Vol.2, No.7, 753-758 (2010)
Copyright © 2010 SciRes. Openly accessible at http://www.scirp.org/journal/HEALTH/
Neuronavigation and epilepsy surgery
Martin B. Glaser1*, Konrad J. Werhahn2, Peter Grunert1, Clemens Sommer3,
Wibke Müller-Forell4, Joachim Oertel1
1Department of Neurosurgery, Unive rsity Hospital Medical Cente r, Johannes Gutenberg University, Mainz, Germany;
*Corresponding Aut hor: glaserm@uni-mainz.de
2Department of N e urology, University Hospital Medical Center, Johannes Gutenberg University, Mainz, Germany
3Department of Neuro p a th o l o gy, University Hospital Medical Center, Johannes Gutenberg University, Mainz, Germany
4Institution of Neuroradiology, University Hospital Medical Center, Johannes Gutenberg University, Mainz, Germany
Received 16 February 2010; revised 11 March 2010; accepted 12 March 2010.
Resective epilepsy surgery is an elective ther-
apy indicated in focal epilepsy patients who are
resistant to pharmacotherapy. Every effort sho-
uld be undertaken to perform the procedures as
safe and less traumatic as possible. Neurona-
vigation could represent a suitable tool to re-
duce surgical morbidity and increase surgical
radicality. Here, we present a series of 41 pa-
tients who were operated on for medically in-
tractable epilepsy using neuronavigation. Over-
all, complication rate was 17% with a favourable
seizure outcome of 88% (Engel’s class I/II). Our
data suggest that neuronavigation is a valuable
surgical technique to accomplish a favourable
outcome in epilepsy surgery.
Keywords: Neuronavigation; Epilepsy Surgery;
Epilepsy is a frequent condition. Approximately 40 mil-
lion people are affected worldwide and the prevalence of
epilepsy has been estimated to be around 0.7% [1]. The
mean annual incidence of first unprovoked seizures in
population-based studies is 56.8 per 100 000 person-
years, 23.5 per 100 000 person-years for single unpro-
voked seizures, and 33.3 per 100 000 person-years for
epilepsy (recurrent unprovoked seizures). Partial sei-
zures occur in 40-60%, two-thirds of which are temporal
lobe epilepsies [2,3]. Clinically, focal epilepsy may first
be suspected with a first witnessed report of a general-
ized tonic-clonic seizure but often seizures may be more
subtle consisting of a transient short lasting loss of con-
sciousness with or without oral or manual automatisms
or focal tonic or clonic movements affecting parts of the
body. Seizures may lead to developmental retardation,
social impairment (e.g. limited choice of profession,
ability to obtain a driving licence) and even sudden un-
expected death in epilepsy [4]. In most cases, conserva-
tive treatment with antiepileptic drugs is successful in
preventing clinical seizures, but up to 33% of patients
will prove to be resistant to medical treatment [5].
Patients with focal epilepsy are generally surgical
candidates, if medical treatment with at least two differ-
ent anticonvulsive drugs in sufficient doses fails and
disabling seizures persist. Bad prognostic factors for
medical treatment in focal epilepsy are a structural lesion
on Magnetic Resonance Imaging (MRI), particularly
with dual pathology, post-stroke scars and vascular mal-
formations having the best and cortical dysgenesis and
hippocampal sclerosis the poorest outcome [3]. Optimal
surgical results are obtained in patients with a circum-
scribed seizure onset (especially temporal/temporome-
sial) in video-EEG recordings, concordant focal pathol-
ogy on MRI (e.g. hippocampal sclerosis) and concordant
neuropsychological findings [6,7].
The need for a device enabling precise introduction of
instruments into deep intracerebral structures was first
addressed by Zernov et al. [8] 1890. He constructed a
frame which was fixed on the skull by screws. The posi-
tion of deep structures were measured from external
anatomical landmarks. Clark developed 1908 a frame
which served as a stable coordinate system for calcula-
tion of intracranial targets in relation to the frame [9,10].
In the second half of the last century these frames were
refined. More and more indications were found along
with the progress of the imaging modalities (x-ray, an-
giogram, computed tomography, MRI). Frame based
stereotactic systems are still the most accurate naviga-
tional tools and very small targets like the subthalamic
nucleus can be implanted with depth electrodes for the
treatment of parkinsonism.
