Search Results

You are looking at 1 - 10 of 18 items for

  • Author or Editor: Mojgan Hodaie x
  • All content x
Clear All Modify Search
Restricted access

Peter Shih-Ping Hung, Sarasa Tohyama, Jia Y. Zhang, and Mojgan Hodaie

OBJECTIVE

Gamma Knife radiosurgery (GKRS) is a noninvasive surgical treatment option for patients with medically refractive classic trigeminal neuralgia (TN). The long-term microstructural consequences of radiosurgery and their association with pain relief remain unclear. To better understand this topic, the authors used diffusion tensor imaging (DTI) to characterize the effects of GKRS on trigeminal nerve microstructure over multiple posttreatment time points.

METHODS

Ninety-two sets of 3-T anatomical and diffusion-weighted MR images from 55 patients with TN treated by GKRS were divided within 6-, 12-, and 24-month posttreatment time points into responder and nonresponder subgroups (≥ 75% and < 75% reduction in posttreatment pain intensity, respectively). Within each subgroup, posttreatment pain intensity was then assessed against pretreatment levels and followed by DTI metric analyses, contrasting treated and contralateral control nerves to identify specific biomarkers of successful pain relief.

RESULTS

GKRS resulted in successful pain relief that was accompanied by asynchronous reductions in fractional anisotropy (FA), which maximized 24 months after treatment. While GKRS responders demonstrated significantly reduced FA within the radiosurgery target 12 and 24 months posttreatment (p < 0.05 and p < 0.01, respectively), nonresponders had statistically indistinguishable DTI metrics between nerve types at each time point.

CONCLUSIONS

Ultimately, this study serves as the first step toward an improved understanding of the long-term microstructural effect of radiosurgery on TN. Given that FA reductions remained specific to responders and were absent in nonresponders up to 24 months posttreatment, FA changes have the potential of serving as temporally consistent biomarkers of optimal pain relief following radiosurgical treatment for classic TN.

Full access

Sarasa Tohyama, Peter Shih-Ping Hung, Jidan Zhong, and Mojgan Hodaie

OBJECTIVE

Gamma Knife radiosurgery (GKRS) is an important treatment modality for trigeminal neuralgia (TN). Current longitudinal assessment after GKRS relies primarily on clinical diagnostic measures, which are highly limited in the prediction of long-term clinical benefit. An objective, noninvasive, predictive tool would be of great utility to advance the clinical management of patients. Using diffusion tensor imaging (DTI), the authors’ aim was to determine whether early (6 months post-GKRS) target diffusivity metrics can be used to prognosticate long-term pain relief in patients with TN.

METHODS

Thirty-seven patients with TN treated with GKRS underwent 3T MRI scans at 6 months posttreatment. Diffusivity metrics of fractional anisotropy, axial diffusivity, radial diffusivity, and mean diffusivity were extracted bilaterally from the radiosurgical target of the affected trigeminal nerve and its contralateral, unaffected nerve. Early (6 months post-GKRS) diffusivity metrics were compared with long-term clinical outcome. Patients were identified as long-term responders if they achieved at least 75% reduction in preoperative pain for 12 months or longer following GKRS.

RESULTS

Trigeminal nerve diffusivity at 6 months post-GKRS was predictive of long-term clinical effectiveness, where long-term responders (n = 19) showed significantly lower fractional anisotropy at the radiosurgical target of their affected nerve compared to their contralateral, unaffected nerve and to nonresponders. Radial diffusivity and mean diffusivity, correlates of myelin alterations and inflammation, were also significantly higher in the affected nerve of long-term responders compared to their unaffected nerve. Nonresponders (n = 18) did not exhibit any characteristic diffusivity changes after GKRS.

CONCLUSIONS

The authors demonstrate that early postsurgical target diffusivity metrics have a translational, clinical value and permit prediction of long-term pain relief in patients with TN treated with GKRS. Importantly, an association was found between the footprint of radiation and clinical effectiveness, where a sufficient level of microstructural change at the radiosurgical target is necessary for long-lasting pain relief. DTI can provide prognostic information that supplements clinical measures, and thus may better guide the postoperative assessment and clinical decision-making for patients with TN.

