial precision
of intraoperative stimulation but can be very useful especially
in children or uncooperative adults. Localization of the rolandic
sulcus may also be carried out by recording somatosensory evoked
potentials and the recognition of their phase reversal over the
The newest method of localizing
cortical function is with functional MRI. This powerful neuroimaging
technique can create an anatomical and functional model of an
individual patient's brain. Rapid echoplanar imaging performed
while the patient engages in a specific task ( i.e. fist clenching,
tongue movement, verb generation) detects small changes in signal
intensity related to changes in cerebral blood flow.(17) Intensive
computerized image processing can then define the areas of cortex
activated by the specific task. Concurrent 3-dimensional rendering
of cerebral topography, cortical veins and related pathology gives
an unprecedented display of critical relational anatomy. By combining
detailed anatomical information with precise physiological information,
fMRI is capable of creating a structural and functional model
of an individual's brain. (figure 5) It is likely that fMRI will
play an increasing role in the presurgical evaluation of epilepsy
Other non invasive cerebral mapping
techniques that have evolved to localize functionally important
cortical areas are magneto-encephalography (MEG) and positron
emission tomography (PET). Both can localize certain cortical
functions non-invasively but require dedicated units that are
not widely available.
After the resection strategy is
decided upon, tissue removal is carried out using subpial resection
techniques. Cortical gray and white matter is carefully removed
by suction or cavitron so that the pia remains intact over the
adjacent gyri. This tends to form a nonscarring barrier and preserves
blood supply to the remaining cortex as well. Following removal,
some centers carry out post-resection cortical EEG recordings
and may carry out further removal if considerable epileptic activity
remains at the resection margins.
With the advent of MRI, many patients
with recurrent seizures are now discovered to have small, previously
unrecognized lesions such as cavernous angiomas, low grade astrocytomas,
cortical dysplasias and areas of focal atrophy that are clearly
the cause of their seizures. In general, if these are located
in extratemporal sites, removal of the lesion and a small rim
of surrounding cortex is often successful in controlling seizures.
Removal of significant perilesional cortex may be necessary to
achieve optimal seizure control in some patients. In many instances,
if only a portion of the lesion is removed, the surgical result
is suboptimal. If lesions are located within the temporal lobe,
lesionectomy along with temporal lobectomy is carried out including
the mesial temporal structures in order to yield good results
in 80% of cases.(18) Overall, lesionectomy is associated with
excellent results with success rates that are generally better
than with surgery performed in patients without discrete lesions.
The majority of resections involve
the temporal lobe and initially consisted of the classical anterior
temporal lobectomy. This was either carried out "en-bloc" under
general anesthesia or using a more tailored resection with electrocorticography
and cortical mapping under local anesthesia. The majority of temporal
lobectomies, whether in the dominant or nondominant hemisphere,
can now be safely performed under general anesthesia with or without
electrocorticography. In the dominant hemisphere, temporal lobe
removals usually extend back 4.5 - 5 cm. behind the temporal tip
or to the level of the central sulcus. In the non-dominant hemisphere,
temporal lobectomies can extend beyond 7 or 8 cm but will result
in a contralateral superior quadrantanopsia because of encroachment
upon the optic radiation. It is important that the mesial temporal
structures are included in the removal because most neurosurgeons
believe that the hippocampus is intimately involved in seizure
propagation or amplification. Studies also indicate that recurrent
seizures are more likely following temporal lobectomy when the
hippocampus is not removed.(19)
Since almost 80% of temporal lobe
seizures originate in the mesial structures, several operative
approaches have been designed to reduce the amount of temporal
neocortex removed but still resect the amygdala and hippocampus.
The so-called antero-medial temporal lobectomy with amygdalo-hippocampectomy
is a modification of the classical temporal lobectomy by reducing
the amount of cortical removal and extending the hippocampal resection.(20)
(figure 6) Selective amgdalo-hippocampectomy removes the mesial
temporal structures via either trans-sylvian, transcortical or
trans-sulcal microsurgical approach with the goal of sparing temporal
neocortex and reducing any possible neuropsychological deficits.(21)
(figure 7) Some cortical injury and white matter disruption does
occur with this technique and it is only applicable to patients
with clear cut mesiobasal temporal lobe epilepsy. No matter which
procedure is advocated, if patient selection is appropriate, surgery
in the temporal lobe offers good to excellent results in 75 -
85% of the cases. With modern imaging techniques, seizure free
rates are now approaching 90% with febrile seizures, hippocampal
atrophy and mesial temporal sclerosis being positive predictors
of a good outcome.