M. B. Glaser et al. / HEALTH 2 (2010) 753-758
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One major disadvantage of the stereotactic frame is
the restricted surgical field as long as the arc is in place.
At the end of the 1980s the “frameless” navigation was
developed, with first clinical applications in neurosur-
gery at the beginning of th e 1990s [11].
Nowadays, frameless neuronavigation is an accepted
tool in contemporary microneurosurgery [12-15]. Its
application contributes to make surgical approaches
smaller and less invasive [16]. Consequently neuronavi-
gation was integrated also in epilepsy surgery [17].
The neuronavigation is basically a miniature of a GPS
(general positioning system). The neuronavigation sys-
tems are able to determine the position of the tip of a
pointer in 3-D-space and to transfer the position into the
appropriate CT or MRI data set in real time during the
entire operation (in case of a microscope the focus cor-
responds to the tip of the pointer). From the technical
point of view we can distinguish between armbased and
armless navigation. The latter have the advantage not to
restrict the operative field. Different armless systems
were realized using sonic, infrared, magnetic waves or
visible light (see Figure 1). The transfer of the pointer
tip in the appropriate images makes a registration before
application necessary. Per point registration and surface
registration were developed for this purpose. The navi-
gation devices have higher flexibility but less accuracy
in comparison to the frame based systems. Regarding
navigation accuracy we have clearly to distinguish be-
tween technical accuracy of the navigation system (how
accurately the system determines the position in the 3-D-
space), registration accuracy (how accurately is the data
transfer from 3-D-space into the CT and MRI image
space) and application accuracy depending of the intra-
operative situation including brain shift [18].
Figure 1. Drawing of an armless neuronavigation system setup.
For this study, we reviewed our surgical cases that
were performed for pharmacoresistent focal epilepsy
using a neuronavigation device.
In our retrospective study, we gathered the clinical data
of all patients who had navigation assisted surgery for
medically intractable epilepsy. We evaluated the charts
of 41 patients who were treated in our institution from
09.2003 to 08.2009 and reviewed the postoperative
clinical follow up as well as neuro-imaging data for the
degree of resection and complications.
Initially we used the Optical Tracking System (OTS®,
Radionics, Burlington, Massachusetts, USA). In 31 cases,
we navigated with the BrainLAB® System (BrainLAB,
Heimstetten, Germany) and in a further 9 cases with the
SonoWand® (Mison, Trondheim, Norway).
In frameless Neuronavigation, after general anaesthe-
sia has been induced and immediately before surgery the
patient’s head is fixed in a three point fixation device
and then referenced to the presurgical MRI (or other
imaging modality such as computed tomography) by
indicating to at least 4 defined landmarks so that the
navigation system may locate the patient´s head in the
three dimensional space. Hereafter the patient´s individ-
ual anatomy is shown on a monitor according to the re-
gion where a pointer is held on. The surgeon sees exactly
where the targeted lesion is in relation to the skull sur-
face to place the craniotomy on the ideal site. Moreover,
he may check the position of his instrument any time
during surgery.
For selective amygdala-hippocampectomies, we used
a supraorbital craniotomy via a subfrontal approach [19].
Temporal pole resections with amygdala-hippocampec-
tomies were approached via a small anterior temporal
craniotomy (diameter approx. 2.5 cm). For extratempo-
ral lesionectomies neuronavigation was also employed to
gain direct access with craniotomies as small as possible.
“Keyhole” approaches were applied when possible, es-
pecially in deeper seated lesions.
This series includes 41 consecutive patients with phar-
macoresistent focal epilepsy with a mean age of 36 years
(15-70 years). There were 17 male and 24 female indi-
viduals. The mean duration of the epilepsy was 15.8
years. Most patients suffered from mesial temporal lobe
epilepsy (n = 28, 17 left/11 right). All of them had been
transferred from the department of neurology of the
University Medical Center, Mainz, after video-EEG-
monitoring for identification of the seizure onset region,
M. B. Glaser et al. / HEALTH 2 (2010) 753-758
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correlation with the neuro-imaging and neuropsycholo-
gical testing. Histological findings showed hippocampal
sclerosis in 21 specimens. The remaining 7 had no spe-
cific changes (no abnormality, dysplasias, corpora amy-
The extra-temporomesial pathologies consisted of 4
gangliogliomas, 1 gangliocytoma, 2 astrocytomas, 1
oligoastrocytoma, 2 cavernomas, 1 gliosis after hemor-
rhage from an AVM, 1 dermoid and 1 meningeoma (6
left/7 right).