Free access

Vibhor Krishna, Francesco Sammartino, Philip Yee, David Mikulis, Matthew Walker, Gavin Elias, and Mojgan Hodaie

OBJECTIVE

The diagnosis of Chiari malformation Type I (CM-I) is primarily based on the degree of cerebellar tonsillar herniation even though it does not always correlate with symptoms. Neurological dysfunction in CM-I presumably results from brainstem compression. With the premise that conventional MRI does not reveal brain microstructural changes, this study examined both structural and microstructural neuroimaging metrics to distinguish patients with CM-I from age- and sex-matched healthy control subjects.

METHODS

Eight patients with CM-I and 16 controls were analyzed. Image postprocessing involved coregistration of anatomical T1-weighted with diffusion tensor images using 3D Slicer software. The structural parameters included volumes of the posterior fossa, fourth ventricle, and tentorial angle. Fractional anisotropy (FA) was calculated separately in the anterior and posterior compartments of the lower brainstem.

RESULTS

The mean age of patients in the CM-I cohort was 42.6 ± 10.4 years with mean tonsillar herniation of 12 mm (SD 0.7 mm). There were no significant differences in the posterior fossa volume (p = 0.06) or fourth ventricular volume between the 2 groups (p = 0.11). However, the FA in the anterior brainstem compartment was significantly higher in patients with CM-I preoperatively (p = 0.001). The FA values normalized after Chiari decompression except for persistently elevated FA in the posterior brainstem compartment in patients with CM-I and syrinx.

CONCLUSIONS

In this case-control study, microstructural alterations appear to be reliably associated with the diagnosis of CM-I, with a significantly elevated FA in the lower brainstem in patients with CM-I compared with controls. More importantly, the FA values normalized after decompressive surgery. These findings should be validated in future studies to determine the significance of diffusion tensor imaging–based assessment of brainstem microstructural integrity as an adjunct to the clinical assessment in patients with CM-I.

Free access

Joao Paulo Almeida, Carlos Velásquez, Claire Karekezi, Miguel Marigil, Mojgan Hodaie, James T. Rutka, and Mark Bernstein

OBJECTIVE

International collaborations between high-income (HICs) and low- and middle-income countries (LMICs) have been developed as an attempt to reduce the inequalities in surgical care around the world. In this paper the authors review different models for international surgical education and describe projects developed by the Division of Neurosurgery at the University of Toronto in this field.

METHODS

The authors conducted a review of models of international surgical education reported in the literature in the last 15 years. Previous publications on global neurosurgery reported by the Division of Neurosurgery at the University of Toronto were reviewed to exemplify the applications and challenges of international surgical collaborations.

RESULTS

The most common models for international surgical education and collaboration include international surgical missions, long-term international partnerships, fellowship training models, and online surgical education. Development of such collaborations involves different challenges, including limited time availability, scarce funding/resources, sociocultural barriers, ethical challenges, and lack of organizational support. Of note, evaluation of outcomes of international surgical projects remains limited, and the development and application of assessment tools, such as the recently proposed Framework for the Assessment of International Surgical Success (FAIRNeSS), is encouraged.

CONCLUSIONS

Actions to reduce inequality in surgical care should be implemented around the world. Different models can be used for bilateral exchange of knowledge and improvement of surgical care delivery in regions where there is poor access to surgical care. Implementation of global neurosurgery initiatives faces multiple limitations that can be ameliorated if systematic changes occur, such as the development of academic positions in global surgery, careful selection of participant centers, governmental and nongovernmental financial support, and routine application of outcome evaluation for international surgical collaborations.

Restricted access

Myriam Lafreniere-Roula, William D. Hutchison, Andres M. Lozano, Mojgan Hodaie, and Jonathan O. Dostrovsky

Object

The aim of the current study was to examine and compare the aftereffects of local high-frequency microstimulation through the recording electrode on the firing of neurons in the subthalamic nucleus (STN) and the substantia nigra pars reticulata (SNr) in patients undergoing surgery for deep brain stimulation. Deep brain stimulation has been playing an increasing role in the treatment of Parkinson disease, with the subthalamic nucleus (STN) being the preferred implantation target. Changes in cellular activity indicative of the borders of the STN are typically used during surgery to determine the extent of the STN and locate the optimal target, but in some cases borders may be difficult to identify. In this study the authors compared the effects of microstimulation in the SNr and STN. In previous studies they have shown that microstimulation in the internal globus pallidus, which is functionally similar to the SNr, inhibits firing, whereas similar microstimulation in the STN has minimal effect. The presence of inhibition in the SNr but not in the STN could be used as an additional criterion to help identify the location of the border between the STN and SNr.

