Andrew Parrent - Academia.edu (original) (raw)

Papers by Andrew Parrent

Clinical Neurology and Neurosurgery, Jul 1, 2014

Neurosurgery, May 1, 2020

Journal of Neurosurgery, Mar 1, 2022

Survey of Anesthesiology, Aug 1, 1998

Canadian Journal of Neurological Sciences, May 1, 2000

Neuromodulation: Technology at the Neural Interface

Neuromodulation: Technology at the Neural Interface, 2020

Stimulation of the dorsal spinal roots, or spinal nerve root stimulation (SNRS), is a neuromodula... more Stimulation of the dorsal spinal roots, or spinal nerve root stimulation (SNRS), is a neuromodulation modality that can target pain within specific dermatomal distributions. The use of paresthesia‐free stimulation has been described with conventional dorsal column spinal cord stimulation, although has yet to be described for SNRS. This objective of this study was to investigate the efficacy of paresthesia‐free high‐frequency (1000–1200 Hz) SNRS in the treatment of intractable, dermatomal neuropathic pain.

Journal of Neurosurgery, 2021

OBJECTIVE Epilepsy surgery for older adults is controversial owing to their longer duration of ep... more OBJECTIVE Epilepsy surgery for older adults is controversial owing to their longer duration of epilepsy and perceived higher surgical risk. However, because of an aging population and documented benefit of epilepsy surgery, surgery is considered more frequently for these patients. The authors’ objective was to analyze the role of resective surgery in patients older than 60 years and to assess outcomes and safety. METHODS The authors conducted a retrospective analysis of 595 patients who underwent resective epilepsy surgery at their center from 1999 to 2018. Thirty-one patients aged 60 years or older were identified. Sixty patients younger than 60 years were randomly selected as controls. Population characteristics, results of presurgical evaluations, outcomes, and complications were analyzed. RESULTS No significant differences were found between the groups in terms of hemisphere dominance, side of surgery, presence of a lesion, and incidence of temporal lobe epilepsy. Epilepsy durat...

Computer aided surgery : official journal of the International Society for Computer Aided Surgery, 2006

We present the development of a visualization and navigation system and its application in pre-op... more We present the development of a visualization and navigation system and its application in pre-operative planning and intra-operative guidance of stereotactic deep-brain neurosurgical procedures for the treatment of Parkinson's disease, chronic pain, and essential tremor. This system incorporates a variety of standardized functional and anatomical information, and is capable of non-rigid registration, interactive manipulation, and processing of clinical image data. The integration of a digitized and segmented brain atlas, an electrophysiological database, and collections of final surgical targets from previous patients facilitates the delineation of surgical targets and surrounding structures, as well as functional borders. We conducted studies to compare the surgical target locations identified by an experienced stereotactic neurosurgeon using multiple electrophysiological exploratory trajectories with those located by a non-expert using this system on 70 thalamotomy, pallidoto...

Canadian Journal of Neurological Sciences / Journal Canadien des Sciences Neurologiques, 2020

ABSTRACT:Objective:To describe the experience with Anterior Nucleus of the Thalamus-Deep Brain St... more ABSTRACT:Objective:To describe the experience with Anterior Nucleus of the Thalamus-Deep Brain Stimulation (ANT-DBS) for the treatment of epilepsy at a Canadian Center.Methods:All patients who underwent ANT-DBS implantation between 2013 (first patient implanted at our center) and 2020 were included. These patients had therapy-resistant epilepsy (TRE), were not candidates for resective surgery, and failed vagus nerve stimulation (VNS) treatment. Baseline of monthly seizure frequency was calculated within 3 months prior to VNS placement. Monthly seizure frequency was assessed at different points along the timeline: 3 months before ANT-DBS implantation as well as 3, 6, 12, 24, 36, 48, 60, and 72 months after ANT-DBS device placement. At each time point, seizure frequency was compared to baseline.Results:Six patients were implanted with ANT-DBS. Three (50%) patients had multifocal epilepsy, one (16.6%) had focal epilepsy, and two (33.4%) had combined generalized and focal epilepsy. Two ...

