Andrew Parrent

The University of Western Ontario | UWO · Department of Clinical Neurological Sciences

Background: Studies of deep brain stimulation (DBS) require accurate electrode localization and image registration. We used anatomical fiducials to investigate localization and registration errors in patients who underwent subthalamic nucleus (STN) DBS for Parkinson’s disease (PD). Methods: We conducted a retrospective analysis of patients who unde...

Background and Objectives The efficacy of deep brain stimulation of the anterior nucleus of the thalamus (ANT DBS) in drug resistant epilepsy (DRE) patients was demonstrated in the double-blind Stimulation of the Anterior Nucleus of the Thalamus for Epilepsy (SANTE) randomized controlled trial. The Medtronic Registry for Epilepsy (MORE) aims to und...

Background: Therapeutic response from subthalamic nucleus (STN) deep brain stimulation (DBS) for Parkinson disease (PD) has been associated with proximity to an ideal target, commonly in the dorsal sensorimotor STN. Automated registration and atlas-based segmentation has allowed for contact localization within STN subnuclei. We sought to apply thes...

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 obta...

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...

Background: For patients with generalized epilepsy who do not respond to anti-seizure medications, the therapeutic options are limited. Vagus nerve stimulation (VNS) is a treatment mainly approved for therapy resistant focal epilepsy. There is limited information on the use of VNS on generalized epilepsies, including Lennox Gastaut Syndrome(LGS) an...

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. METHODS Usin...

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 su...

Objective: To provide long-term data on clinically meaningful pain alleviation in drug-refractory headache disorders with occipital and supraorbital nerve stimulation (ONS; SONS). Methods: Retrospective review of 96 patients suffering from migraine, cervicogenic headache, cluster headache, neuropathic pain of the scalp, tension-type headache and...

Background: There are no effective symptomatic treatments for progressive supranuclear palsy (PSP). Recent studies report benefits of spinal cord stimulation (SCS) for freezing of gait (FOG) and gait disorders in Parkinson's disease and atypical Parkinsonism patients. This is the first study to report therapeutic effects of SCS in Richardson's syn...

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...

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), wer...

Background For patients with generalized epilepsy who do not respond to antiseizure medications, the therapeutic options are limited. Vagus nerve stimulation (VNS) is a treatment mainly approved for therapy-resistant focal epilepsy. There is limited information on the use of VNS on generalized epilepsies, including Lennox–Gastaut Syndrome (LGS) and...

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 ob...

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...

Spinal Cord Stimulation Therapy for Gait Dysfunction in Two Corticobasal Syndrome Patients - Olivia Samotus, Andrew Parrent, Mandar Jog

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 ambulati...

Eating Epilepsy (EE) is a rare and often under-recognized form of reflex epilepsy, which manifests with seizures triggered during meals, with or without spontaneous seizures. The electro-clinical manifestations of EE are distinct with variable response to anti-seizures drugs. We report the case of a 34-year-old man who was seen for a 4-year history...

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. Meth...

The zona incerta (ZI) is a small deep brain region first identified in the 19th century, yet direct in vivo visualization and characterization has remained elusive. Noninvasive detection is critical to further our understanding of this widely connected but poorly understood region and could contribute to the development and optimization of neuromod...

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 smal...

Super obesity with a body mass index (BMI) >50 kg/m² presents a challenge for the neuroanesthesiologist during awake craniotomy procedures and poses increased perioperative risk of complications, even vis-à-vis morbid obesity. This article presents a super obese patient (BMI 57 kg/m²) with drug-refractory epilepsy and obstructive sleep apnea who un...

Background Orthostatic tremor is a rare hyperkinetic movement disorder that is characterized by a 13–18 Hz tremor in both legs while standing. Deep-brain stimulation of the caudal zona incerta has re-emerged as an alternate target for tremor control in various etiologies. Object Explore the clinical efficacy and mechanism of action of caudal zona...

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 cha...

COVER ILLUSTRATION Stylized illustration of the anatomical fiducials (AFIDs) framework published in this issue. The red circles mark the 10 midline AFIDs described in the article superimposed onto an artistic rendering of the MNI2009b template (mid‐sagittal slice). The double circles and grayscale gradient depict some of the uncertainty and variabi...

Objective: Vagus Nerve Stimulation (VNS) is a neuromodulation device approved for the treatment of medically refractory epilepsy. Worldwide, only 35 cases of pregnancies that has been described. This study aims to continue to increase the limited knowledge of the use of VNS during pregnancy. Methods: We interrogated the database of the Epilepsy...

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. Objective: To describe technical nuances of three-dimensional (3D) obliqu...

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 rel...

Background: The zona incerta (ZI) is a small structure in the deep brain first identified by Auguste Forel for which robust in vivo visualization has remained elusive. The increased inherent signal from ultra-high field (7-Tesla or greater; 7T) magnetic resonance imaging (MRI) presents an opportunity to see structures not previously visible. In thi...

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 p...

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 rel...

Intradiploic cerebrospinal fluid cysts are rare entities which have been reported to occur following trauma and surgery. We present a case of 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.