Methods

Dual microelectrode recordings were performed during stereotactic surgery in 4 patients. Well-isolated high-amplitude units were stimulated extracellularly through the recording microelectrode with 0.5-second trains of high frequency (200 Hz) and low current (≤ 5 μA).

Results

In the majority (92%) of SNr neurons, this type of stimulation led to a period of inhibition lasting several hundreds of milliseconds following the end of the train. In contrast, only 1 neuron of 70 judged to be in the STN by other criteria was inhibited by this type of microstimulation, and this neuron was located at the ventral border of the STN.

Conclusions

These findings indicate that prolonged inhibition of firing following low-amplitude high-frequency microstimulation via the recording electrode is a consistent feature of almost all SNr neurons and rarely if ever occurs in STN neurons. This feature therefore provides a useful additional finding that can be used to help identify the border between the STN and SNr.

Full access

Francesco Sammartino, Vibhor Krishna, Tejas Sankar, Jason Fisico, Suneil K. Kalia, Mojgan Hodaie, Walter Kucharczyk, David J. Mikulis, Adrian Crawley, and Andres M. Lozano

OBJECTIVE

The aim of this study was to evaluate the safety of 3-T MRI in patients with implanted deep brain stimulation (DBS) systems.

METHODS

This study was performed in 2 phases. In an initial phantom study, a Lucite phantom filled with tissue-mimicking gel was assembled. The system was equipped with a single DBS electrode connected to an internal pulse generator. The tip of the electrode was coupled to a fiber optic thermometer with a temperature resolution of 0.1°C. Both anatomical (T1- and T2-weighted) and functional MRI sequences were tested. A temperature change within 2°C from baseline was considered safe. After findings from the phantom study suggested safety, 10 patients with implanted DBS systems targeting various brain areas provided informed consent and underwent 3-T MRI using the same imaging sequences. Detailed neurological evaluations and internal pulse generator interrogations were performed before and after imaging.

RESULTS

During phantom testing, the maximum temperature increase was registered using the T2-weighted sequence. The maximal temperature changes at the tip of the DBS electrode were < 1°C for all sequences tested. In all patients, adequate images were obtained with structural imaging, although a significant artifact from lead connectors interfered with functional imaging quality. No heating, warmth, or adverse neurological effects were observed.

CONCLUSIONS

To the authors' knowledge, this was the first study to assess the clinical safety of 3-T MRI in patients with a fully implanted DBS system (electrodes, extensions, and pulse generator). It provided preliminary data that will allow further examination and assessment of the safety of 3-T imaging studies in patients with implanted DBS systems. The authors cannot advocate widespread use of this type of imaging in patients with DBS implants until more safety data are obtained.

Free access

Catherine Veilleux, Nardin Samuel, Han Yan, Victoria Bass, Rabab Al-Shahrani, Ann Mansur, James T. Rutka, Gelareh Zadeh, Mojgan Hodaie, and Geneviève Milot

OBJECTIVE

Although the past decades have seen a steady increase of women in medicine in general, women continue to represent a minority of the physician-training staff and workforce in neurosurgery in Canada and worldwide. As such, the aim of this study was to analyze the experiences of women faculty practicing neurosurgery across Canada to better understand and address the factors contributing to this disparity.

METHODS

A historical, cross-sectional, and mixed-method analysis of survey responses was performed using survey results obtained from women attending neurosurgeons across Canada. A web-based survey platform was utilized to collect responses. Quantitative analyses were performed on the responses from the study questionnaire, including summary and comparative statistics. Qualitative analyses of free-text responses were performed using axial and open coding.

