Unilateral Combined Stereotactic Radiofrequency Pallidotomy and Thalamotomy for Idiopathic Parkinson’s Disease

Abstract

BACKGROUND: Lesioning surgeries in Parkinson’s disease (PD) include target obliteration of a certain area in brain tissue to disrupt maladaptive neuronal arrangements. There was an advancement in treatment of movement disorders when stereotactic procedures were applied in lesioning. Target selections were modulated various times until in 1960s when thalamotomy was used for tremors and pallidotomy was used for bradykinesia and rigidity.
OBJECTIVE: To report the efficacy of unilateral combined stereotactic radiofrequency pallidotomy and thalamotomy for idiopathic Parkinson’s disease.
PATIENTS AND METHODS: This is a prospective observational study including 62 patients with idiopathic Parkinson’s disease who underwent stereotactic radiofrequency pallidotomy and thalamotomy between June 2017 and December 2019. Pre-operative clinical assessment was based on the Unified Parkinson’s Disease Rating Scale (UPDRS) and Hoehn and Yahr scale for PD. Postoperative clinical assessment was based on the UPDRS and Hoehn and Yahr scale for PD in addition to complications at 1, 6, 12 and 24 months.
RESULTS: Sixty patients who completed the two-year follow-up and fulfilled our criteria were recruited. The mean age was 57.47±9.90 years. The average UPDRS off state motor assessment results showed reduction after 1 month from 60.16 to 30.88, and at 24-months follow-up it was 41.6. The average Hoehn and Yahr scale was reduced from 3.63 to 1.19 after 1-month, and at 24 months it was 1.87. The average UPDRS constancy of tremors improved after 1-month from 3.53 to 0.75. Improvement in constancy of tremors reached 75% of cases after 24-months with average 1.62. The average UPDRS rigidity score improved at 1-month follow-up from 3.31 to 1.21. Total improvement of rigidity reached 63% after 24-months. Two patients had postoperative thalamic hematoma presenting with hemiplegia, which was conservatively managed, and improved after 1-month with little deficit. Around 51.6% of the patients had gait imbalance at 6-months follow-up while 22.5% showed dysarthria immediately postoperatively which totally resolved after 1-month in 12.9%. There were no recorded cases of infection, cerebrospinal fluid (CSF) leaks or cognitive dysfunction.
CONCLUSION: Our data suggest that unilateral combined stereotactic radiofrequency Pallidotomy and Thalamotomy for idiopathic PD is an effective procedure.
KEYWORDS: Pallidotomy, Parkinson’s, Radiofrequency, Spasticity, Thalamotomy, Tremors.

Full text

139
Volume 18, No. 2, December 2023
Original Article
BACKGROUND: Lesioning surgeries in Parkinson’s disease (PD) include target obliteration of a certain area in brain tissue to
disrupt maladaptive neuronal arrangements. There was an advancement in treatment of movement disorders when stereotactic
procedures were applied in lesioning. Target selections were modulated various times until in 1960s when thalamotomy was
used for tremors and pallidotomy was used for bradykinesia and rigidity.
OBJECTIVE: To report the ecacy of unilateral combined stereotactic radiofrequency pallidotomy and thalamotomy for
idiopathic Parkinson’s disease.
PATIENTS AND METHODS: This is a prospective observational study including 62 patients with idiopathic Parkinson’s
disease who underwent stereotactic radiofrequency pallidotomy and thalamotomy between June 2017 and December 2019.
Pre-operative clinical assessment was based on the Unied Parkinson’s Disease Rating Scale (UPDRS) and Hoehn and Yahr
scale for PD. Postoperative clinical assessment was based on the UPDRS and Hoehn and Yahr scale for PD in addition to
complications at 1, 6, 12 and 24 months.