Lecture Notes in Computer Science, 2005

Neuromodulation, Aug 1, 2022

bioRxiv (Cold Spring Harbor Laboratory), Mar 26, 2020

The zona incerta (ZI) is a small gray matter region of the deep brain first identified in the 19t... more The zona incerta (ZI) is a small gray matter region of the deep brain first identified in the 19th century, yet direct in vivo visualization and characterization has remained elusive. Noninvasive detection of the ZI and surrounding region could be critical to further our understanding of this widely connected but poorly understood deep brain region and could contribute to the development and optimization of neuromodulatory therapies. We demonstrate that high resolution (submillimetric) longitudinal (T1) relaxometry measurements at high magnetic field strength (7 Tesla) can be used to delineate the ZI from surrounding white matter structures, specifically the fasciculus cerebellothalamicus, fields of Forel (fasciculus lenticularis, fasciculus thalamicus, field H), and medial lemniscus. Using this approach, we successfully derived in vivo estimates of the size, shape, location, and tissue characteristics of substructures in the ZI region, confirming observations only previously possible through histological evaluation that this region is not just a space between structures but contains distinct morphological entities that should be considered separately. Our findings pave the way for increasingly detailed in vivo study and provide a structural foundation for precise functional and neuromodulatory investigation. .

World Neurosurgery, Feb 1, 2020

BACKGROUND /Objective: The role of trainee involvement in lesioning procedures for trigeminal neu... more BACKGROUND /Objective: The role of trainee involvement in lesioning procedures for trigeminal neuralgia (TN) has not been investigated in the literature. The objective of this study was to compare the complications and efficacy of percutaneous glycerol rhizotomy (GR) as performed by staff neurosurgeons and trainees. METHODS A retrospective chart analysis of 165 patients with medically-refractory TN undergoing 293 GR procedures by either a staff attending (n=156) or trainee (n=137) in between 2007 to 2018 were analyzed with respect to procedure time, fluoroscopy time and radiation exposure, complication rates and outcome. RESULTS There was no difference in procedure duration between teaching and non-teaching cases and only a non-significant trend towards more fluoroscopy time for the latter. Initial response rates to GR were equal for staff attending (88.7%) and trainee cases (87.2%; p=0.708). Similarly, there was no statistically significant difference (p=0.48) between staff attending case median time to recurrence (1.6 ± 0.3 years) vs. that of the trainee cases (1.7 ± 0.3 years). Overall complications were low (7.5% overall). The occurrence of facial hypoesthesia correlated with the amount of injected glycerol (p<0.01). CONCLUSIONS GR for the treatment of TN can safely be performed by senior residents and fellows under supervision.

Canadian Journal of Neurological Sciences, Jun 1, 2016

Background: Glioblastoma is the most common primary malignant brain tumor. Primary Glioblastoma (... more Background: Glioblastoma is the most common primary malignant brain tumor. Primary Glioblastoma (PriGO) cells are key drivers of glioblastoma. Senescence is the irreversible growth arrest of cells with continued metabolic activity. Recently, I discovered PriGO cells undergo premature senescence in response to Fetal Bovine Serum (FBS). Determining the underlying molecular mechanisms may allow development of novel therapeutic strategies to decrease the malignant potential of glioblastoma. Methods: Global gene expression changes in PriGO cells treated with serum were analyzed and compared to untreated cells. Senescence was determined by the Senescence-Associated-Beta-Galactosidase (SA-B-Gal) assay. Results: PriGO cells treated with serum demonstrated increased expression of genes in the Transforming Growth Factor Beta (TGF-B) pathway, such as Thrombospondin 1 (TSP1), compared to untreated cells. TGF-B treatment of PriGO cells signifi cantly increased senescence compared to untreated cells. Treatment of PriGO cells with serum and the TGF-B inhibitor SB431542 led to a decrease in senescence compared to serum only treated cells. Treatment of PriGO cells with serum and the TSP1 inhibitor LSKL led to a reduction in senescence compared to serum only treated cells. Conclusions: Our data identifi es TGF-B as an important component of serum responsible for inducing senescence in PriGO cells. Furthermore, TGF-B induced senescence in PriGO cells is in part mediated by TSP1.

