Keywords
anterior thalamic nucleus - deep-brain stimulation - pneumocephalus
Introduction
Deep-brain stimulation (DBS) is a standard treatment modality for movement disorders
such as Parkinson's disease, tremor, dystonia, and drug-resistant epilepsy.[1]
[2]
[3] The success of DBS surgery depends on precise electrode placement at the tentative
target, which is predetermined based on preoperative anatomical imaging. However,
intraoperative brain shift—that is, brain tissue displacement owing to pneumocephalus
and cerebrospinal fluid (CSF) loss during surgery—is a well-recognized cause of reduced
targeting accuracy.[4]
[5] While various approaches have been suggested,[6]
[7] no definitive solution to this problem has been established in clinical practice.
Herein, we introduce the half burr-hole technique, a novel method developed to minimize
brain shift during DBS targeting the anterior nucleus of the thalamus (ANT). In this
technique, the burr-hole is drilled to half the normal skull thickness, followed by
a twist-drill perforation and dural opening using monopolar cautery, which helps minimize
CSF leakage. Furthermore, the Stimloc system is compatible with this technique, providing
reliable postoperative electrode fixation.
Case Presentation
Case Illustration
The patient was a 28-year-old Japanese man with drug-resistant epilepsy who initially
presented with focal impaired awareness seizures (FIAS) 20 years ago. The patient's
clinical history is summarized in [Table 1]. Neurological examination revealed no abnormalities, and the patient's cognitive
function was intact. There were no comorbid conditions, and the patient had no history
of previous surgeries. Antiepileptic medication was initiated 12 years after onset,
resulting in good seizure control after 1 year. However, FIAS recurred 5 years ago,
prompting a referral to our hospital the following year. Weekly seizures persisted
despite medication adjustments, prompting bilateral temporal lobe stereo-electroencephalography
evaluation 6 months ago. Focal resection was deemed unfeasible based on the intracranial
recordings, which indicated that seizure onset originated from the lateral aspects
of both temporal lobes. Consequently, ANT-DBS was selected as the treatment approach.
Since ANT-DBS electrodes are implanted via a transventricular approach, there is a
high risk of brain shift due to CSF leakage, which may compromise the accuracy of
electrode placement. Therefore, this technique was selected.
Table 1
Clinical course to date
|
Age (y)
|
Clinical course
|
|
8
|
Onset of focal impaired awareness seizures (FIAS)
|
|
20
|
Initiation of antiepileptic drug (AED) therapy (12 y after onset)
|
|
21
|
Seizure control achieved after 1 y of treatment
|
|
23
|
Recurrence of FIAS
|
|
24
|
Referred to our hospital
|
|
28
|
Weekly seizures persisted despite multiple medication adjustments
|
|
27.5
|
Underwent bilateral temporal lobe stereo-electroencephalography
|
|
–
|
Seizures identified as originating from both lateral temporal lobes; resection unfeasible
|
|
28
|
ANT-DBS selected as the treatment approach
|
Abbreviations: ANT, anterior nucleus of the thalamus; DBS, deep-brain stimulation.
This study was approved by the Ethics Committee of Nishi-Niigata Chuo National Hospital.
Written informed consent to participate in the study was obtained from the participant.
Technique
Preoperative determination of the tentative target (the ANT) and insertion trajectory
was performed using the ROSA planning software (Zimmer Biomet, Warsaw, Indiana, United
States; [Fig. 1]).
Fig. 1 Coordinates of the tentative target (anterior nucleus of the thalamus, ANT) and insertion
trajectory were determined using the ROSA planning software (Zimmer Biomet; Warsaw,
Indiana, United States).
On the day of surgery, a Leksell frame was mounted on the patient's head using four
pins, followed by cranial imaging using a computed tomography (CT) suite. In the operating
room, the patient was positioned flat, and the cranial CT data were registered into
the ROSA ONE robotic system (Zimmer Biomet).
Using the robotic arm of the system, the electrode insertion sites were marked bilaterally
in the frontal region, 4-cm skin incisions were made, and the insertion points were
re-marked on the exposed bone surface. Initial partial burr-holes were made to a planned
depth of approximately 8 mm, with penetration controlled using a rubber ring attached
to the drill adapter as a stopper, in tandem with a perforator guard (PG01: S & Brain
Corporation, Tokyo, Japan; [Fig. 2A]). Subsequently, a specialized trephine (Rescue Round Cutter, SPD103: S & Brain Corporation)
was used to contour the stepped floor of the initial holes, enabling the attachment
of the Stimloc device (Medtronic, Minneapolis, Minnesota, United States; [Fig. 2B]).
