Insular mapping: correlate to MRI diagnosis and treatment assessment in epilepsy and brain tumor
Poster No:
11
Submission Type:
Abstract Submission
Authors:
Lee Cheng-Chia1
Institutions:
1Taipei Veterans General Hospital, Taipei, Taiwan
First Author:
Introduction:
Insular lobe located in the deep of the brain, usually medial side of the frontal operacula and temporal opercula. The insula is part of the limbic system, and an important portion of the Papez circuit with extensive and complicated functional connectivity. Due to the deep and central location of the brain, the epileptologists sometimes have difficulties to identify the seizures origin from the insula. For some selected cases, the invasive electroencephalography (EEG) recording is required. Since 2000, the patients with insular epilepsy would undergo invasive EEG recording via subdural strips and grids in Taipei Veteran General Hospital. After 2013, the stereo-electroencephalography (SEEG) is exclusively used for the insula-related epilepsy (including temporal plus epilepsy, or extratemporal epilepsy). Following the methodology introduced from the group of the Saint Anne Hospital in Paris (France) in 1974., epileptologists work hard to identify the cingulate gyrus which specific ictal and interictal patterns develop a seizure. The goal of this study is to evaluate the localization of epileptogenic zone, and the epilepsy network, and establish a validation system for epilepsy networks based on SEEG.
Methods:
In this study, the function of the cortical area can be localized through the deep electrodes of SEEG (stereo-electroencephalography). In the past, before the advent of SEEG, direct electrical stimulation of the insula was almost impossible. With the intervention of SEEG, direct electrophysiological mapping of the insula's function has become feasible and serves as a complement to fMRI findings over the past decade. Below is the description of the clinical procedure for electrical stimulation:
Phase 1: Low-frequency Electrical Stimulation
Setting: Frequency 1 Hz, pulse duration 1000 µs, total duration 20-40 seconds, intensity 0.5-3 mA.
Low-frequency stimulation is applied to pairs of adjacent electrodes in the SEEG array. If the patient experiences any symptoms, the clinical symptoms and corresponding SEEG responses are recorded. Generally, low-frequency stimulation only induces symptoms in the eloquent cortex, particularly in the primary motor cortex.
Phase 2: High-frequency Electrical Stimulation
Setting: Frequency 50 Hz, pulse duration 250-500 µs, total duration 3-7 seconds, intensity 0.5-3 mA.
This phase adjusts the parameters based on the results of the first phase. Due to the higher energy output in this phase, there is an increased risk of afterdischarge. To avoid this, stimulation is applied in a staggered manner, such as stimulating the anterior medial cortex first and then stimulating the posterior lateral cortex, ensuring that the time interval between stimulations is sufficient and preventing the electrodes from being too close to each other, which could lead to false positives or false negatives in the clinical outcome. High-frequency stimulation is more likely to induce clinical symptoms, including motor, sensory, visual, auditory, and language functions.
Phase 1: Low-frequency Electrical Stimulation
Setting: Frequency 1 Hz, pulse duration 1000 µs, total duration 20-40 seconds, intensity 0.5-3 mA.
Low-frequency stimulation is applied to pairs of adjacent electrodes in the SEEG array. If the patient experiences any symptoms, the clinical symptoms and corresponding SEEG responses are recorded. Generally, low-frequency stimulation only induces symptoms in the eloquent cortex, particularly in the primary motor cortex.
Phase 2: High-frequency Electrical Stimulation
Setting: Frequency 50 Hz, pulse duration 250-500 µs, total duration 3-7 seconds, intensity 0.5-3 mA.
This phase adjusts the parameters based on the results of the first phase. Due to the higher energy output in this phase, there is an increased risk of afterdischarge. To avoid this, stimulation is applied in a staggered manner, such as stimulating the anterior medial cortex first and then stimulating the posterior lateral cortex, ensuring that the time interval between stimulations is sufficient and preventing the electrodes from being too close to each other, which could lead to false positives or false negatives in the clinical outcome. High-frequency stimulation is more likely to induce clinical symptoms, including motor, sensory, visual, auditory, and language functions.
Results:
The insula was found to be a very eloquent cortical structure as its stimulation evoked a clinical response very frequently. Attached figure demonstrated a total of 42 enrolled patients who underwent SEEG monitoring and mapping. If we observed via the number of electrode contacts, a total of 402 contacts in insular cortex was located and the positive clinical response can be seen in 266 contacts (66.2%).
Conclusions:
We hope that this project is able to assist neurophysiological physicians making diagnosis with more evidence and to provide an integrated repot about insular function and the role of it in the neural network.
Brain Stimulation:
Direct Electrical/Optogenetic Stimulation 1
Invasive Stimulation Methods Other 2
Neuroanatomy, Physiology, Metabolism and Neurotransmission:
Anatomy and Functional Systems
Novel Imaging Acquisition Methods:
Anatomical MRI
EEG
Keywords:
Epilepsy
MRI
1|2Indicates the priority used for review
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