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DOI: 10.1055/s-0045-1811973
Fastigial Point as Deep Brain Stimulation Repair
Ponto fastigial como reparo de estimulação cerebral profundaAuthors
Abstract
Objective
To establish anatomical and functional criteria, based on stereotactic imaging and electrophysiological recordings, which enable the precise implantation of electrodes in the dentate nucleus and its projections for the treatment of movement disorders.
Materials and Methods
Ten patients with movement disorders or cerebellar abnormalities underwent bilateral deep brain stimulation (DBS) of the dentate nucleus (DN). The initial targets were defined using coordinates based on the fastigial point (FP); then, the target was refined through direct visualization of the DN using susceptibility weighted imaging (SWI) and T2-weighted magnetic resonance imaging (MRI) sequences and further adjusted based on reconstruction of the dentato-rubro-thalamic tract (DRTT).
Results
The ventral portion of the DN and the estimated vicinity of the DRTT were established as the target region, with the distal electrode contact positioned in the white matter and the proximal contacts within the DN. The coordinates were refined using direct imaging of the DN on SWI and T2 sequences, fused with stereotomography and contrast-enhanced volumetric T1 MRI. The electrode trajectory was adjusted to remain within the DN, as parallel and close as possible to the DRTT fibers. Surgical planning also defined the entry points and intracranial trajectories of the instruments, ensuring a safe path from the suboccipital bone to the targets, while avoiding venous sinuses and vessels visualized on contrast-enhanced images.
Conclusion
Precise localization of the DN based on DRTT tractography proved feasible using currently available stereotactic and imaging processing resources. The technique described enables coregistration of computed tomography (CT), MRI, and tractography images, representing a simple, safe, and effective methodology for performing DBS of the DN.
Resumo
Objetivo
Estabelecer critérios anatômicos e funcionais, baseados em imagens estereotáxicas e registros eletrofisiológicos, que permitam a implantação precisa de eletrodos no núcleo denteado e em suas projeções para o tratamento de distúrbios do movimento.
Materiais e Métodos
Dez pacientes com distúrbios do movimento ou anormalidades cerebelares foram submetidos à estimulação cerebral profunda (ECP) bilateral do núcleo denteado (ND). Os alvos iniciais foram definidos utilizando coordenadas baseadas no ponto fastigial (PF) e, em seguida, refinados por meio da visualização direta do ND em sequências de imagem ponderada por suscetibilidade (SWI) e ressonância magnética (RM) ponderada em T2, sendo posteriormente ajustados com base na reconstrução do trato dento-rubro-talâmico (TTD).
Resultados
A porção ventral do ND e a vizinhança estimada do TTD foram estabelecidas como a região alvo, com o contato distal do eletrodo posicionado na substância branca e os contatos proximais dentro do ND. As coordenadas foram refinadas utilizando imagens diretas do ND em sequências SWI e T2, combinadas com estereotomografia e RM volumétrica em T1 com contraste. A trajetória do eletrodo foi ajustada para permanecer dentro do ND, o mais paralela e próxima possível das fibras do TTRD. O planejamento cirúrgico também definiu os pontos de entrada e as trajetórias intracranianas dos instrumentos, garantindo um caminho seguro do osso suboccipital até os alvos e evitando seios venosos e vasos visualizados em imagens com contraste.
Conclusão
A localização precisa do ND com base na tractografia do TTRD mostrou-se viável utilizando os recursos de processamento de imagem e estereotáxico atualmente disponíveis. A técnica descrita permite o corregistro de imagens de tomografia computadorizada (TC), ressonância magnética e tractografia, representando uma metodologia simples, segura e eficaz para a realização de ECP do ND.
Keywords
nucleus dentatus - cerebellar nuclei - dystonia ataxia transcranial direct current stimulation - deep brain stimulationPalavras-chave
núcleo dentatus - núcleos cerebelares - distonia ataxia estimulação transcraniana corrente contínua - estimulação cerebral profundaIntroduction
Movement abnormalities, such as spasticity, athetosis, ataxia, and dystonia, represent relevant clinical challenges, often refractory to conventional pharmacological and physiotherapeutic approaches. Patients with cerebral palsy or brain injuries acquired early require therapeutic alternatives that promote symptomatic relief without additional impairment of neurological functions.
Among the neurosurgical options, ablative lesions in deep structures (such as thalamotomy and pallidotomy) and deep brain stimulation (DBS) of the thalamic nuclei and globus pallidus stand out. Although effective in some cases, these techniques have limited and inconsistent results in the sustained modulation of spasticity, especially in diffuse cases and those associated with non-progressive encephalopathies. Such variability is partly due to the heterogeneity of neurosurgical targets, imprecision in the location of lesions, and inadequate patient selection.
