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A Concept Car or an All-road Car To Drive All Along Glioma Resection?
Letters to the Editor A Concept Car or an All-road Car To Drive All Along Glioma Resection? LETTER: reading the recent article by Ogawa et al. (3). They W eareenjoyed to be congratulated for this original and promising study, which shows how the real-time localization of high gamma activity (HGA) using intraoperative electrocorticography can reliably help identifying motor and language cortical areas before glioma resection. The main result of this case series (4 malignant gliomas) is that HGA mapping with electrocorticography seems to accurately localize motor and language cortical areas with excellent sensitivity and specificity. We wonder how Ogawa et al. (3) correlated the HGA electrocorticographic mapping together with the direct electrocortical stimulation mapping. Do they restrict direct electrocortical stimulations on HGA-positive sites or do they perform it on the whole cortex, including HGA-negative areas? This should be done to ensure the accurate definition of specificity and sensitivity of HGA electrocorticographic mapping. Another interesting finding is that HGA electrocorticographic mapping, which is a kind of electrophysiologic correlate of blood oxygenation level-dependent responses, appears to remain reliable even in the context of highly perfused gliomas (high-grade of malignancy, contrast enhancement), whereas functional magnetic resonance imaging (MRI) shares poor specificity and sensitivity for motor and language cortical mapping in this context. Indeed, a recent study underlined that functional MRI is insufficiently sensitive for accurate language mapping in patients with gliomas and demonstrated that higher grade tumors and highly perfused tumors (with high relative cerebral blood volume) significantly alter functional MRI reliability (2).
with direct electric stimulation remains the best (and the only) option to obtain a real-time and “all-road” map all along the resection. Johan Pallud1,2 From the 1Department of Neurosurgery, Sainte-Anne Hospital and 2Paris Descartes University, Paris, France To whom correspondence should be addressed: Johan Pallud, M.D., Ph.D. [E-mail: [email protected]] Published online 26 February, 2015; http://dx.doi.org/10.1016/j.wneu.2015.02.022.
REFERENCES 1. Duffau H: A new concept of diffuse (low-grade) glioma surgery. Adv Tech Stand Neurosurg 38:3-27, 2012. 2. Kuchcinski G, Mellerio C, Pallud J, Dezamis E, Turc G, Rigaux-Viodé O, Malherbe C, Roca P, Leclerc X, Varlet P, Chrétien F, Devaux B, Meder JF, Oppenheim C: Three-tesla functional MR language mapping: comparison with direct cortical stimulation in gliomas. Neurology 84:560-568, 2015. 3. Ogawa H, Kamada K, Kapeller C, Hiroshima S, Prueckl R, Guger C: Rapid and minimum invasive functional brain mapping by real-time visualization of high gamma activity during awake craniotomy. World Neurosurg 82:912.e1-912.e10, 2014. 4. Pallud J, Capelle L, Huberfeld G: Tumoral epileptogenicity: how does it happen? Epilepsia 54:29-33, 2013. 5. Pallud J, Le Van Quyen M, Bielle F, Pellegrino C, Varlet P, Labussiere M, Cresto N, Dieme MJ, Baulac M, Duyckaerts C, Kourdougli N, Chazal G, Devaux B, Rivera C, Miles R, Capelle L, Huberfeld G: Cortical GABAergic excitation contributes to epileptic activities around human glioma. Science Translational Medicine 6: 244ra89, 2014.
The Road to Nonawaking Functional Mapping Combining High Gamma Activity with Corticocortical Evoked Potential
Such a real-time identification of HGA in the vicinity of glioma may help refining the surgical management of glioma-related seizures as it may allow the accurate location of epileptogenic foci that are nested within the infiltrated neocortex (4, 5). Did Ogawa et al. (3) record interictal or ictal epileptic activities together with HGA? Did such epileptic activities correlate with a particular HGA pattern? Do they observe artifacts during HGA electrocortical recordings that were induced by direct electrocortical stimulation or by seizures?
appreciate Dr. Johan Pallud’s careful reading of and W einstructive comments provided on our article in WORLD
Last, Ogawa et al. (3) report that the HGA electrocorticographic mapping is shorter than the direct electrocortical stimulation mapping. They did not report the overall duration of the surgery and one should expect that technical adjustments required for HGA electrocorticographic mapping and the addition of the 2 mapping procedures lengthen it. Is it possible to perform the electrocorticographic mapping before or during patient awakening? It would be of great interest. However, the duration of the initial electrocortical stimulation mapping is not a critical point, as it takes no longer than 10e20 minutes for an experienced team. More important is the direct electrocortical and subcortical stimulation mapping that should be performed along the glioma resection. Here is the main limitation of this nice technique, as HGA electrocorticographic mapping does not allow the mapping of subcortical areas that are the key for large and safe surgical removal of infiltrative gliomas (1). In this way, corticosubcortical mapping
1. “Do the authors restrict direct electrocortical stimulations on high gamma activity (HGA)epositive sites, or do they perform it on the whole cortex, including HGA-negative areas?”