RESULTS

A total of 19 of 31 respondents (61.3%) completed the survey. Positive enabling factors for career success included supportive colleagues and work environment (52.6%); academic accomplishments, including publications and advanced degrees (36.8%); and advanced fellowship training (47.4%). Perceived barriers reported included inequalities with regard to career advancement opportunities (57.8%), conflicting professional and personal interests (57.8%), and lack of mentorship (36.8%). Quantitative analyses demonstrated emerging themes of an increased need for women mentors as well as support and recognition of the contributions to career advancement of personal and family-related factors.

CONCLUSIONS

This study represents, to the authors’ knowledge, the first analysis of factors influencing career success and satisfaction in women neurosurgeons across Canada. This study highlights several key factors contributing to the low representation of women in neurosurgery and identifies specific actionable items that can be addressed by training programs and institutions. In particular, female mentorship, opportunities for career advancement, and increased recognition and integration of personal and professional roles were highlighted as areas for future intervention. These findings will provide a framework for addressing these factors and improving the recruitment and retention of females in this specialty.

Full access

Nicolas Kon Kam King, Vibhor Krishna, Diellor Basha, Gavin Elias, Francesco Sammartino, Mojgan Hodaie, Andres M. Lozano, and William D. Hutchison

OBJECTIVE

The ventral intermediate nucleus (VIM) of the thalamus is not visible on structural MRI. Therefore, direct VIM targeting methods for stereotactic tremor surgery are desirable. The authors previously described a direct targeting method for visualizing the VIM and its structural connectivity using deterministic tractography. In this combined electrophysiology and imaging study, the authors investigated the electrophysiology within this tractography-defined VIM (T-VIM).

METHODS

Thalamic neurons were classified based on their relative location to the T-VIM: dorsal, within, and ventral to the T-VIM. The authors identified the movement-responsive cells (kinesthetic and tremor cells), performed spike analysis (firing rate and burst index), and local field potential analysis (area under the curve for 13–30 Hz). Tremor efficacy in response to microstimulation along the electrode trajectory was also assessed in relation to the T-VIM.

RESULTS

Seventy-three cells from a total of 9 microelectrode tracks were included for this analysis. Movement-responsive cells (20 kinesthetic cells and 26 tremor cells) were identified throughout the electrode trajectories. The mean firing rate and burst index of cells (n = 27) within the T-VIM are 18.8 ± 9.8 Hz and 4.5 ± 5.4, respectively. Significant local field potential beta power was identified within the T-VIM (area under the curve for 13–30 Hz = 6.6 ± 7.7) with a trend toward higher beta power in the dorsal T-VIM. The most significant reduction in tremor was also observed in the dorsal T-VIM.

CONCLUSIONS

The electrophysiological findings within the VIM thalamus defined by tractography, or T-VIM, correspond with the known microelectrode recording characteristics of the VIM in patients with tremor.

Open access

Nebras M. Warsi, Ann Wilson, Armaan K. Malhotra, Jerry C. Ku, Ahmed A. Najjar, Esther Bui, Michael Baker, Eric Bartlett, and Mojgan Hodaie

BACKGROUND

The purpose of the present case report is to highlight the presentation, workup, clinical decision making, and operative intervention for a 68-year-old woman who developed rapidly progressive myelopathy secondary to idiopathic cervical intramedullary abscess.

OBSERVATIONS

The patient underwent laminectomy and aspiration/biopsy of the lesion. Intraoperatively, division of the posterior median sulcus released a large volume of purulent material growing the oral pathogens Eikenella corrodens and Gemella morbillorum. Broad-spectrum antibiotics were initiated postoperatively. At the 6-month follow-up, the patient had almost completely recovered with some persistent hand dysesthesia. Complete infectious workup, including full dental assessment and an echocardiogram, failed to reveal the source of her infection.

LESSONS

The authors report the first case of cryptogenic spinal intramedullary abscess secondary to Eikenella spp. and Gemella spp. coinfection. Intramedullary abscesses are exceptionally rare and most commonly develop in children with dermal sinus malformations or in the context of immunosuppression. In adults without risk factors, they can readily be mistaken for more common pathologies in this age group, such as intramedullary neoplasms or demyelinating disease. Prompt diagnosis and management based on rapidly progressive myelopathy, assessment of infectious risk factors and/or symptoms, and targeted imaging are critical to avoid potentially devastating neurological sequelae.