RESULTS: Sixty patients who completed the two-year follow-up and fullled our criteria were recruited. The mean age
was 57.47±9.90 years. The average UPDRS o state motor assessment results showed reduction after 1 month from 60.16
to 30.88, and at 24-months follow-up it was 41.6. The average Hoehn and Yahr scale was reduced from 3.63 to 1.19 after
1-month, and at 24 months it was 1.87. The average UPDRS constancy of tremors improved after 1-month from 3.53 to
0.75. Improvement in constancy of tremors reached 75% of cases after 24-months with average 1.62. The average UPDRS
rigidity score improved at 1-month follow-up from 3.31 to 1.21. Total improvement of rigidity reached 63% after 24-months.
Two patients had postoperative thalamic hematoma presenting with hemiplegia, which was conservatively managed, and
improved after 1-month with little decit. Around 51.6% of the patients had gait imbalance at 6-months follow-up while 22.5%
showed dysarthria immediately postoperatively which totally resolved after 1-month in 12.9%. There were no recorded cases
of infection, cerebrospinal uid (CSF) leaks or cognitive dysfunction.
CONCLUSION: Our data suggest that unilateral combined stereotactic radiofrequency Pallidotomy and Thalamotomy for
idiopathic PD is an eective procedure.
KEYWORDS: Pallidotomy, Parkinson’s, Radiofrequency, Spasticity, Thalamotomy, Tremors.
Correspondence:
Mohamed Khaled Elkazaz
4.5 Km Ring Road, Suez Canal University Hospitals, Neurosurgery
Department 3rd oor, Ismailia, EGYPT
Email: Mohamed.elkazaz@med.suez.edu.eg
DOI: 10.21608/pajn.2023.204191.1090
Ali Salah Khedr,1 MD, PhD; Maha Abd El Fattah,2 MD, PhD; Mohamed Khaled Elkazaz,1 MD, PhD, MRCS
1Department of Neurosurgery, Faculty of Medicine, Suez Canal University, Ismailia, EGYPT
2Rheumatology and Physical Medicine Department, Faculty of Medicine, Suez Canal University, Ismailia, EGYPT
Received: 4 April 2023 / Accepted: 29 August 2023 / Published online: 18 December 2023
INTRODUCTION
Lesioning surgeries in Parkinson’s disease (PD) include
target obliteration of a certain area in brain tissue to disrupt
maladaptive neuronal arrangements. An advancement in
movement disorders occurred when stereotactic procedures
were applied in lesioning. Target selections were modulated
various times until in 1960s when Thalamotomy was used
for tremors and Pallidotomy was used for bradykinesia
and rigidity.1,2 Though lesioning procedures were executed
for numerous years in particular patients with PD, their
practice reduced in the 1960s following the presentation
of levodopa. However, long-term treatment with levodopa
has led to newly unfavorable side eects that refreshed the
era of lesioning surgeries.3
Lesioning procedures continued to develop, and currently
accessible methods include invasive procedures such
as thermoablation, radiofrequency and laser interstitial
thermal therapy (LITT), and less invasive procedures
such as magnetic resonance-guided high intensity
focused ultrasound (MRgFUS) ablation, and stereotactic
radiosurgery (SRS). Radiofrequency and thermaoablation
are the commonly used modalities.4,5
In 1954, Hassler and Reichert used thalamotomy to treat
tremors associated with PD. Ventrolateral thalamotomy
has been considered the neurosurgical treatment of choice
for disabling, drug-resistant parkinsonian and other types
of tremors. Tremors could be relieved not only by a
thalamic lesion but also by a lesion in the posteroventral
portion of the medial (Internal) Globus Pallidum (GPi)
and ventralis intermedius (VIM) nucleus of the Thalamus.