Background : The hippocampus can be divided longitudinally into the head, body, and tail; and unfolded medial-to-laterally into the subiculum, cornu ammonis (CA) sectors, and the dentate gyrus. Ultra-high field (≥ 7 Tesla; 7T) magnetic resonance imaging (MRI) enables submillimetric visualization of these hippocampal substructures which could be val...

Introduction Reflex epilepsy is characterized by seizures that are triggered by internal or external stimuli. Based on the complexity of the trigger, the reflex epilepsies can be subdivided into simple and complex. Eating Epilepsy (EE) is a subtype of the complex reflex epilepsies and represents a heterogeneous electro-clinical syndrome. The body o...

Introduction Epilepsy arising from the insula is widely regarded as a challenging type of seizure, probably owing to the deep-seated location of the insula and the extensive connections it makes with adjacent structures. In recent years, we have rapidly gained insights into insular epilepsy-related obstacles. Here, we describe a detailed analysis o...

Introduction The VNS (Vagus Nerve Stimulation) is a type of neuromodulation therapy used in patients with focal epilepsy, usually reserved for those who are not candidates for resective surgery. The initial aprovation was for focal epilepsy. The range of seizure frequency reduction of 50% or more were 40% in the study of Panebianco et al. (2015) an...

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, stereoelec...

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 inve...

Background: Benefits of dopaminergic therapy and deep brain stimulation are limited and unpredictable for axial symptoms in Parkinson's disease. Dorsal spinal cord stimulation may be a new therapeutic approach. The objective of this study was to investigate the therapeutic effect of spinal cord stimulation on gait including freezing of gait in adv...

Background: Intraoperative sedation is often used to facilitate deep brain stimulation (DBS) surgery; however, these sedative agents also suppress microelectrode recordings (MER). To date, there have been no studies that have examined the effects of differing sedatives on surgical outcomes and the success of DBS surgery. Methods: We performed a...

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 intraoper...

Background: Morphometry and connectivity studies targeting the thalamus have revealed specific patterns of atrophy and deafferentiation in patients with temporal lobe epilepsy (TLE). We used probabilistic tractography to investigate thalamic connectivity with respect to duration of epilepsy and surgical outcomes in TLE. Methods: Patients (N=20) wit...

Background Template and atlas guidance are fundamental aspects of stereotactic neurosurgery. The recent availability of ultra-high field (7 Tesla) magnetic resonance imaging has enabled in vivo visualization at the submillimeter scale. In this Doing More with Less article, we describe our experiences with integrating ultra-high field template data...

Background: Spinal cord stimulation (SCS) is a well-established treatment for chronic neuropathic pain in the lower limbs. However, some patients have pain in distributions that are difficult to target specifically and consistently with SCS. This often involves pain in the groin or upper limbs, or pain limited to a specific dermatome. We hypothesi...

Ultra-high field magnetic resonance imaging (MRI) provides superior visualization of brain structures compared to lower fields, but images may be prone to severe geometric inhomogeneity. We propose to quantify local geometric distortion at ultra-high fields in in vivo datasets of human subjects scanned at both ultra-high field and lower fields. By...

Background: Spinal cord stimulation (SCS) is a well-established treatment for chronic neuropathic pain in the lower limbs. Upper limb pain comprises a significant proportion of neuropathic pain patients, but is often difficult to target specifically and consistently with paresthesias. We hypothesized that the use of dorsal nerve root stimulation (...

Background: Temporal lobe epilepsy (TLE) with unclear lateralization may require intracranial implantation of electrodes (IIE). We retrospectively assessed the association between the use of IIE and long-term outcomes in patients undergoing anterior temporal lobectomy (ATL). Participants and methods: We retrospectively reviewed the records of 1,...

Background: Chronic neuropathic groin pain is a common problem. It can arise following surgery or trauma, or spontaneously as part of various pelvic pain syndromes. A number of different stimulation techniques have been reported in the literature to treat this area, but due to the complex anatomy of the region, it can be difficult to target effect...

Purpose: To provide a more detailed investigation of hippocampal subfields using 7T magnetic resonance imaging (MRI) for the identification of hippocampal sclerosis in temporal lobe epilepsy (TLE). Materials and methods: Patients (n = 13) with drug-resistant TLE previously identified by conventional imaging as having hippocampal sclerosis (HS) o...

Study design: Clinical practice guidelines. Objectives: The project objectives were to develop the first Canadian recommendations on a model of care for the management of at- and below-level neuropathic pain in people with spinal cord injury (SCI). Setting: The guidelines are relevant for inpatient and outpatient SCI rehabilitation settings i...

Study design: Clinical practice guidelines. Objectives: The objective was to develop the first Canadian clinical practice guidelines for the management of neuropathic pain in people with spinal cord injury (SCI). Setting: The guidelines are relevant for inpatient and outpatient SCI rehabilitation settings in Canada. Methods: The guidelines were dev...