Morbidity and mortality figures
for cortical excisions are quite low, less than 0.2% in one large
series with over 2000 patients.(22) The incidence of hemiparesis
was 0% following temporal lobectomies and 0.5% for hemiparesis
and/or dysphasia following frontal lobectomies.(23) In dominant
hemisphere removals, however, there is often a temporary speech
deficit. Specific cognitive testing may detect permanent subtle
deficits consistent with the site of removal but generally these
are nonspecific.(24) An upper quadrantanopsia may occur with larger
temporal removals in the nondominant hemisphere. This may be acceptable
if required for seizure control since it is usually unnoticed
by the patient and does not interfere with normal daily living.
Memory impairment has occurred with unilateral temporal removals
in rare cases but this complication is avoided by preoperative
testing of speech and memory function during the intracarotid
amytal test. If memory is affected by amytal injection ipsilateral
to the proposed side of the temporal removal, temporal excision
may be designed to spare the hippocampus and medial structures
but this approaach may reduce operative success rates.
Extra-temporal resections are much
less commonly performed with the majority being carried out in
the frontal lobe. En bloc standardized resections are not generally
suitable and most surgeons guide their resections by detailed
electrocorticography, both intra- and extra-operatively along
with detailed cortical mapping. Frontal resections range from
localized topectomies to complete frontal lobectomies and must
be carefully individualized. Identification of the primary motor
cortex is essential to avoid motor deficits and anterior language
cortex to avoid speech difficulties. Parietal and occipital resections
are rarely carried out but may be gratifying in patients with
clear structural lesions.
The results of cortical excision
for extratemporal epilepsy are variable depending upon patient
selection and method of presurgical evaluation. Outcome statistics
are not as impressive for extra- temporal resections as they are
for temporal removals. Nevertheless, extra-temporal resections
including the frontoparietal and occipital regions can give excellent
results. Patients with epileptic discharge limited to the lobe
of resection obviously tend to do better than those with more
widespread discharges. In addition, some patients have more wide
spread epileptogenic zones that require multilobar resections.
In the largest cumulative series 64% of patients were improved,
36% being seizure free.(23) With advances in neuro-imaging and
other aspects of the presurgical evaluation, it is hoped that
surgical success rates can improve in the future.
Hemispherectomy is another form
of cortical excision that is limited to patients with congenital
hemiplegia, chronic encephalitis, hemi-megalencephaly or Sturge-Weber
syndrome. These patients tend to have severe epilepsy with wide
spread independent epileptic discharges that often extend to the
contralateral (normal) hemisphere. It is only performed on patients
who have a dense hemianopsia and are already hemiplegic with no
fine motor activity on the affected side. The acute surgical risk
is that some crude movement or sensation on the opposite side
of the body would be adversely affected. A chronic complication
was recognized to occur approximately 8 to 10 years after gross
total hemispherectomy. This condition called superficial cerebral
hemosiderosis resulted from chronic leaking of blood into the
resection cavity producing recurrent seizures, sensori-neural
deafness and hydrocephalus. It occurred in approximately 25% of
patients by ten years and mandated a modification of the procedure.(25)
This complication is now avoided by performing a anatomically
subtotal but functionally complete hemispherectomy in which the
frontal and occipital poles are left in place with their blood
supply but all neural connections are transected. Residual cerebral
tissue either decreases the risk of hemorrhage into the resection
cavity or alternatively absorbs any blood that might leak in.
Alternatives to anatomical hemispherectomy include hemispherotomy,
cerebral hemicorticectomy, dural plication and ventriculoperitoneal
shunting. All of these modifications attempt to reduce the risk
of superficial cerebral hemosiderosis by minimizing cortical resection
while maintaining complete functional disconnection.
Functional hemispherectomy or any
of its variants, is one of the most successful surgical procedures
for epilepsy with over 85% markedly improved and about 60% seizure
free.(25) Many patients also demonstrate behavioral improvement
probably on the basis of a better attention span and cognitive
Multiple Subpial Transections
Corpus callosotomy has been offered
as an alternative to hemispherectomy in epileptic patients with
congenital hemiplegia but the results are not as good as with
hemispherectomy. It is indicated when the patient has a severely
damaged hemisphere but motor, sensory or visual function that
would be valuable to preserve. In general, however, corpus callosotomy
ismost useful for those patients with generalized seizure disorders
and bilateral independent epileptic areas in the frontal region.
The seizures that respond best to callosotomy are sudden falls
or "drop attacks" with injury to the patient. Some patients with
additional focal seizures may experience an improvement or overall
reduction in these partial seizures but about 20% of patients
will have an increase in the number of focal seizures. The generalized
seizures and drop attacks tend to improve markedly although a
complete cure of seizures is extremely rare.(26) Early surgical
experience included deaths and severe morbidity but the risks
have become extremely low with modern microsurgical techniques.