In this context, cerebellar dentatotomy—an intervention that aims to modulate the activity of the dentate nucleus (DN)—emerges as a promising alternative, although still little explored. Unlike traditional subcortical approaches, the manipulation of the DN seeks to modulate cerebellocortical circuits, which are known to be involved in the regulation of motor skills.
The DN, the largest deep cerebellar nucleus, constitutes the main efferent pathway of the cerebellar hemispheres, influencing cortical motor areas through connections with the ventrolateral nucleus of the thalamus. Evidence suggests that selective modulation of the DN can reduce ipsilateral spasticity and, in some cases, improve proximal involuntary movements, although its effectiveness depends on the pathophysiology and location of the brain injury.
Advances in neuroimaging, such as high-resolution magnetic resonance imaging (MRI) and coregistration with computed tomography, have allowed greater precision in the identification of DN, enabling safer and more effective interventions. However, the absence of objective and standardized criteria for the localization and modulation of DN still limits reproducibility and optimization of clinical outcomes.
In view of this scenario, the present work proposes an integrated approach to determine stereotactic repairs and electrographic patterns of the DN, aiming at the safe implantation of electrodes for electrical stimulation in the treatment of movement abnormalities. The central objective is to establish objective criteria for the localization and modulation of the DN, describing the potential therapeutic and adverse effects of its selective stimulation or injury, based on robust neuroanatomical and neurophysiological evidence.
Thus, the present study seeks to contribute to the improvement of cerebellar interventions in the treatment of spasticity and other movement disorders, strengthening the role of DN as a therapeutic target in functional neurosurgery.
Materials and Methods
Study Design
An observational, descriptive and retrospective study was performed with the objective of determining and validating anatomical and electrophysiological parameters for the implantation of DBS electrodes in the DN and their projections. Data from the medical records of patients who underwent the procedure were analyzed, correlating the preoperative planning with the final stereotactic coordinates of the implanted electrodes.
Ethical Aspects
The study was conducted at the Pain Center, Department of Neurology, Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo (HCFMUSP), between September 2016 and December 2020. The protocol was approved by the Research Ethics Committee (CAAE: 32779514.5.0000.0068; Opinion: 2.428.661).
Study Population
Ten adult patients (≥ 18 years old) with severe spasticity secondary to encephalopathies of various etiologies (cerebral palsy, traumatic brain injury, sequelae of stroke), refractory to conventional clinical and physical therapy treatment, and with formal indication for DN DBS, were included. All patients had complete medical record, technical success in the implantation, and a minimum clinical follow-up of 6 months. Patients under 18 years of age, incomplete medical records, technical failure in the implant, or complications that prevented the activation of the system were excluded.
Study Sample
The sample consisted of 7 men and 3 women, aged between 29 and 74 years. The etiologies included cerebellar vascular injury (n = 2), spinocerebellar ataxia type 3 (n = 5), sequelae of tumor resection in the posterior fossa (n = 1), and traumatic brain injury (n = 2), totaling 20 implanted electrodes.
Preoperative Planning and Stereotactic
Surgical planning integrated high-resolution neuroimaging (1.5T MRI, 1 mm slices, susceptibility weighted imaging [SWI], T1, T2, and diffusion tensor imaging [DTI] sequences for tractography) and computed tomography (CT) of the head (1 mm). The images were fused and co-recorded (MNPS software; Mevis Informática Médica LTDA.), allowing the precise definition of the targets in the DN and in the dentato-rubro-thalamic tract (DRTT) projections. Stereotactic coordinates were calculated based on established anatomical references (anterior and posterior commissures, interhemispheric midline, fastigial point), using the Schaltenbrand-Ahren atlas.
Surgical Protocol
The procedures were performed under general anesthesia, with the patient in the prone position and fixation of the ETM-3 stereotactic system (Elekta). After antibiotic prophylaxis and aseptic preparation, bilateral trepanning was performed on the occipital scale, guided by the planned coordinates. The surgical approach followed the standard technique, with local infiltration, hemostasis, and exposure of the occipital bone.
Micro-registration and Intraoperative Stimulation
A cannula and micro-registration electrodes (Inomed) were used for millimetric electrophysiological recording of cerebellar neuronal activity, with electrical stimuli of 30 Hz and 1 mA, from 10 mm proximal to the target to 5 mm beyond the DN. The objective was to identify safe paths and confirm the functional location of the DN and the TRD.
Implantation and Connection of Electrodes
After electrophysiological confirmation, quadripolar electrodes (Abbott) were definitively implanted in the DN and DRTT, with bone fixation and subcutaneous tunneling for connection to the Libra XP pulse generator (Abbott) in the prepectoral pocket. The position of the electrodes was confirmed by intraoperative radioscopy and postoperative CT. The impedances of the contacts were measured by telemetry.
