Movement Disorders
13th Meet World Soc Stereotact Funct Neurosurg, Adelaide 2001
Stereotact Funct Neurosurg 2001;77:87–90
DOI: 10.1159/000064602
Targeting the Subthalamic Nucleus
T.Z. Aziz a, b, d D. Nandi a S. Parkin c X. Liu a N. Giladi a
P. Bain d R.G. Gregory c C. Joint b R.B. Scott b J.F. Stein a
a University
Laboratory of Physiology; Departments of b Neurosurgery, and
Radcliffe Infirmary, Oxford, and d Department of Neurology,
Charing Cross Hospital, London, UK
c Neurology,
Key Words
Subthalamic nucleus W Targeting W Lesions W Stimulation W Parkinson’s
disease
Abstract
The small size and surrounding neuronal structures and fibre tracts
make the STN a difficult stereotactic target. In this article we present the
technique used by us to target the STN. Our combined experience from two
centres comprises 18 lesions and 27 stimulator implants in the STN. Our
criteria for patient selection and the use of MRI, frame-on CT and volumetric
image fusion are presented. The role of a movement disorder specialist
neurologist in the operating theatre, local field potential recording, impedance monitoring, macrostimulation, post-operative CT/MRI and test stimulation are detailed.
Copyright © 2002 S. Karger AG, Basel
Introduction
Since the demonstration in parkinsonian sub-human primates that lesioning
the subthalamic nucleus (STN) could alleviate the cardinal signs of Parkinson’s
disease [1–3], the STN has been adopted by many groups as the target of choice.
ABC
© 2002 S. Karger AG, Basel
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Dr. T.Z. Aziz
Department of Neurosurgery, Radcliffe Infirmary
Woodstock Road, Oxford OX2 6HE (UK)
Tel. +44 1865 228 425, Fax +44 1865 224 898
E-Mail tipuaziz@btinternet.com
Given the small size of the target and the fact that it is encased in critical fibre
tracts, many techniques have been adopted to safely approach this region. We
present the technique used in the Radcliffe Infirmary, Oxford, and Charing Cross
Hospital, London. We have experience of 18 STN lesions and 27 STN stimulator
implants between the two sites from March 1998 to the present.
Minimal Requirements
For imaging, the basic requirements are an MRI scanner, a CT scanner and a
CT compatible stereotactic frame (we use the Radionics CRW frame). We also
routinely use software to volumetrically fuse MRI scans to the stereotactic scan
which is very useful, but not critical. Personnel at each centre consists of an experienced stereotactic neurosurgeon, a neurologist experienced in movement disorders, a neuroanaesthetist, a neurophysiologist, a neuropsychologist and a specialist movement disorders nurse.
Patient Selection
The best outcomes will be obtained only if the right patients are offered surgery, and here the experience of the neurologist is critical. We offer surgery to
patients with true idiopathic Parkinson’s disease who are very L-Dopa responsive, with no drug-resistant symptoms of ‘on’ freezing, frequents falls, poor balance, bulbar symptoms of low speech volume and poor swallowing, cognitive
impairment, hallucinations on medication and unreal expectations of surgery.
Although drug reduction is claimed to be one of the major advantages of STN
surgery [4–6], we do not routinely pursue this goal unless the patient is young with
early complications of L-Dopa therapy.
Surgical Technique
Pre-operatively patients undergo a T2 weighted axial MRI scan, parallel to
the AC-PC plane in 3.0 mm contiguous slices. Patients may need intravenous
sedation or even a general anaesthetic for this scan depending on the predominant
symptomatology.
Surgery is performed with the patient off all medications overnight. Given
their disabilities, these cases are always first on the operating list. The base ring of
the stereotactic frame is fitted to the skull under general anaesthesia and a stereotactic CT scan of the whole head aligned parallel to the orbito-meatal line and in
3.0 mm contiguous slices is obtained. The patient is then transferred back to the
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2001;77:87–90
Aziz/Nandi/Parkin/Liu/Giladi/Bain/Gregory/
Joint/Scott/Stein
theatre, positioned supine on the table with the base ring fixed to the table and
woken up after insertion of an arterial line to monitor blood pressure, which is
maintained at normal pre-operative levels with hypotensives if necessary. When
awake the attending neurologist confirms the patient is fully co-operative and the
physical signs are present.