The current practice is to section the anterior 2/3 of the corpus
callosum on the first procedure. The posterior 1/3 may be sectioned
at a second procedure if the results of anterior section are not
satisfactory. Transient abulia is common following anterior callosotomy
but other disconnection effects are fortunately mild and uncommon.
In patients with complete callosotomy, disconnection symptoms
are more frequent. There is often some difficulty in bimanual
tasks and apraxia for commands directed to the nondominant extremity.
Visual presentation to the hemifield opposite to the dominant
hemisphere cannot be comprehended or described by language modalities
and there is often significant difficulty writing with a nondominant
hand. Fortunately, most of these functional deficits are not noticeable
in normal daily living and are balanced by the improved seizure
In patients with seizure onset or
epileptic zones located in eloquent cortex, multiple vertical
subpial transections have been recommended as an alternative to
cortical resection. This technique leaves the vertical columnar
arrangement of the cortex intact thereby preserving function but
prevents spreading of the seizure discharge in the horizontal
plane to reduce seizures. Some neurological deficits appear postoperatively
but these generally resolve over several weeks with satisfactory
improvement in seizure control in 70 % of patients.(27) Experience
with this technique is still rather limited but it does provide
a surgical option in patients with seizures arising in cortex
that has been previously considered inoperable.
Stereotactic lesions of deep cerebral
structures have been carried out for a variety of generalized
and focal forms of epilepsy in the past. Bilateral cingulotomies,
amygdalotomies, lesions in the Field of Forel and thalamic lesions
have all been tried.(28) Results are scattered and too few for
any conclusions to be made although generally they are unimpressive.
While some lesions may have an initial good result, seizures tend
to recur in virtually all patients and stereotactic ablations
of subcortical structures are no longer in use.
Vagus nerve stimulation
Cerebellar electrical stimulation
has been used to treat generalized focal and myoclonic seizures
as well as for spasticity of cerebral palsy.(29) Cerebellar stimulation
has a theoretical basis from animal studies in which lesion induced
cortical discharges were reduced or inhibited by cerebellar electrical
stimulation. Initial reports of clinical success could not be
reproduced. Reports followed of tissue damage from the cerebellar
stimulator and a large number of late failures. Improvement in
the technical quality of the electrodes and stimulating devices
has led to some renewed interest in this technique but it is not
currently a recommended treatment and no definitive evidence supporting
its use in controlling epilepsy is available.
More recently, a number of patients
with both focal and generalized intractable seizures have undergone
implantation of a nerve stimulator around the left vagus nerve.
Less than half experienced a >50% reduction in seizure frequency
and only the rare patient became seizure free.(30) The number
of cases is limited as is the follow up and therefore no definitive
conclusions can be made regarding this technique.
The success or failure of the surgical
treatment of epilepsy depends in large part on the proper selection
and investigation of patients. Recent advances in imaging and
long term EEG monitoring have allowed for a greater accuracy in
the localization of the seizure focus with overall surgical results
better than those of the prior decades. Continued investigation
into the basic mechanisms of the epilepsies as well new forms
of medical and surgical therapy is necessary in order to help
the many patients with severe and disabling intractable seizures.
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- Table 1 - Presurgical Evaluation
Phase I - Non-invasive
a. Clinical examination
- SPECT (ictal)
- routine EEG
- 24 hour intensive video/EEG monitoring
d. Neuropsychological testing
e. Psychosocial evaluation
Phase II - Invasive
- 24 hour intensive video/EEG monitoring
- epidural electrodes
- subdural electrodes
- intracerebral electrodes
d. Neuropsychological testing
- intracarotid amobarbital test
- Table 2 - Therapeutic Surgical Options
- temporal (en bloc, anteromedial, selective amygdalohippocampectomy)
b. multiple subpial transections
a. cerebellar stimulation
b. vagal stimulation
- Figure 1 - Coronal T2-weighted MRI
demonstrating atrophy of the right hippocampus with accompanying
increased signal suggestive of mesial temporal sclerosis
- Figure 2 - Fluoro-deoxyglucose Positron
Emission Tomography revealing decreased metabolism in the right
temporal lobe especially in the medial portion
- Figure 3 - Lateral skull radiograph
demonstrating a large subdural grid of electrodes under the bone
- Figure 4 - AP skull radiograph revealing
the location of intracerebral electrodes placed into both the
frontal and temporal lobes from a lateral approach
- Figure 5 - Functional MRI of a young
man with a cavernous angioma and intractable focal motor seizures
of the right face and hand. fMRI demonstrates the lesion (yellow)
in the Rolandic cortex just inferior to primary motor cortex for
the hand (red)
- Figure 6 - Axial T1-weighted MRI
of a patient who has undergone a classical anterior temporal lobectomy
- Figure 7 - Coronal T1-weighted MRI
of a patient who has undergone a selective amygdalohippocampectomy