Te c h n i c a l N o t e Stereotact Funct Neurosurg 2007;85:6-10
Published online: October 30,2006
D O I : 1 0 . 11 5 9 / 0 0 0 0 9 6 6 3 3
A Simple Stereotactic Method for Frameless Deep Brain Stimulation M. SamEljameP MarkTulley^ KateSpillane^ Departments of ® Neurosurgery, ''Medical Physics and 'Neurophysiology, Ninewells Hospital and Medical School, Dundee, UK
Key
Words
Introduction
Deep brain stimulation • Microelectrode recording •
Parkinson's disease • Stereotactic techniques Exact placement of the deep brain stimulation (DBS) lead in the physiological target is a crucial step in functional neurosurgery to maximise benefits and avoid side Abstract
effects
of
t h e r a p y.
Although
recent
advances
in
neuro-
Background: Deep brain stimulation (DBS) is widely used to imaging and computer technology have made it possible treat advanced Parkinson's disease, other movement and to be more accurate in localising the target, a number of psychiatricdisorders. DBS implantation requires application factors can and do introduce a significant error. Head
of a stereotactic frame throughout a lengthy procedure, tremor and movement, inherent image distortion, inhermaking it uncomfortable and tiring. We designed a stereo- ent frame-related mechanical error, frame-related skull
tactic cube to stage the operation, perform frameless micro- distortion, brain shift with pulse, breathing and CSF electrode recording (MER) and fix the DBS. Methods: The drainage and human error during translation of frame 15-mm cube is implanted in a burr hole using bone cement, co-ordinates are just a few of the compounding factors It contains 5 parallel trajectories (central + 4 around). It is that reduce accuracy. In our own experience, physiologialigned by stereotactic frame so that central trajectory cal mapping of the anatomical target had modified the reachesthetarget. Frameless MER is performed by attaching final location of the active contact of the DBS in 67% a micro-driver to the cube using 2-5 cannulae (4 cm). The [1, 2], and in 12-13% [1, 3] the alteration was more than
DBS is fixed to the cube by a mini-plate and 1 screw. Ninety- 4 mm. Furthermore, performing frame placement, imagsix cubes were compared with 43 Bennet spheres (BS). Re- ing, planning, microelectrode recording (MER) and DBS suits: No cube moved compared to 2 (5%) BS (p < 0.05). The placements bilaterally is quite a lengthy procedure in final trajectory was central in 64.4% of cubes compared to many set-ups, and patients often express discomfort and 47.5% of BS, and the final target was >2 mm out in no cubes anxiety particularly if they were deprived of their usual compared to 12.5% of BS (p < 0.01). Infection and haemor- medication or kept nil by mouth. Of equal importance, rhage were observed in 2.5% and 3.3% of cubes, respective- securing the DBS lead at the end of a lengthy procedure ly, while 5% of BS developed infection, 5% haemorrhage and is difficult and often requires additional techniques to 7.5% skin erosion. Conc/us/ons; This method is simple and prevent lead migration or dislodgement. We have deeffective in staging DBS procedures, performing frameless signed and used a simple method to overcome most, if not MER and DBS implantation, fixation and revision. all, the shortcomings of the above-mentioned techCopyright ® 2007 S. Karger AG, Basel niqueS.
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©2007 S. Karger AG, Basel
M. Sam Eljamel
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Department of Neurosurgery, Ninewells Hospital and Medical School Dundee DD19SY(UK)
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Fig.l. The ETSC; face view and side view attached to the alignment stereotactic fork.
Fig. 2. Schematic representation of the ETSC. a 3-D schematic view, b 2-D sche matic view from the surface towards the surgeon.
Fig. 3. Intra-operative photograph of the micro-driver attached to the surface ETSC.
2
Materials and Methods
The ETSC stands for the Eljamel-Tulley Stereotactic Cube; it is a 10 X 10 X 15 mm cube (fig. 1) made of CT and MRI compat ible polytetrafluoroethylene or Teflon. The cube contains 5 paral lel tracks at 1.5 mm apart: central, anterior, posterior, lateral and medial (fig. 2). The ETSC is aligned using a stereotactic fork (fig. 1) and ordi
nary stereotactic frame so that the central track gives direct access
to the calculated anatomical target, using stereotactic software, fused MRI and CT and an electronic stereotactic atlas. The ste
reotactic fork is a passive aiming probe that holds the cube by a row of three 5-mm-long projections, which fit into the upper sur face of the ETSC. Once the cube is aligned within the burr hole, it is fixed using bone cement. The surgical incision is closed in layers in the usual fashion. The whole procedure of frame place ment, scanning and cube placement are performed under general anaesthesia.