Fig. 2 Surgical field image demonstrating the half burr-hole technique. (A, B). The initial partial burr-hole was drilled to a depth of approximately 8 mm, with
the perforation depth controlled using a rubber ring attached to the drill adapter
and a perforator guard (S & Brain Corporation, Tokyo, Japan) positioned on the cranial
surface, serving as stoppers. (C, D). The resulting hole had a stepped floor: it was contoured flat using a specialized
trephine (Rescue Round Cutter: S & Brain Corporation). (E) Stimloc bases were mounted onto bilateral half burr-holes. (F) The deeper cranial bone was perforated using a 2.4-mm twist drill. (G) The dura mater was penetrated and coagulated using an electrocautery device. (H) The insertion cannula was introduced. (I) The deep-brain stimulation (DBS) electrode was inserted and secured with the Stimloc.
Next, the ROSA guidance system was used again to mark the electrode insertion point.
The skull was perforated using a 2.4-mm twist drill ([Fig. 2C]), and the dura mater and cortical surface were cauterized using a specialized electrosurgical
scalpel. A catheter insertion needle (outer diameter: 2.1 mm; Elekta AB, Stockholm,
Sweden) was advanced to the target point, and a biological tissue adhesive (BOLHEAL
Tissue Sealant, KM Biologics, Kumamoto, Japan) was sprayed at the cortical entry point
to prevent CSF leakage. Frontal and lateral radiographs were obtained to confirm that
the position of the needle tip deviated < 1 mm from the tentative target. Subsequently,
the inner catheter was removed, and a directional lead with integrated stylet was
inserted (B33005M; Medtronic). The outer catheter was withdrawn, biological adhesive
was reapplied, and the lead was secured using the Stimloc device ([Fig. 2D]). The appropriate placement of the electrodes was confirmed through a second series
of intraoperative radiographs.
Following bilateral electrode placement, electrode impedance measurements and deep-brain
recordings were performed. Magnetic resonance imaging was performed 6 days after the
ANT-DBS surgery. Postoperative 3D-T1 images were imported into the ROSA planning software,
and the deviation between the actual position of the electrode tip and its preoperatively
planned position was measured. Postoperative CT examination revealed a pneumocephalus
volume of 0.46 cm3, indicating minimal CSF leakage. The electrodes were accurately placed near the planned
target coordinates.
Deviation measurements based on postoperative MRI showed that the right electrode
deviated by 0.31 mm medial, 1.40 mm anterior, and 1.11 mm superior, while the left
electrode deviated by 0.05 mm lateral, 0.16 mm anterior, and 0.21 mm inferior to the
preoperative plan ([Fig. 3]). The total time from skin incision to the creation of bilateral half burr-holes
was 32 minutes and from bilateral electrode placement to skin closure was 45 minutes.
The patient was discharged on postoperative day 8. Stimulation was initiated on postoperative
day 3 at 2(−)C(+) with 1.5 mA, 90 µs, and 145 Hz bilaterally. At the 3-month follow-up,
the stimulation intensity was increased to 3.5 mA. No stimulation-related adverse
effects, such as psychiatric symptoms or memory impairment, were observed. The surgical
wound showed no abnormalities. Prior to surgery, the patient experienced FIAS 20 to
30 times per week. Following ANT-DBS, the seizure frequency decreased to approximately
twice per week.
Fig. 3 Postoperative electrode location deviations from the preoperative ROSA plan. Postoperative
T1-weighted MRI shows electrode tip locations in axial, sagittal, and coronal views.
Top row (R): right electrode position with deviations of 0.31 mm medial, 1.40 mm anterior,
and 1.11 mm superior to the planned coordinates. Bottom row (L): left electrode position
with deviations of 0.05 mm lateral, 0.16 mm anterior, and 0.21 mm inferior to the
planned coordinates. The blue line represents the trajectory planned during preoperative
ROSA planning. The orange line corresponds to the actual electrode trajectory, reconstructed
based on the center of the hypointense region representing the electrode tip.
Discussion
The half burr-hole technique proposed in this study is designed to suppress brain
shift by minimizing CSF leakage using a small-diameter cranial and dural perforation.
In addition, by preserving the lower half of the skull at the burr-hole site, this
method eliminates the need for extradural hemostasis and sealing procedures typically
employed to prevent CSF leakage. Furthermore, lead fixation using the Stimloc system
is feasible with this approach, offering greater postoperative stability compared
to titanium microplates, thereby reducing the risk of electrode displacement.
