Publications by authors named "Andrew G Parrent"

Article Synopsis
  • The study aimed to investigate the role of the posterior cingulate gyrus (PCG) in mesial temporal lobe seizures (MTLS) by reviewing SEEG recordings from patients with electrode implantation in the PCG.! -
  • Out of 97 patients analyzed, 9 patients with MTLS were included, revealing that the PCG was the primary site of seizure propagation in the majority of cases, indicating its importance in seizure spread.! -
  • The findings suggest that fast propagation to the PCG could be a sign of favorable surgical outcomes after temporal lobe surgery, highlighting the need for further research in this area.!
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Article Synopsis
  • * No significant differences were found between patients who had typical seizures (STS) and those who did not (non-STS) in demographics or epilepsy characteristics, but non-STS patients had fewer electrodes implanted and spent more time in the monitoring unit.
  • * Only a small percentage of non-STS patients underwent surgery, all of whom had typical seizures triggered during different tests, and there were cases of psychogenic non-epileptic seizures among them, but no predictive factors were identified for
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The availability of long-term (>2 years) safety outcomes of spinal cord stimulation (SCS) remains limited. We evaluated safety in a global SCS registry for chronic pain. Participants were prospectively enrolled globally at 79 implanting centers and followed out to 3 years after device implantation.

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Background: Electrical stimulation mapping (ESM) is an important tool for the localization of the seizure onset zone (SOZ) in patients with medically resistant epilepsy (MRE). ESM is the gold standard for the identification of eloquent cortex in epilepsy surgery candidates. However, there is no standard protocol outlining how to perform ESM, to obtain the most useful information possible.

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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.

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Objective: Changes of dream ability and content in patients with brain lesions have been addressed in only about 100 case reports. All of these reports lack data regarding prelesional baseline dream content. Therefore, it was the objective of this study to prospectively assess dream content before and after anterior temporal lobectomy.

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Objective: We have provided long-term data on clinically meaningful pain alleviation for drug-refractory headache disorders using occipital (ONS) and supraorbital nerve stimulation (SONS).

Methods: We performed a retrospective review of 96 patients with migraine, cervicogenic headache, cluster headache, neuropathic pain of the scalp, tension-type headache, and new daily persistent headache who had undergone ONS (61.5%), SONS (11.

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Purpose: To provide a descriptive analysis on the presurgical evaluation and surgical management of a cohort of patients with stroke related epilepsy (SRE).

Methods: We retrospectively examined the clinical characteristics, results of non-invasive and invasive presurgical evaluation, surgical management and outcome of consecutive patients with drug-resistant SRE in our institution from January 1, 2013 to January 1, 2020.

Results: Twenty-one of 420 patients (5%) who underwent intracranial EEG (iEEG), resective epilepsy surgery and/or vagus nerve stimulation (VNS) placement, had SRE.

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Objective: To describe morphological characteristics of the brainstem nuclei in response to chronic vagus nerve stimulation (VNS) in patients with refractory epilepsy.

Background: VNS is a treatment option for individuals with medically refractory epilepsy. While treatment with VNS may achieve up to 50% seizure reduction and is protective against sudden unexpected death in epilepsy (SUDEP), its mechanism of action is not fully understood.

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Objective: To determine the contribution of stereo-EEG for localization purpose in patients with a visible lesion on MRI.

Background: Intracranial EEG is often used to localize the epileptogenic focus in patients with non-lesional focal epilepsy. Its role in cases where a lesion is visible on MRI can be even more complex and the relationship between the lesion and the seizure onset has rarely been addressed.

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Objective: 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.

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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 T) can be used to delineate the ZI from surrounding white matter structures, specifically the fasciculus cerebellothalamicus, fields of Forel (fasciculus lenticularis, fasciculus thalamicus, and field H), and medial lemniscus.

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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.

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Background: Both stereoelectroencephalography (SEEG) and subdural strip electrodes (SSE) are used for intracranial electroencephalographic recordings in the invasive investigation of patients with drug-resistant epilepsy.

Objective: To compare SEEG and SSE with respect to feasibility, complications, and outcome in this single-center study.

Methods: Patient characteristics, periprocedural parameters, complications, and outcome were acquired from a pro- and retrospectively managed databank to compare SEEG and SSE cases.