Using Image Fusion and Stereoplan, the coordinates of the subthalamic
nucleus are calculated. To do so we draw an imaginary line across the anterior
limits of the red nucleus and choose as the target the hypointense region lying
between the red nucleus and the cerebral peduncle. In relation to the mid-commissural point this lies usually 4.0 mm posterior, 10–12 mm lateral and 5 mm
below it. A trajectory is planned to avoid transgressing the lateral ventricles.
We do not shave the patient’s head but wash the hair with aqueous and then
alcoholic chlorhexidine and infiltrate the line of incision with 0.25% bupivacaine.
The co-ordinates are transferred to the frame and checked against the phantom
and fixed to the base ring.
Through a linear scalp incision for neurostimulation or a punctate incision
for lesioning, a 2.7 mm twist drill is performed just anterior to the coronal suture
and lateral enough to avoid the lateral ventricle. The initial exploration is made
with a Radionics TM electrode with a 2.0-mm-exposed tip and 1.8 mm diameter,
both to confirm clinical effects prior to lesioning or to create a tract for the deep
brain electrode for neuromodulation. In the region of the STN the impedance as
measured by this electrode is 600–700 ø. Stimulation at 100 Hz, 1.0 ms pulse
width and abolition of contralateral parkinsonian signs of rigidity, bradykinesia
and tremor at 0.5–1.5 V and no capsular effects at 2.0 V and 2 Hz confirms it is
safe to lesion. A temporary lesion is then made for 60 s at 45 C to confirm this. If
so three lesions are placed for 60 s and at 75 C, 2.0 mm beyond, at and 2.0 mm
above target. Lesions are always performed unilaterally at one sitting.
Exploration for neurostimulation with the TM electrode is performed at
150–180 Hz, 0.1 ms pulse width with clinical effect observed at 1.5–2.0 V with no
side effects at twice the clinically effective amplitude. The TM electrode is then
replaced with the permanent DBS electrode and on table bipolar stimulation and
field potential recording performed. Those set of electrodes with greatest coherence with EMG recordings are chosen to lie in the middle two of the four electrodes of the Medtronics 3389 electrode. The electrode is then gently fixed to the
skull with a mini-plate and field potentials and effects of stimulation checked
again to confirm identical effects and hence no shift in position. The electrode is
then externalised to allow for a week of clinical assessment of effect. If confirmed
and a postoperative CT scan shows good localisation, then the following week the
patient is anaesthetised and full implantation of the extension cable and pacemaker is performed subcutaneously below the clavicle. Because of our experience
of global confusion that can attend very occasionally patients with simultaneous
Targeting the Subthalamic Nucleus
Stereotact Funct Neurosurg
2001;77:87–90
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bilateral STN implants, we usually implant one electrode initially but also pass a
contralateral extension cable under the scalp to make contralateral surgery
straightforward at a later date.
Conclusions
The technique presented is that practiced in our units and the conclusions
drawn also are very personal. We have abandoned STN lesioning generally
because of short-lived benefits. We have also noted that post-pallidotomy and
thalamotomy patients do not benefit significantly from STN stimulation on the
same side.
Our clinical experience is that not all patients benefit from the STN as a
target and therefore still offer thalamic and pallidal surgery, be it lesional or stimulation, as clinical and social reasons dictate.
Acknowledgements
D.N. is supported by the Norman Collisson Foundation and T.Z.A. by the Medical
Research Council, UK. N.G. is a McDonal Pew fellow in Oxford University from the Movement Disorders Unit of Tel-Aviv Medical Centre in Israel.
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Stereotact Funct Neurosurg
2001;77:87–90
Aziz/Nandi/Parkin/Liu/Giladi/Bain/Gregory/
Joint/Scott/Stein