Hassler and Reichert proved that thalamotomy controls
the tremors related to PD.2 Various studies had shown
the role of VIM lesioning in control of PD medically
refractory tremors or other types of tremors.6–8
Unilateral Combined Stereotactic Radiofrequency Pallidotomy and Thalamotomy
for Idiopathic Parkinson’s Disease

Radiofrequency Pallidotomy and Thalamotomy for Parkinson’s Disease Khedr et al
140 PAN ARAB JOURNAL OF NEUROSURGERY
One of the studies retrospectively reviewed the results in
60 patients with PD tremors, cerebellar tremors, essential
tremors and post-traumatic tremors. All these patients
had unilateral VIM thalamotomy with mean follow-up
of 53.4 months. Patients with PD tremors had marked
improvement in 86% of the cases while patients with
essential tremors had similar improvement in 83% of
cases. Results were not as favorable for those patients
with post-traumatic tremors (50%) or cerebellar tremors
(67%). Temporary complications of thalamotomy were
seen in 60% of cases including dysarthria, dysphasia,
confusion, dystonia, contralateral paresis or sensory
disturbances.9
Lesion of the posteroventral segment of the internal
Globus Pallidus (GPi) is ecient at treating contralateral
tremor, rigidity, dyskinesia and bradykinesia.10 Various
studies supported this opinion. The rst of these studies
described an improvement in the o-state Unied
Parkinson’s Disease Rating Scale (UPDRS) motor score
of 65% at 1 year following the surgery.11 Lozano et al.
study showed UPDRS motor score improved in the o
state by 30% at 6 months postoperatively, although the
UPDRS akinesia score improved only by 33%. The gait
score showed 15% improvement in the o-state with
decrease in contralateral dyskinesias by 92%.12 Baron
et al. described a 25% improvement in the motor score
in the o state at 3 months postoperatively.13 Shannon
et al. described an improvement in 15% in the o-state
motor score 6 months postoperatively.14 This study aims
to evaluate the role of unilateral combined Thalamotomy
and Pallidotomy in improving the symptoms in patients
with PD.
PATIENTS AND METHODS
This prospective observational study included patients
suering from idiopathic Parkinson’s disease treated
at Suez Canal University between June 2017 and
December 2019. Total number of 62 patients underwent
stereotactic unilateral combined Pallidotomy “GPi” and
Thalamotomy “VIM” using radiofrequency ablation
for the management of Parkinson related tremors,
bradykinesia and rigidity, after careful counseling and
acquiring informed consent from the patients. All patients
have signed a consent for the publication purpose. This
article followed the world medical association declaration
of Helsinki ethical principles. The study was approved
by our institutional review board (IRB), and consent was
obtained from all patients.
We included only patients diagnosed with idiopathic
PD, with medication induced motor signs and refractory
tremors, and Hoehn and Yahr >2 o stage. Exclusion
criteria included multiple comorbidities that increase
morbidity and mortality risk of surgery, neuropsychiatric
diseases, dementia, postural instability and atypical PD
such as supranuclear gaze palsy, early postural instability
or severe early dysautonomia. We excluded patients who
failed to complete 24-months follow-up.
A multidisciplinary presurgical assessment was done by
neurosurgery and neurology team, including complete
physical and mental assessment of the patients presented
with PD. Neurology team was responsible for diagnosis
conrmation and assessment of the medication trials
the patients were oered. The o state was outlined
as the state after withdrawal of anti PD treatment by
12 hours, based on the Core Assessment Program for
Intracerebral Transplantations (CAPIT) committee
denition.15 The objective clinical test used in this study
was the UPDRS in o state motor assessment, tremors
and rigidity, both preoperatively and at 1, 6, 12 and 24
months postoperatively.16 Patients were also staged using
Hoehn and Yahr scale in o state preoperatively and
postoperatively at 1, 6, 12 and 24 months.17 Preoperative
imaging included magnetic resonance imaging (MRI)
and computed tomography (CT) brain one day prior to
surgery.