Postoperative Evaluation and Programming
In the immediate postoperative period, all patients underwent a follow-up CT scan and were discharged without intercurrences. The initial activation and programming of the generators occurred three weeks after surgery, on an outpatient basis, with detailed neurological evaluation and progressive adjustment of the stimulation parameters. The monopolar patch test was performed systematically, followed by a bipolar configuration according to clinical response. Patients were followed up weekly for the first eight weeks for individualized adjustments.
Data Analysis
The three-dimensional coordinates (X, Y, Z) of the DN and DRTT were converted to numerical format, and the Euclidean distance to the fastigial point (FP) was calculated. A mixed linear regression model was applied to estimate the mean position of the structures, incorporating random intercept per patient to control individual anatomical variability. Estimates and confidence intervals were extracted and presented in tables. Interactive three-dimensional graphs (plotly) were generated for spatial visualization of the data.
All processing was performed in RStudio (Posit) version 4.3.3, using the readxl, tidyverse, lme4, gtsummary, flextable, officer, plotly, and htmlwidgets packages.
Results
We included 10 patients who underwent bilateral DBS of the DN, with a mean age of 52.2 (range: 29–74) years, with a predominance of spinocerebellar ataxia type 3 (60%), followed by cerebellar vascular injury (20%) and brain injury (20%).
The analysis of the stereotactic coordinates revealed that the location of the DN and DRTT could be accurately performed by means of the coregistration of MRI and CT images, complemented by intraoperative electrophysiological recordings. The means and standard deviations of the stereotactic coordinates of the targets (DN and DRTT) showed greater variability in the anteroposterior dimension of DRTT, especially between hemispheres of the same patient, suggesting the influence of the etiology of the disease on the local anatomy. No significant differences were observed between genders.
The angles of introduction of the electrodes varied according to the planned trajectory but remained within safe margins, with the trepanation point consistently positioned caudal to the transverse sinus, minimizing vascular risks.
The fastigial point (FP) proved to be a stable and easily identifiable anatomical repair in all imaging studies, with no significant variation between patients, reinforcing its usefulness as a reference for stereotactic planning of DN and DRTT.
In summary, the spatial variability observed, especially in DRTT, highlights the need for individualization of surgical planning, using reliable anatomical repairs and advanced imaging techniques to optimize electrode positioning and clinical outcomes.
Discussion
Deep brain stimulation of cerebellar structures, especially the DN and the DRTT, has re-emerged as a promising alternative for the treatment of refractory movement disorders, driven by advances in neuroimaging, stereotactic, and neuromodulation technology. The present study reinforces the feasibility and accuracy of DN and DRTT targeting through coregistration of MRI and CT images, complemented by tractography and robust anatomical repairs, such as the FP.
Historically, the location of the DN in ablative or DBS procedures has depended on stereotactic atlases, with significant interindividual variability. The integration of advanced imaging techniques, especially DTI tractography, allows for the individualization of surgical planning, optimizing the positioning of the electrodes and enhancing clinical outcomes. Our findings demonstrate that the FP is a stable and reproducible anatomical repair, facilitating the localization of the DN and DRTT, even in scenarios with technological limitations.
The variability observed in stereotactic coordinates, especially in DRTT, highlights the influence of etiology and individual anatomy, reinforcing the need for personalized planning. Recent literature corroborates that the proximity of active electrode contacts to DRTT is associated with better clinical outcomes, especially in the control of tremors, dystonia, and spasticity.
Among the limitations of the present study, the limited number of cases and the resolution of deterministic tractography stand out. Even so, the proposed standardization for the use of the FP as an anatomical reference contributes to greater precision and reproducibility in the implantation of cerebellar electrodes.
In summary, this study proposes a systematized and reproducible approach to the targeting of DN and DRTT, based on reliable anatomical repairs and advanced imaging techniques. The use of the FP as a reference can expand access to cerebellar interventions, even in resource-limited settings, and serve as a basis for future clinical and translational studies in neuromodulation of movement disorders.
Conclusion
The current study demonstrates that DN and the DRTT are relevant neurosurgical targets for the modulation of refractory movement disorders, especially in cases of spasticity. The integrated use of advanced neuroimaging and electrophysiological recording techniques allowed the individualization and optimization of electrode positioning, overcoming the limitations of traditional methods based only on anatomical atlases.
The main contribution of this work is the validation of the FP as a stable and reliable anatomical repair for the stereotactic planning of the DN and DRTT, facilitating safe and reproducible interventions, even in resource-limited settings. The proposed approach expands the precision and accessibility of cerebellar neuromodulation, with the potential to improve clinical outcomes and expand therapeutic indications.
In summary, the standardization of the use of the FP as an anatomical reference represents a significant advance for functional neurosurgery, consolidating the DN and DRTT as strategic targets in the rehabilitation of patients with difficult-to-manage movement disorders.
No conflict of interest has been declared by the author(s).
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Publication History
Received: 05 August 2025
Accepted: 07 August 2025
Article published online:
08 October 2025
© 2025. Sociedade Brasileira de Neurocirurgia. This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/)
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