Canadian Journal of Neurological Sciences, Jul 10, 2020

Scientific Reports, May 19, 2020

Vertical current steering (vCS) divides current between multiple contacts, which reduces radial s... more Vertical current steering (vCS) divides current between multiple contacts, which reduces radial spread to fine-tune the electric field shape and improves neuroanatomical targeting. vCS may improve the variable responsiveness of Parkinsonian gait to conventional deep brain stimulation. We hypothesized that vCS elicits greater improvement in ambulation in Parkinson's disease patients compared to conventional, single-contact stimulation. vCS was implemented with divisions of 70%/30% and 50%/50% and compared to single-contact stimulation with four therapeutic window amplitudes in current-controlled systems. Walking at a self-selected pace was evaluated in seven levodopa-responsive patients. Integrative measures of gait and stimulation parameters were assessed with the functional ambulation performance (FAP) score and total electrical energy delivered (TEED), respectively. A twotailed Wilcoxon matched-pairs signed rank test assessed the effect of each stimulation condition on FAP and TEED and compared regression slopes; further, a two-tailed Spearman test identified correlations. vCS significantly lowered the TEED (P < 0.0001); however, FAP scores were not different between conditions (P = 0.786). Compared to single-contact stimulation, vCS elicited higher FAP scores with lower TEED (P = 0.031). FAP and TEED were positively correlated in vCS (P = 2.000 × 10-5 , r = 0.397) and single-contact stimulation (P = 0.034, r = 0.205). Therefore, vCS and single-contact stimulation improved ambulation similarly but vCS reduced the TEED and side-effects at higher amplitudes. Parkinson's disease and deep brain stimulation Deep brain stimulation (DBS) consistently relieves appendicular symptoms in Parkinson's disease (PD) but its effect on Parkinsonian gait deficits remains more elusive and variable 1. Thus, in present clinical practice, PD patients with severe postural and gait instabilities or levodopa (L-DOPA) resistant postural and gait instabilities are often excluded from receiving DBS 2-4. DBS chronically transmits electrical pulses from a sub-dermally implanted impulse generator (IPG) in the upper chest to neural tissue through implanted electrodes to address disabling dyskinesia and motor fluctuations from long-term use of L-DOPA 5. The varying response of Parkinsonian gait deficits to DBS may be attributed to extensive physiological integration of various networks necessary for gait facilitation, the influence of bradykinesia and rigidity on Parkinsonian gait deficits, and the bias of upper limb symptom improvement during contact localization and selection 6,7. Gait deficits attributed to rigidity and bradykinesia such as reduced step length and gait velocity tend to respond to L-DOPA and subthalamic nucleus (STN)-DBS. However, L-DOPA responsive gait deficits still exhibit a more variable responsiveness to STN-DBS as compared to appendicular symptoms such as tremor and rigidity. For instance, stimulation spread into the zona incerta and/or fields of forel from STN targeted electrodes has been reported to induce gait akinesia with a paradoxical improvement of dyskinesia, rigidity, and tremor 8,9. This outcome highlights the sensitivity of gait treatment to neuroanatomical targeting of the resultant stimulation. Three major goals of DBS programming are to 1) optimize symptom alleviation, 2) reduce side effects, and 3) limit IPG power consumption to reduce the battery drainage rate. Faster drainage of the IPG battery

Saudi Journal of Anaesthesia, Jul 1, 2008

Background: Awake craniotomy using local anaesthesia and monitored conscious sedation is widely u... more Background: Awake craniotomy using local anaesthesia and monitored conscious sedation is widely used for the excision of intracranial tumors or vascular abnormalities or for the management of refractory seizures. Propofol combined with remifentanil represents a popular technique for the provision of conscious sedation during these procedures. This study evaluated patient satisfaction following awake craniotomy performed under propofol-remifentanil sedation. The study also assessed the incidence of intraoperative and postoperative complications associated with this technique. Method: This prospective study evaluated the satisfaction of 25 adult patients undergoing awake craniotomy under propofol-remifentanil sedation. Evaluation involved interviewing patients at 1 hour, 24 hours, and 6 weeks postoperatively. Postoperative recall of pain, anxiety, and discomfort were assessed at 1 hour, 24 hours, and 6 weeks postoperatively. Surgeon and anesthesiologist satisfaction was also evaluated at the end of each procedure. Results: At 1 hour postoperative assessment, twenty-four patients (96%) were satisfied with the anesthetic technique. Patient satisfaction scores were similar at 1 hour, 24 hours and 6 weeks postoperatively. Twentyone of the twenty-four patients (84%) stated that they would choose the same anesthetic technique if they were to undergo the same procedure again. Surgeons and anesthesiologists were satisfied in twenty-three cases (92%). Conclusion: This study confirms that monitored conscious sedation with propofol-remifentanil is a useful alternative technique for awake craniotomy with a high patient, surgeon and anesthetist satisfaction.