The surgery for the mesial temporal lobe epilepsy pa-
tients consisted of 2 selective amygdalahippocampecto-
mies via a supraorbital subfrontal approach. The re-
maining 27 cases had an anterior temporal craniotomy
for pole resection and amygda l ah i pp ocampectomy.
The extratemporal pathologies were approached by
the shortest or least traumatic way concerning the pa-
tient´s neurological function. On the BrainLAB planning
station, it is possible to determine the trajectory and im-
port the information of the presurgical MRIs into the
intraoperative surgical field.
In the operating room neuronavigation was installed
after fixation of the patient’s head in the Mayfield clamp.
Accuracy was checked by correlation with anatomical
Figure 2. View of the hippocampus through the navigated
landmarks after referencing the patients head with the
preoperative 3-D-MRI data set either by laser or land-
mark registration (at least 4 points; mostly nasion, lateral
orbital rims and upper helix attachments).
Neuronavigation was used to gain direct access to the
pathological structures. This was achieved generally by
use of a pointer. Additionally the microscope (Pentero or
NC4, Carl Zeiss, Oberkochen, Germany) itself could be
registered and navigated with the BrainLAB system. It
was especially helpful in the amygdala-hippocampec-
tomies in opening the temporal horn of the lateral ven-
tricle to enable the dissection of the hippocampus. The
viewing direction could be brought in the planned tra-
jectory to reach the targeted structure. When the target is
displayed in the ocular of the microscope, it is not nec-
essary for the surgeon to place a pointer in the surgical
field and look up to the monitor of the navigation sys-
Finally the neuronav igation was then used to “define”
the extent of resection of the hippocampus. It was in-
tended to remove it at least to the dorsal edge of the
cerebral peduncle.
For all patients, site of surgery, duration between com-
pleted anaesthesiological preparation and skin incision
as well as the time for the surgery itself, blood loss, ICU
stay, hospital stay, neurological detoriation after surgery,
degree of resection and seizure outcome were collected.
The follow up of the patients and the classification
concerning Engel’s epileptological outcome classes [20]
were provided by the referring neurological department
(KJW). Mean follow up time was 23 month.
Installation and usage of the neuronavigation systems
was possible in all procedures. Average patient prepara-
tion (positioning, head fixation, referencing the neuro-
navigation, shaving, skin prepping, sterile draping) took
37 minutes. Mean duration of surgery was 209 minutes
from skin incision to wound closure. The mean ICU stay
scored 20.3 hours, the mean hospital stay 8.5 days.
There was an average blood loss of 310 cc per co mplete
procedure. Not a single bl ood pr o duct was ad ministered.
There was no mortality in this series. The following
complications were noted: One patient had a space oc-
cupying frontal epidural haematoma on his routine
postoperative cranial computed tomogram which was
clinically asymptomatic but evacuated for its size. Two
patients showed a slight hemiparesis caused by small
thalamic ischemias. They regained full strength but still
M. B. Glaser et al. / HEALTH 2 (2010) 753-758
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have a deficit in fine motor skills. A further two patients
had incomplete oculomotor palsies which resolved
without sequelae. One patient developed a severe gener-
alized vasospasm 10 days after subtotal frontal lobec-
tomy. He has no focal neurological deficit but a relevant
lack of motivation.
One rhinoliquorrhoea occurred after a supraorbital
approach via the opened frontal sinus. The liquorrhoea
ceased after temporary lumbar drainage.
Postsurgical imaging showed complete removal of the
extratemporal pathologies in 9 of the 13 cases. The de-
gree of hippocampal resection was noted in relation to
the brain stem: a relatively short resection of the hippo-
campus only to the middle of the cerebral peduncle was
performed in 5 cases, to the dorsal margin of the cerebral
peduncle in 20 cases and in a further 3 cases beyond.
The neuronavigation was sufficiently exact in all
cases at the beginning of the procedure. Accuracy was as
reliable with laser patient registration as with registration
via anatomical landmarks. The calculated mean devia-
tion was 1.7 mm. It was possible to reach all lesions/
structures that were aimed for. It was extremely helpful
in localization of the temporal horn in amygdala-hippo-
campectomies. Neuronavigation overestimated the de-
gree of resection of the hippocampus, possibly due to
brain shift after CSF loss-especially after opening of the
lateral ventricle.