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Background: "Temporal plus" epilepsy (TPE) is a term that is used when the epileptogenic zone (EZ) extends beyond the boundaries of the temporal lobe. Stereotactic electroencephalography (SEEG) has been essential to identify additional EZs in adjacent structures that might be part of the temporal lobe/limbic network.

Objective: We present a small case series of temporal plus cases successfully identified by SEEG who were seizure-free after resective surgery.

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Objective: The role of trainee involvement in lesioning procedures for trigeminal neuralgia (TN) has not yet been investigated in reported studies. The objective of the present study was to compare the complications and efficacy of percutaneous glycerol rhizotomy (GR) when performed by staff neurosurgeons and trainees.

Methods: A retrospective medical record analysis of 165 patients with medically refractory TN who had undergone 293 GR procedures by either a staff attending (n = 156) or trainee (n = 137) from 2007 to 2018 was performed.

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Background: The insula is a deep cortical structure that has renewed interest in epilepsy investigation. Invasive EEG recordings of this region have been challenging. Robot-assisted stereotactic electroencephalography has improved feasibility and safety of such procedures.

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Accurate spatial correspondence between template and subject images is a crucial step in neuroimaging studies and clinical applications like stereotactic neurosurgery. In the absence of a robust quantitative approach, we sought to propose and validate a set of point landmarks, anatomical fiducials (AFIDs), that could be quickly, accurately, and reliably placed on magnetic resonance images of the human brain. Using several publicly available brain templates and individual participant datasets, novice users could be trained to place a set of 32 AFIDs with millimetric accuracy.

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Objective: The prevalence of trigeminal neuralgia (TN) in patients with multiple sclerosis (MS-TN) is higher than in the general population (idiopathic TN [ITN]). Glycerol rhizotomy (GR) is a percutaneous lesioning surgery commonly performed for the treatment of medically refractory TN. While treatment for acute pain relief is excellent, long-term pain relief is poorer.

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In the rodent cerebral circulation, inward rectifying K (K) channels set resting tone and the distance over which electrical phenomena spread along the arterial wall. The present study sought to translate these observations into human cerebral arteries obtained from resected brain tissue. Computational modeling and a conduction assay first defined the impact of K channels on electrical communication; patch-clamp electrophysiology, quantitative PCR, and immunohistochemistry then characterized K2.

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Intradiploic cerebrospinal fluid cysts are rare entities that have been reported to occur following trauma and surgery. We present a case of a 53-year-old female patient with an incidental intradipoloic cerebrospinal fluid cyst in communication with a Dandy-Walker malformation, likely related to a remote history of childhood surgery for occipital encephalocele.

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At the London Health Sciences Centre Epilepsy Program, stereotactically implanted depth electrodes have largely replaced subdural electrodes in the presurgical investigation of patients with drug-resistant epilepsy over the past 4 years. The rationale for this paradigm shift was more experience with, and improved surgical techniques for, stereoelectroencephalography, a possible lower-risk profile for depth electrodes, better patient tolerability, shorter operative time, as well as increased recognition of potential surgical targets that are not accessible to subdural electrodes.

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Background: Connectivity studies targeting the thalamus have revealed patterns of atrophy and deafferentiation in temporal lobe epilepsy (TLE). The thalamus can be parcellated using probabilistic tractography to demonstrate regions of cortical connectivity; however, sensitivity to smaller or less connected regions is low.

Purpose/hypothesis: To investigate thalamic structural connectivity in a wider range of cortical and limbic structures in TLE patients using a novel connectivity map normalization procedure.

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Background: During Leksell frame-based stereotaxy the lateral trajectory can be obstructed by the arc supports at certain combinations of the X-coordinate and arc angle.

Objective: To provide a matrix with usable and prohibited combinations of the X-coordinate and arc angle to faciliate finding lateral stereotactic trajectories with the Leksell frame in standard configuration.

Methods: Various combination settings of the X-coordinate and arc angle were tested for a Leksell Multi-Purpose Stereotactic Arc mounted on a Leksell Coordinate Frame G.

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Background: For intracranial electroencephalographic monitoring, stereotactically implanted depth electrodes are increasingly used at epilepsy centers around the world.

Objective: To identify pearls and pitfalls from our experience with stereotactic Leksell (Elekta AB, Stockhom, Sweden) frame-based depth electrode implantation.

Methods: An intraoperative video of the implantation technique was recorded.

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