WORLD NEUROSURGERY 84 [1]: 187e188, JULY 2015
NEUROSURGERY (2). Dr. Pallud’s questions and suggestions are quite important and cover topics in which we are also interested. We have replied to each of his respective comments. We hope that this additional information will improve the understanding of our research. Moreover, we would greatly appreciate the opportunity to perform collaborative functional mapping research in cooperation with Dr. Pallud’s institute.
Answer: For direct electrocortical stimulation, all of the grids embedded on the cortex were stimulated. However, the maximum number of embedded channels was between 40 and 80, which is a limitation of this study. Ideally, sensitivity and specificity should be calculated using subdural grids that cover the entire brain, but this is not practical. In our study, we used all embedded HGA-positive and HGA-negative electrodes to calculate sensitivity and specificity. Another limitation of our study is that only 4 cases were reported. Abbreviations and Acronyms CCEP: Cortico-cortical evoked potential HGA: High gamma activity
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with direct electric stimulation remains the best (and the only) option to obtain a real-time and “all-road” map all along the resection. Johan Pallud1,2 From the 1Department of Neurosurgery, Sainte-Anne Hospital and 2Paris Descartes University, Paris, France To whom correspondence should be addressed: Johan Pallud, M.D., Ph.D. [E-mail: [email protected]] Published online 26 February, 2015; http://dx.doi.org/10.1016/j.wneu.2015.02.022.
REFERENCES 1. Duffau H: A new concept of diffuse (low-grade) glioma surgery. Adv Tech Stand Neurosurg 38:3-27, 2012. 2. Kuchcinski G, Mellerio C, Pallud J, Dezamis E, Turc G, Rigaux-Viodé O, Malherbe C, Roca P, Leclerc X, Varlet P, Chrétien F, Devaux B, Meder JF, Oppenheim C: Three-tesla functional MR language mapping: comparison with direct cortical stimulation in gliomas. Neurology 84:560-568, 2015. 3. Ogawa H, Kamada K, Kapeller C, Hiroshima S, Prueckl R, Guger C: Rapid and minimum invasive functional brain mapping by real-time visualization of high gamma activity during awake craniotomy. World Neurosurg 82:912.e1-912.e10, 2014. 4. Pallud J, Capelle L, Huberfeld G: Tumoral epileptogenicity: how does it happen? Epilepsia 54:29-33, 2013. 5. Pallud J, Le Van Quyen M, Bielle F, Pellegrino C, Varlet P, Labussiere M, Cresto N, Dieme MJ, Baulac M, Duyckaerts C, Kourdougli N, Chazal G, Devaux B, Rivera C, Miles R, Capelle L, Huberfeld G: Cortical GABAergic excitation contributes to epileptic activities around human glioma. Science Translational Medicine 6: 244ra89, 2014.
The Road to Nonawaking Functional Mapping Combining High Gamma Activity with Corticocortical Evoked Potential
Such a real-time identification of HGA in the vicinity of glioma may help refining the surgical management of glioma-related seizures as it may allow the accurate location of epileptogenic foci that are nested within the infiltrated neocortex (4, 5). Did Ogawa et al. (3) record interictal or ictal epileptic activities together with HGA? Did such epileptic activities correlate with a particular HGA pattern? Do they observe artifacts during HGA electrocortical recordings that were induced by direct electrocortical stimulation or by seizures?
appreciate Dr. Johan Pallud’s careful reading of and W einstructive comments provided on our article in WORLD
Last, Ogawa et al. (3) report that the HGA electrocorticographic mapping is shorter than the direct electrocortical stimulation mapping. They did not report the overall duration of the surgery and one should expect that technical adjustments required for HGA electrocorticographic mapping and the addition of the 2 mapping procedures lengthen it. Is it possible to perform the electrocorticographic mapping before or during patient awakening? It would be of great interest. However, the duration of the initial electrocortical stimulation mapping is not a critical point, as it takes no longer than 10e20 minutes for an experienced team. More important is the direct electrocortical and subcortical stimulation mapping that should be performed along the glioma resection. Here is the main limitation of this nice technique, as HGA electrocorticographic mapping does not allow the mapping of subcortical areas that are the key for large and safe surgical removal of infiltrative gliomas (1). In this way, corticosubcortical mapping
1. “Do the authors restrict direct electrocortical stimulations on high gamma activity (HGA)epositive sites, or do they perform it on the whole cortex, including HGA-negative areas?”
WORLD NEUROSURGERY 84 [1]: 187e188, JULY 2015
NEUROSURGERY (2). Dr. Pallud’s questions and suggestions are quite important and cover topics in which we are also interested. We have replied to each of his respective comments. We hope that this additional information will improve the understanding of our research. Moreover, we would greatly appreciate the opportunity to perform collaborative functional mapping research in cooperation with Dr. Pallud’s institute.
Answer: For direct electrocortical stimulation, all of the grids embedded on the cortex were stimulated. However, the maximum number of embedded channels was between 40 and 80, which is a limitation of this study. Ideally, sensitivity and specificity should be calculated using subdural grids that cover the entire brain, but this is not practical. In our study, we used all embedded HGA-positive and HGA-negative electrodes to calculate sensitivity and specificity. Another limitation of our study is that only 4 cases were reported. Abbreviations and Acronyms CCEP: Cortico-cortical evoked potential HGA: High gamma activity
www.WORLDNEUROSURGERY.org
187