Operative details
After admission, patients were preoperatively assessed
by the anesthesia team. Stereotactic system Cosman-
Robert Wells (CRW) (Integra, NJ, USA) application was
performed under local anesthesia by scalp block. Patients
then underwent CT brain with the frame and ducials
applied to it. Data was analyzed and target selection was
done by waypoint navigator software (FHC, Bowdoin,
ME, USA), selecting the preferred points after fusion
between preoperative MRI, CT brain and post ducials
CT brain as follows.
Target selection
VIM target is 14 mm lateral and 6 mm anterior from
the posterior commissural point in the same anterior
commissure - posterior commissure (AC-PC) plane and
GPi point is 21 mm lateral and 3 mm anterior from the
mid commissural point at the mid-commissure (MC)
plane (Fig. 1). Specic adjustments were done in relation
to the lateral ventricular wall and internal capsule with
the fusion images. Afterwards, selected targets were
transferred to Stereocheck application (Mevis Informatica
Medica Ltda, Sao Paulo, Brazil) (Fig. 2), where both
entry and lesion targets were transformed into X, Y and
Z numbers. Preoperative placement of the patient on
the Mayeld (Integra, NJ, USA) was done. Patient was
connected with neurophysiological monitoring for motor
assessment. Sterile shaving and surgical draping was
done. Data gained from Stereocheck was then transferred
to phantom stereotaxis system and conrmed, then the
arc and ring was xed upon patients’ frame. Burr hole
guided by trajectory from the software was performed
followed by durotomy.

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Volume 18, No. 2, December 2023
Fig 2: Axial CT brain with ring and ducial marks for
planning in Stereocheck.
Fig 3: (A) Coronal and (B) axial CT brain showing thalamic
hematoma post-lesioning.
Electrode placement
The macroelectrode with bipolar 2-mm width, 3-mm
length and 3-mm tip was inserted through a guiding
tube with 2mm diameter, then it was connected to
the radiofrequency apparatus “Neuro N50” (Inomed,
Germany) with impedance monitoring until reaching
the target. Functional localization was done by
macrostimulation with 2 Hertz and 50 Hertz in both points
to assess proximity of the VIM target to ventral caudal
(VC) nucleus and internal capsule, and proximity of the
GPi target to the internal capsule. After conrmation
of the target, VIM underwent a temporarily lesioning
“50° C for 50 seconds” followed by careful assessment
of the patient. If there was no decit it was followed by
permanent lesion “65° C for 60 seconds” then withdrawal
by 2-mm and reapplying permanent lesion. GPi underwent
a temporarily lesioning “50° C for 50 seconds” followed
by careful assessment of the patient, then followed by
permanent lesion “72° C for 60 seconds”, withdrawal by
2-mm then reapplying permanent lesion. Hemostasis and
skin closure were done.
Postoperative assessment was done at 1, 6, 12 and 24
months for both the UPDRS o state and the Hoehn
and Yahr scale. Intraoperative and postoperative
complications were reported. Statistical analysis was
done using the statistical packages for the social sciences
(SPSS) version 26 (IOS, Chicago, IL, USA). Paired t-test
was implemented between means of variables.
RESULTS
Sixty-two patients were enrolled in the study; 37 males
and 25 females and the mean age was 57.47±9.90
years. Two patients failed to complete follow-up and
were excluded from the study. The average UPDRS
o motor assessment results showed marked reduction
after 1 month from 60.16 to 30.88. At 6-months and
1-year follow-up there was a non-signicant rise in
the average UPDRS o motor assessment to 39.1 and
42.3, respectively. At 24-months follow-up, the average
UPDRS o motor was 41.6. The average Hoehn and
Yahr scale was reduced from 3.63 to 1.19 after 1-month.
At 6-months and 12-months follow-up, there was a non-
signicant rise to 1.5 and 1.9, respectively. At 24 months
postoperatively, the average Hoehn and Yahr scale was
1.87 (Table 1) (Graphs 1,2).