DBS is commonly performed via the burr-hole technique, in which a cranial burr-hole
is created coaxially to the planned electrode trajectory. After dural incision and
visualization of the cortical surface, the electrode is inserted under stereotactic
guidance. However, intracranial pneumocephalus occurring during DBS surgery can lead
to brain shift, thereby impairing the precision of electrode placement.[8] Several factors have been implicated in brain shift, including CSF leakage, intraoperative
changes in intracranial pressure, and air influx into the cranial cavity.[4]
To address these concerns, multiple technical refinements have been introduced. These
include three-layer sealing of the arachnoid, pia, and cortex with fibrin glue,[8] burr-hole closure using polyethylene glycol-based sealants such as DuraSeal,[7] asleep DBS under general anesthesia,[9]
[11] and twist-drill craniostomy with a reduced diameter of 5 mm.[12] These approaches have significantly decreased pneumocephalus volume from 8 to 44 mL
using conventional methods to as little as 1.3 to 12 mL.[13] More recently, Zhang et al introduced a pneumocephalus-minimizing technique (PMT)
in which the dural opening is minimized and the burr-hole is sealed dynamically during
insertion using Gelfoam, resulting in a drastic reduction of pneumocephalus surface
area from 5.91 to 0.21 cm2.[11] We performed the procedure under general anesthesia with the patient's head maintained
in a flat position, limiting postoperative pneumocephalus to a minimal volume of 0.46 cm3.
We adopted a modified half burr-hole technique in which the lower portion of the skull
bone is preserved, thereby eliminating the need for postoperative burr-hole sealing.
This approach also simplifies extradural hemostasis and allows for accurate targeting,
even in cases with thick cranial bone or eccentric lead trajectories. Unlike conventional
methods requiring burr-hole enlargement in such situations,[10]
[14] our method reduces the need for re-drilling by utilizing stereotactic twist drilling.
Electrode fixation is achieved using the Stimloc anchoring system, which offers superior
stability compared to titanium microplate fixation, where greater postoperative displacement
has been reported.[15] Thus, this technique ensures secure lead stabilization and minimizes the risk of
migration.
As in Zhang's PMT,[11] direct visualization of cortical vasculature during lead insertion is not feasible.
However, the safety of this approach is supported by data indicating that selecting
an entry site more than 4 mm away from surface vasculature avoids hemorrhagic complications.
Our method utilizes a conservative 5-mm safety margin, which we believe provides comparable
safety. [Table 2] summarizes the technical differences between the conventional burr-hole, PMT, twist
drill, and the present half burr-hole technique.
Table 2
Comparison between the conventional method and the present technique
|
Item
|
Burr-hole technique
|
PMT technique
|
Twist drill Technique
|
Half burr-hole technique (this study)
|
|
Burr-hole diameter
|
∼14 mm
|
∼14 mm
|
∼3–5 mm
|
14 mm
|
|
Bone preservation
|
Full removal
|
Full removal
|
Perforation only
|
Lower half preserved
|
|
Dural penetration
|
Present
|
Minimally performed
|
Minimally performed
|
Minimally performed
|
|
CSF leak prevention
|
DuraSeal or PEG-based sealant
|
Dynamic sealing with Gelfoam
|
None
|
Fibrin glue
|
|
Pneumocephalus volume (ref.)
|
8–44 mL
|
0.21 cm2
|
Relatively low
|
0.46 cm3
|
|
Lead fixation
|
Titanium/plastic plate
|
Titanium/plastic plate
|
Plate or none
|
plastic plate
|
|
MER compatibility
|
◎ (multi-track possible)
|
△ (single-track only)
|
△ (single-track only)
|
△ (single-track only)
|
|
Extradural hemostasis required
|
Yes
|
Yes
|
No
|
No
|
|
Cortical vessel safety margin
|
Direct visualization
|
4 mm
|
Unclear
|
5 mm
|
We set the twist-drill perforation depth at 8 mm to ensure compatibility with all
lead clips currently approved in Japan. While the superficial diameter achieved by
the perforator reaches 14 mm, the deep diameter is limited to 11 mm, which may interfere
with the anchoring mechanism of some lead clips. To address this, a rescue cutter
is used to expand the deep-bone cavity; alternatively, a steel bar may serve as a
substitute when necessary.
This technique is suitable for cases in which the cranial bone is ≥ 10 mm thick and
multi-track MER is not essential.
Limitation
This case highlights the potential utility of the half burr-hole technique in ANT-DBS;
however, as a single case report, the findings should be interpreted with caution.
Further large-scale studies should validate its reproducibility, safety, and long-term
efficacy. If minor trajectory adjustments are required intraoperatively, they can
be addressed either by additional twist-drill perforation or by creating a full burr-hole
to the dura (PMT method).
Conclusion
The half burr-hole technique proposed in this study effectively suppresses CSF leakage
and minimizes brain shift. By preserving the lower skull margin at the burr-hole site,
this approach eliminates the need for extradural hemostasis and sealing procedures.
Furthermore, this technique allows for lead fixation using the Stimloc system, reducing
the risk of postoperative electrode displacement compared to titanium microplates.