A Simple Stereotactic Method for Frameless Deep Brain Stimulation
At a different day or when the patient has recovered from an aesthesia, the scalp incision over the ETSC is re-opened and the top of the ETSC is exposed under local anaesthesia. MER is per formed using a micro-driver (fig. 3) without the need for the frame or head fixation. The patient is simply brought into theatre and the MER and DBS implantation is performed without the need for a frame or head fixation. The micro-driver is fixed to the
ETSC by 2-5 short cannulae (4 cm in length). The micro-driver consists of a metallic base that mirrors the ETSC cube with 5 sim
ilar trajectories that allows it to be fixed tightly with the cannulae; full details of the micro-driver are demonstrated in figure 4. Al though it was possible to record from 5 simultaneous tracks, we
have only needed on average 3. The micro-electrodes are fixed in
the micro-driver and MER began 2 cm above the anatomical tar get and continued till the physiological target is mapped out. We have used our own micro-electrodes connected to Medelec Synergy System (Oxford Instruments, UK) [4] but the system can be used with other commercially available electrodes and MER equipment such as lead point. The final physiological position.
Stereotact Fund Neurosurg 2007;85:6-10
7
Table 1. Comparison of the ETSC and BS baseline data in 130 consecutive procedures Va r i a b l e
ETSC (n = 94)
BS (n = 43)
Age, years (range)
66.47 (29-70)
51.50 (22-69)
Male:female ratio
1.45
0.8
Parkinson's disease Essential tremor
49 (52.13%) 22 (23.40%) 12(12.77%) 10(10.64%) 1 (1.1%) 33 (35.11%) 50 (53.19%) 10(10.64%) 1 (1.1%)
15 (34.88%) 9 (20.90%) 17 (39.53%) 2 (4.65%)
Rubral tremor (MS) Dystonia Pain STN V I M
Gpi P V G
6(13.95%) 35 (81.40%) 2 (4.65%)
t
i .VJ
Ftg. 4. Schematic depiction of the micro-driver, a 3-D schematic presentation of the driver; 1 = advancement knob (with each one
Fig. 5. Photograph of the modified BS.
turn the microelectrode advances 1 mm); 2 + 3 + 8 = the driver
shaft; 4 = the microelectrode carrier which can be advanced by the knob; 5 + 6 = microelectrode holder; 7 = advancement track;
9 = 5 parallel trajectories mirror image of those on the ETSC; 10+11= the base that is fixed to the ETSC. b 2-D schematic view
then repeated and the lead was fixed to the ETSC by a bio-plate
of the lateral projection of the micro-driver.
and a single screw. The ETSC was used in 94 consecutive procedures. This was compared to 43 consecutive procedures previously performed us ing an earlier skull-fixed device, a modified Bennet sphere (BS) [1,3], which were performed just before the use of the ETSC. The details of these patients are summarised in table I. The modified BS consists of two metallic rings that fix a plastic sphere with two cut surfaces and 13 parallel trajectories (fig. 5). One ring fixes the BS to the skull via 3 screws, and when the two rings are tightened the aligned BS is fixed in position and ready to be used in a simi lar fashion as the ETSC. However, the BS is inevitably bulky and cosmetically unacceptable and had to be removed at the end of the DBS implantation; it is during the removal of the BS that lead dis placement can occur.