Fig 1: A case of a 56 years old male patient with PD planning for right unilateral combined VIM and GPi lesioning. (A) Axial MRI
brain T1WI with VIM target “red crosshair right to third ventricle”. (B) Coronal MRI brain T1WI with VIM target “red crosshair
right to third ventricle”. (C) Axial MRI brain T1WI with GPi target “red crosshair right to third ventricle”. (D) Coronal MRI brain
T1WI with GPi target “red crosshair right to third ventricle”.

Radiofrequency Pallidotomy and Thalamotomy for Parkinson’s Disease Khedr et al
142 PAN ARAB JOURNAL OF NEUROSURGERY
The average UPDRS constancy of tremors (Graph 3)
was analyzed and showed a signicant improvement after
1-month duration from 3.53 to 0.75. There was a non-
signicant rise at 6 months and 12 months to 1.23 and
1.72, respectively. Total improvement in constancy of
tremors reached up to 75% of cases after 24-months with
average 1.62. In addition, the average UPDRS rigidity
score (Graph 4) also showed signicant improvement at
1-month follow-up from 3.31 to 1.21. There was a non-
signicant rise at 6 months and 12 months to 1.9 and
2.3, respectively. At 24-months follow-up, the average
reached 2.1. Total improvement of rigidity reached up to
63% of cases after 24-months.
Two patients (3.2%) had thalamic hematoma that was
discovered postoperatively with hemiplegia (Fig. 3). The
patients were managed conservatively, and they improved
after 1-month with little residual decit. Also noticed in
the study that 32 patients (51.6%) had gait imbalance
noticed at 6-months follow-up with leaning towards
the contralateral side to the lesioning. Fourteen patients
(22.5%) showed dysarthria immediately postoperative
and 8 of these patients (12.9%) totally recovered after
1-month. There were no recorded cases of infection, CSF
leaks or cognitive dysfunction.
Graph 1: UPDRS o motor state assessment.
Graph 2: Hoehn and Yahr assessment.

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Volume 18, No. 2, December 2023
Graph 3: UPDRS constancy of rest tremors assessment.
Graph 4: UPDRS rigidity assessment.
Table 1: Clinical assessment preoperatively and at the nal follow-up (After 24-months)
Item Preoperative (Mean±SD) 24-months (Mean±SD) T-score P-value
UPDRS o state motor score 60.16±3.8 41.6±4.49 10.23 <0.05*
Hoehn and Yahr scale 3.63±0.66 1.87±0.61 7.8 <0.05*
SD: standard deviation.
UPDRS: Unied Parkinson’s disease rating scale.
*p-value <0.05 is statistically signicant.

Radiofrequency Pallidotomy and Thalamotomy for Parkinson’s Disease Khedr et al
144 PAN ARAB JOURNAL OF NEUROSURGERY
DISCUSSION
Spiegel et al. in 1947 introduced the era of brain stereotactic
surgery.18 Later it became an evolution in this eld in the
management of PD. Hassler successfully managed to
control PD symptoms by Thalamotomy.19 Traditionally,
Thalamotomy alone was used as a maneuver for PD,
but after Leksell’s evolutionary introduction of the
GPi lesioning, rigidity and bradykinesia were managed
along with tremors.6 Long-term studies on isolated
Thalamotomies had shown that patients were still
disabled with rigidity. In addition studies which favored
that isolated lesion in GPi could control both rigidity and
tremors, was found later to be insucient to control the
tremors.20,21 VIM lesioning aims to disrupt the rubro-
thalamo-cortical circuit controlling abnormal impulses
initiating tremors,22,23 while GPi lesioning disconnect
the inhibitory outow of the GPi to the ventralis oralis
anterior (VOa) nucleus and the pedunculopontine
nucleus (PPN).22,24
In this series we had a success rate in improving patients
UPDRS and experiencing less relapse and complications.