Immunosuppressive therapy is a risk factor for lymphoproliferative disorders. We present a case of primary CNS B-cell lymphoma in the setting of iatrogenic immunosuppression from azathioprine usage. A literature review is provided. Methods: Case report Results: 64-year-old male presents with several weeks of cognitive decline, impaired speech, and...

Polymicrogyria (PMG), a malformation of cortical development, describes an area of cerebral cortex with excessively small convolutions. This study examines the clinical spectrum of epilepsy associated with PMG, a condition which commonly presents as medically-refractory epilepsy. Methods: All patients investigated in the Epilepsy Monitoring Unit fr...

Purpose Deep brain stimulation (DBS) is a common treatment for Parkinson’s disease (PD) and involves the use of brain atlases or intrinsic landmarks to estimate the location of target deep brain structures, such as the subthalamic nucleus (STN) and the globus pallidus pars interna (GPi). However, these structures can be difficult to localize with c...

Objectives: Our aim is to assess the subfield-specific histopathological correlates of hippocampal volume and intensity changes (T1, T2) as well as diff!usion MRI markers in TLE, and investigate the efficacy of quantitative MRI measures in predicting histopathology in vivo. Experimental design: We correlated in vivo volumetry, T2 signal, quantit...

Cranial nerve (CN) deficits following anterior temporal lobectomy (ATL) are an uncommon but well-recognized complication. The usual CNs implicated in post-ATL complications include the oculomotor, trochlear, and facial nerves. To the authors' knowledge, injury to the trigeminal nerve leading to neuropathic pain has not been previously described in...

Malformations of cortical development are disturbances in brain formation that arise from abnormalities affecting the processes of cortical development. Surgical treatment of intractable epilepsy in patients with malformations of cortical development requires localization of both epileptogenic and eloquent cortices. Functional magnetic resonance im...

Clinical scale-based follow-up of patients undergoing bilateral subthalamic deep brain stimulation (STN-DBS) surgery has shown inconsistent effects on bradykinesia in Parkinson's disease patients. Furthermore, quantitative assessment of STN-DBS effect on bradykinesia has not been fully explored yet. Our group uses multisensory kinematic technologie...

Objective To investigate the histopathological correlates of quantitative relaxometry and DTI and determine their efficacy in epileptogenic lesion detection for pre-operative evaluation of focal epilepsy. Methods We correlated quantitative relaxometry and DTI with histological features of neuronal density and morphology in 55 regions of the tempora...

BACKGROUND: Based on a prior needs-based questionnaire performed by our group, qualitative evidence suggests that neurosurgeons feel that image processing techniques can lead to safer and more effective operations. A wealth of image processing applications has been developed over the past several decades for the facilitation of improved surgical pl...

Objective: Malformations of cortical development (MCD) are an increasingly recognized cause of medically intractable epilepsy. We assessed the role of fMRI in evaluating the motor and somatosensory cortices, as well as if there is possible reorganization of these vital areas in patients with polymicrogyria. Methods: We included 2 patients with p...

Purpose. To review the postoperative seizure outcomes of patients that underwent surgery for epilepsy at King Faisal Specialist Hospital & Research Centre (KFSHRC). Methods. A descriptive retrospective study for 502 patients operated on for medically intractable epilepsy between 1998 and 2012. The surgical outcome was measured using the ILAE criter...

Seizure recurrence after epilepsy surgery has been classified as either early or late depending on the recurrence time after operation. However, time of recurrence is variable and has been arbitrarily defined in the literature. We established a mathematical model for discriminating patients with early or late seizure recurrence, and examined differ...

Cell-based therapies offer promise for patients with Parkinson's disease (PD); however, durable and effective transplantation substrates need to be defined. This study characterized the feasibility and growth properties of primary cultures established from small-volume brain biopsies taken during deep brain stimulation (DBS) surgery in patients wit...

We developed novel methodology for investigating the use of quantitative relaxometry (T1, T2) and diffusion tensor imaging (DTI) for lateralization in temporal lobe epilepsy. Patients with mesial temporal sclerosis confirmed by pathology (N = 8) and non-MTS unilateral temporal lobe epilepsy (N = 6) were compared against healthy controls (N = 19) us...

There have been significant advances in stimulation of the central nervous system applied to epilepsy over the last couple of decades. A number of similarities arise, regardless of target: there appears to be a latency to beneficial effect, and there appears to be progressive improvement in the degree of seizure reduction in responders over a perio...

Temporal lobe epilepsy (TLE) is the most common form of medically intractable epilepsy. Advances in electrophysiology and neuroimaging have led to a more precise localization of the epileptogenic zone within the temporal lobe. Resective surgery is the most effective treatment for TLE. Despite the variability in surgical techniques and in the extent...

Objective: During epilepsy surgery it is important for the surgeon to correlate the preoperative cortical morphology (from preoperative images) with the intraoperative environment. Augmented Reality (AR) provides a solution for combining the real environment with virtual models. However, AR usually requires the use of specialized displays, and its...

This article can be accessed at: http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9340764&fulltextType=MR&fileId=S031716710001194X