which gave the best clinical outcome was taken as the actual target location, and for the purpose of comparison the difference be tween this final location and the anatomical target position was used as measurement of target deviation. Once the correct target was mapped, impedance measurements and macro-stimulation using 5 and 75 Hz was used to measure the response and look for side effects. The DBS was then inserted in the exact place so that the distal contact is located at the mapped target. Stimulation was
S t e r e o t a c t F u n c t N e u r o s u r g 2 0 0 7 ; 8 5 : 6 - 1 0 E l j a m e l / Tu l l e y / S p i l l a n e
Results
A total of 9 procedures were excluded from the analy sis because they did not proceed to DBS implantations, 6 ETSCs (6.4%) and 3 BSs (6.8%). Out of 90 ETSC, none
moved or migrated (0%) compared to 2 (5%) BS (p < 0.05). The DBS was implanted in the central trajectory in 64.4% of the ETSC group and in 47.5% in the BS group. The final trajectory was anterior in 7.5%, lateral in 8.5%,
posterior in 14.9% and medial in 4.7% of the ETSC group compared to 15% anterior, 7.5% lateral, 20% posterior and 10% medial in the BS group (p < 0.05). The final tar
get was more than 2 mm out in none (0%) of the ETSC group compared to 12.5% in the BS group (p < 0.01). Complications encountered included infection, intracra nial haemorrhage and skin erosion. Infection occurred in 2.5%, haemorrhage in 3.3% and no skin erosions in the ETSCs, whilst 5% of the BSs developed infection, 5% haemorrhage and 7.5% skin erosion. Revisions were re quired in 2.2% of the ETSC and 5% of the BS.
Discussion
High-frequency stimulation of the subthalamic nucle us, the globus pallidus internus and the thalamus using DBS leads is a widely used treatment to control Parkin son s disease, dystonia and tremor [5-8]. However, its ef fectiveness is dependent on precise placement of the con tact in the functional target and its fixation to the skull to prevent lead migration and displacement. In a recent paper on long-term complications of DBS, overall, 25.3% of patients had hardware-related complications involving
the ETSC under general anaesthesia for comfort to the patient and for obtaining images without any distortion or movement artefact. By staging the operation, we have shortened the time needed for the patient to be awake
without medication to an average of 90 min (range 60120 min). Moreover, precise anatomical localization of the functional target is bugged by inherent image distor tion, which can be reduced by image fusion but not com pletely vanished [1, 4] by frame errors of mechanical or translational nature which can be due to imaging error
alone [10], and by brain shift and CSF escape during a lengthy procedure. In our series, the use of the 5 parallel trajectory design had overcome these small errors intro duced by all these factors, as we found that in 35.6% the final DBS placement was not in the central trajectory. This is similar to previously reported studies where MER had altered the final DBS placement in a significant num ber of patients [1-3]. Previous efforts to overcome these inaccuracies led to the development of the modified BS, the BS had to be removed at the end of DBS implantation
and therefore was prone to lead displacements and revi sions requiring re-scanning and frame placement. Fur thermore, we found that the BS was more prone to skin erosion and sphere movement. However, the ETSC had outperformed the modified BS in that the trajectory was central in 64.4% compared to 47.5% of BS. While there was no DBS implanted more than 2 mm away from the anatomical target in the ETSC group, 12.5% were >2 mm
from the anatomical target in the BS group. Scalp erosion and sphere movements were unwanted complications specific to the BS; the other complications encountered were not specific to either group and the difference was not statistically significant.
23 (18.5%) of the electrodes. These included 4 lead frac
tures and 4 lead migrations. Lead migration and fracture would require revision and it is therefore desirable to pre vent lead migration and develop an easy way to revise the fractured leads without re-imaging and mapping the tar get. The hardware-related complication rate per elec trode-year was 8.4% [9]. In our series, none of the 90 leads migrated in the ETSC group and the two leads, which re quired revision due to lead fractures or short circuiting, were revised without the need for re-imaging. Further more, the average operative time to implant a DBS is
about 5.8 h (range from 2.1-10 h) [9], which can be daunt ing to the patient particularly when deprived of food, wa ter and anti-Parkinson's medication, and can be daunting to the surgical team if the surgery exceeds the expected working time. Using the ETSC had allowed us to stage the operation more easily, obtain the images and implanting
Conclusion
The ETSC method is simple and effective in staging DBS procedures, performing frameless MER and DBS implantation, fixation and revision.
Acknowledgements We would like to thank all the staff in the neurosurgical de partment, neurosurgical operating room, the medical physics de partment and the neurophysiology department for their support during these procedures.
A Simple Stereotactic Method for Stereotact Funct Neurosurg 2007;85:6-10 9 Frameless Deep Brain Stimulation
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