Postoperative seizure outcome was favourable after
amygdala-hippocampectomy with 21 patients Engel’s
class I and 6 patients Engel’s class II. One patient was
seizure free for 3.5 years and developed pharmacoresis-
tent temporal lobe epilepsy again so that re-resection is
being considered.
In the patients group with the extratemporal resections,
11 patients became seizure free (Engel’s class I). Two
patients did not profit at all and have still the same sei-
zure frequency in comparison to the presurgical state
(partial tumor resections).
In total, antiepileptic drugs were discon tinued in 8 pa-
tients and reduced in 5. The majority of 29 patients is
still under medication, similar to presurgical status.
For decades, atraumatic surgery for medically refractory
epilepsy has been the objective in order to improve pa-
tients functions and at the same time effectively reduce
seizures. Neuronavigation contributes to that aim by
minimizing the craniotomies and reach the target in the
planned trajectory [13].
On the other hand, there are only few publications
concerning neuronavigation and resective epilepsy sur-
gery [17,21-25].
Previous reports on neuronavigation in epilepsy sur-
gery were published without discussing its advantages
and pitfalls or without giving any clinical data [26-28].
Wurm et al. [24] published the largest series of 140
patients who underwent surgery for medically intractable
epilepsy. After the procedure for miscellaneous patholo-
gies surgeons answered a questionnaire to assess the
impact of the neuronavigation. They concluded that the
application of the navigation system was effectively and
safe in terms that the targets, even small in size, could be
located precisely and electrodes could be placed accu-
rately as well. Moreover the approach could be indi-
vidually tailored.
In a previous series of Oertel et al. [22] neuronaviga-
tion seemed to be helpful in avoidance of complications
(8% vs. 22%). In 93% the surgeon rated the application
of the neuronavigation as “helpful”.
A comparison of the complications in various studies
is compiled in Table 2, seizure outcome in Table 3.
In our series complication rate and seizure outcome
are comparable to larger series [29]. The application was
safe. There were no complications with direct referral to
the use of the navigation system. The time for prepara-
tion of the navigation was acceptable: in our evaluation
the total time from anaesthesia induction to skin incision
was 37 minutes. In comparison to that the installation of
the neuronavigation equipment alone took additional 26
minutes in another study [30]. Surgery itself was not
Table 1. Usefulness of neuronavigation.
Presurgical pla nni ng /st rategy Helpful for studying patients indiv idual anatomy
Determination of craniotomy si te Helpful, especially over convexity
Locating lesions Helpful, especially in subcortical p ath olo gie s
Amygdala-hippocam pectomies Extreme helpful in access the temporal horn
Resection control Var i a ble (brain shift), often overestimation, consider alternatives ( e.g. ultr asound )
Delicate site of surgery Helpful, shows eloquent structu res as well
M. B. Glaser et al. / HEALTH 2 (2010) 753-758
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Table 2. Epilepsy surgery and complications (perm. = permanent; trans. = transient).
Complications Acar et al. Oertel et al. Cho et al. Glaser et al. Sindou et al. without Navigation
CSF fistula 2 trans. 1 trans.
Visual field defects 4 perm. Not investigated 1 4 perm. Not investigated
CN palsy 1 trans. 2 trans.
Motor deficit 1 perm. 1 trans. 2 trans. 2 perm.
Aphasia 1 trans. 1 perm. 1 trans.
Postop. haematoma 1 1 3
Infection 3
n = 39 n = 38 n = 46 n = 41 n = 100
Table 3. Seizure-outcome after epilepsy surgery.
Engel’s class Acar et al. Oertel et al. Cho et al. Glaser et al. Sindou et al. without Navigation
I 37 (95%) 20 (53%) 28 (61%) 32 (78%) 85 (85%)
II 2 (5%) 10 (22%) 4 (10%) 9 (9%)
III 6 (13%) 2 (5%) 2 (2%)
IV 2 (4%) 3 (7%) 4 (4%)
n = 39 n = 38 n = 46 n = 41 n = 100
Based on these results and our experience in the use of
neuronavigation, we conclude that the application of a
navigation system in epilep sy cases is safe and helpful in
finding the targeted structure and in minimizing trauma
to the patient by smaller craniotomies.
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