Linhares et al. reported success of thalamotomy procedure
in suppressing tremors in PD with 75% improvement in
upper limb and 73% improvement in lower limb tremors.25
Fayed et al. reported successful results in combined
Pallidotomy and Thalamotomy over Pallidotomy alone
in improving patients functional state and controlling
PD.26 Several mechanisms were postulated regarding the
persistence of tremors after lesioning the GPi alone as
the GPi lesioning does not directly disconnect the rubro-
thalamo-cortical loop. In addition, it may exacerbate
the tremors by the disinhibition of the reticulospinal
system.23,27 Iacono et al. stated that combined VIM and
GPi lesioning could treat broad range of symptoms in PD
immediately with no or little risk on the patients.22
Study Limitations
The small sample size aected the statistical testing of
the results.
CONCLUSION
Unilateral combined VIM/GPi lesioning had shown to be
very eective in controlling PD symptoms and improving
the overall functional state of the patients. Despite being
a successful technique, few studies were focusing on it. It
showed to be potent and carries little risk for the patients.
We advocate that case-control studies should be directed
to assess this technique.
List of abbreviations
AC: Anterior commissure.
CAPIT: Core Assessment Program for Intracerebral.
Transplantations.
CRW: Cosman Roberts Wells.
CSF: Cerebrospinal uid.
CT: Computed tomography.
GPi: Globus pallidus internus.
IRB: Institutional review board.
LITT: Laser interstitial thermal therapy.
MC: Mid-commissure.
MRgFUS: Magnetic resonance -guided high intensity
focused ultrasound.
MRI: Magnetic resonance imaging.
PC: Posterior commissure.
PD: Parkinson’s disease.
PPN: Pedunculopontine nucleus.
SPSS: Statistical packages for the social sciences
SRS: Stereotactic radiosurgery.
UPDRS: Unied Parkinson’s Disease Rating Scale.
VC: Ventral caudal.
VIM: Ventralis intermedius.
VOa: Ventralis oralis anterior.
Disclosure
The authors report no conict of interest in the materials
or methods used in this study or the ndings specied in
this paper.
Funding
The authors received no nancial support for the research,
authorship, and/or publication of this paper.
Acknowledgements
Special thanks to the Neurosurgery Department in Suez
Canal University for the continuous support.
REFERENCES
1. Svennilson E, Torvik A, Lowe R, et al. Treatment
of parkinsonism by stereotactic thermolesions in the
pallidal region. A clinical evaluation of 81 cases.
Acta Psychiatr Scand. 1960;35(3):358-377.
2. Hassler R, Riechert T. Indications and localization
of stereotactic brain operations [Article in German].
Nervenarzt. 1954;25(11):441-447.
3. Marsden CD, Parkes JD. Success and problems of
long-term levodopa therapy in Parkinson’s disease.
Lancet. 1977;1(8007):345-349.
4. Walters H, Shah BB. Focused ultrasound and other
lesioning therapies in movement disorders. Curr
Neurol Neurosci Rep. 2019;19(9):66.
5. Jourdain VA, Schechtmann G. Health economics and
surgical treatment for Parkinson’s disease in a world
perspective: Results from an international survey.
Stereotact Funct Neurosurg. 2014;92(2):71-79.
6. Laitinen L V, Bergenheim AT, Hariz MI. Leksell’s
posteroventral pallidotomy in the treatment of
Parkinson’s disease. J Neurosurg. 1992;76(1):53-61.
7. Nagaseki Y, Shibazaki T, Hirai T, et al. Long-term
follow-up results of selective VIM-thalamotomy. J
Neurosurg. 1986;65(3):296-302.
8. Fox MW, Ahlskog JE, Kelly PJ. Stereotactic

Radiofrequency Pallidotomy and Thalamotomy for Parkinson’s Disease Khedr et al
145
Volume 18, No. 2, December 2023
ventrolateralis thalamotomy for medically refractory
tremor in post-levodopa era Parkinson’s disease
patients. J Neurosurg. 1991;75(5):723-730.
9. Jankovic J, Cardoso F, Grossman RG, et al. Outcome
after stereotactic thalamotomy for parkinsonian,
essential, and other types of tremor. Neurosurgery.
1995;37(4):680-687.
10. Lai EC, Jankovic J, Krauss JK, et al. Long-
term ecacy of posteroventral pallidotomy in
the treatment of Parkinson’s disease. Neurology.
2000;55(8):1218-1222.
11. Dogali M, Fazzini E, Kolodny E, et al. Stereotactic
ventral pallidotomy for Parkinson’s disease.
Neurology. 1995;45(4):753-761.
12. Lozano AM, Lang AE, Galvez-Jimenez N, et al.
Eect of GPi pallidotomy on motor function in
Parkinson’s disease. Lancet. 1995;346(8987):1383-
1387.
13. Baron MS, Vitek JL, Bakay RA, et al. Treatment
of advanced Parkinson’s disease by posterior GPi
pallidotomy: 1-year results of a pilot study. Ann
Neurol. 1996;40(3):355-366.
14. Shannon KM, Penn RD, Kroin JS, et al. Stereotactic
pallidotomy for the treatment of Parkinson’s disease:
Ecacy and adverse eects at 6 months in 26
patients. Neurology. 1998;50(2):434-438.
15. Langston JW, Widner H, Goetz CG, et al. Core
assessment program for intracerebral transplantations
(CAPIT). Mov Disord. 1992;7(1):2-13.
16. Movement Disorder Society Task Force on Rating
Scales for Parkinson’s Disease. The Unied
Parkinson’s Disease Rating Scale (UPDRS): Status
and recommendations. Mov Disord. 2003;18(7):738-
750.
17. Hoehn MM, Yahr MD. Parkinsonism: Onset,
progression, and mortality. 1967. Neurology.
1998;50(2):318-333.
18. Spiegel EA, Wycis HT, Marks M, et al. Stereotaxic
apparatus for operations on the human brain. Science.
1947;106(2754):349-350.
19. Hassler R. Extrapyramidal cortical systems and
central regulation of motor function [Article in
German]. Dtsch Z Nervenheilkd. 1956;175(3):233-
258.
20. Okun MS, Vitek JL. Lesion therapy for Parkinson’s
disease and other movement disorders: Update and
controversies. Mov Disord. 2004;19(4):375-389.
21. Taha JM, Favre J, Baumann TK, et al. Tremor control
after pallidotomy in patients with Parkinson’s
disease: Correlation with microrecording ndings. J
Neurosurg. 1997;86(4):642-647.
22. Iacono RP, Henderson JM, Lonser RR. Combined
stereotactic thalamotomy and posteroventral
pallidotomy for Parkinson’s disease. J Image Guid
Surg. 1995;1(3):133-140.
23. Narabayashi H. Neurophysiological ideas on
pallidotomy and ventrolateral thalamotomy for
hyperkinesis. Conn Neurol. 1962;22:291-303.
24. Ohye C. Depth microelectrode studies. In:
Schaltenbrand G, Walker AE, eds. Stereotaxy of
the Human Brain: Anatomical, Physiological and
Clinical Applications. 2nd ed. Thieme. 1982:510–514.
25. Linhares MN, Tasker RR. Microelectrode-guided
thalamotomy for Parkinson’s disease. Neurosurgery.
2000;46(2):390-398.
26. Fayed ZY, Radwan H, Aziz M, et al. Combined
unilateral posteroventral pallidotomy and ventral
intermediate nucleus thalamotomy in tremor-
dominant Parkinson’s disease versus posteroventral
pallidotomy alone: A prospective comparative study.
Stereotact Funct Neurosurg. 2018;96(4):264-269.
27. Sandyk R, Iacono RP. The relationship of the reticular
system to the primary pathoetiology of Parkinson’s
disease. Int J Neurosci. 1988;42(3-4):297-300.