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Resected Brain Tissue, Seizure Onset Zone and Quantitative EEG Measures: Towards Prediction of Post-Surgical Seizure Control.

Rummel C, Abela E, Andrzejak RG, Hauf M, Pollo C, Müller M, Weisstanner C, Wiest R, Schindler K - PLoS ONE (2015)

Bottom Line: If non-invasive methods alone do not allow to delineate the epileptogenic brain areas the surgical candidates undergo long-term monitoring with intracranial EEG.Despite of its great potential to assess the epileptogenicty of brain tissue, quantitative EEG analysis has not yet found its way into routine clinical practice.Using data-driven thresholding, quantitative EEG results were separated into normally contributing and salient channels.

View Article: PubMed Central - PubMed

Affiliation: Support Center for Advanced Neuroimaging (SCAN), University Institute for Diagnostic and Interventional Neuroradiology, Inselspital, Bern, Switzerland.

ABSTRACT

Background: Epilepsy surgery is a potentially curative treatment option for pharmacoresistent patients. If non-invasive methods alone do not allow to delineate the epileptogenic brain areas the surgical candidates undergo long-term monitoring with intracranial EEG. Visual EEG analysis is then used to identify the seizure onset zone for targeted resection as a standard procedure.

Methods: Despite of its great potential to assess the epileptogenicty of brain tissue, quantitative EEG analysis has not yet found its way into routine clinical practice. To demonstrate that quantitative EEG may yield clinically highly relevant information we retrospectively investigated how post-operative seizure control is associated with four selected EEG measures evaluated in the resected brain tissue and the seizure onset zone. Importantly, the exact spatial location of the intracranial electrodes was determined by coregistration of pre-operative MRI and post-implantation CT and coregistration with post-resection MRI was used to delineate the extent of tissue resection. Using data-driven thresholding, quantitative EEG results were separated into normally contributing and salient channels.

Results: In patients with favorable post-surgical seizure control a significantly larger fraction of salient channels in three of the four quantitative EEG measures was resected than in patients with unfavorable outcome in terms of seizure control (median over the whole peri-ictal recordings). The same statistics revealed no association with post-operative seizure control when EEG channels contributing to the seizure onset zone were studied.

Conclusions: We conclude that quantitative EEG measures provide clinically relevant and objective markers of target tissue, which may be used to optimize epilepsy surgery. The finding that differentiation between favorable and unfavorable outcome was better for the fraction of salient values in the resected brain tissue than in the seizure onset zone is consistent with growing evidence that spatially extended networks might be more relevant for seizure generation, evolution and termination than a single highly localized brain region (i.e. a "focus") where seizures start.

No MeSH data available.


Related in: MedlinePlus

Same neuroanatomical representation as in Fig 1 but for the first seizure of patient IV-1.The color code is as follows: red, channels included in the RBT; blue, channels belonging to the SOZ; black, channels NON that neither belonged to the RBT nor to the SOZ. In contrast to patient I-2 in Fig 1, there was no overlap OVL between SOZ and RBT. Channel labels are: FAL, frontal anterior left; FLL, frontal lateral left; TLPL, temporo-lateral to polar left; TBLL, temporo-basal left; TLPBL, temporo-lateral to parieto-basal left; TLCL, temporo-lateral to cranial left. A movie showing the contribution of all four measures on the implantation scheme in 3D is available in the supplementary material (S2 Movie).
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pone.0141023.g003: Same neuroanatomical representation as in Fig 1 but for the first seizure of patient IV-1.The color code is as follows: red, channels included in the RBT; blue, channels belonging to the SOZ; black, channels NON that neither belonged to the RBT nor to the SOZ. In contrast to patient I-2 in Fig 1, there was no overlap OVL between SOZ and RBT. Channel labels are: FAL, frontal anterior left; FLL, frontal lateral left; TLPL, temporo-lateral to polar left; TBLL, temporo-basal left; TLPBL, temporo-lateral to parieto-basal left; TLCL, temporo-lateral to cranial left. A movie showing the contribution of all four measures on the implantation scheme in 3D is available in the supplementary material (S2 Movie).

Mentions: In contrast to patient I-2 surgery outcome was unfavorable in patient IV-1 (Fig 3). Out of 62 implanted iEEG contacts, n = 59 channels recorded signals free of permanent artifacts. As the visually defined SOZ overlapped with the functional language area, it was decided to restrict palliative resection to the vicinity of the SOZ to minimize the risk of post-operative neurological deficits. In consequence, the overlap OVL between the visually defined SOZ (4 channels) and the RBT (2 channels) was empty. Retrospective qEEG analysis showed that in patient IV-1 large normalized node strength of the surrogate corrected mutual information matrix M were much more confined in space and time (panel t of Fig 4) than for patient I-2. Before and after the seizure salient values were mainly located in the left temporo-latero-posterio-basal iEEG channels TLPBL1 to TLPBL6, some of which were in the RBT and some of which in the SOZ (panels k and n). During the seizure, salient values were also visible on channels of the left temporo-latero-polar (TLPL) and left temporo-basal-lateral (TBLL) strip electrodes (panels l and m), which neither corresponded to the SOZ nor to the RBT. Throughout the peri-ictal recording the fraction of salient channels in the RBT was much lower than in patient I-2. Before and after seizure and were close to 0.5 (panels a and d). was smaller than in patient I-2 for any of the three zones of interest Z = {RBT,SOZ,OVL}. Only in the pre- and post-ictal phase the overlap with the SOZ came close to statistical significance (panel f).


Resected Brain Tissue, Seizure Onset Zone and Quantitative EEG Measures: Towards Prediction of Post-Surgical Seizure Control.

Rummel C, Abela E, Andrzejak RG, Hauf M, Pollo C, Müller M, Weisstanner C, Wiest R, Schindler K - PLoS ONE (2015)

Same neuroanatomical representation as in Fig 1 but for the first seizure of patient IV-1.The color code is as follows: red, channels included in the RBT; blue, channels belonging to the SOZ; black, channels NON that neither belonged to the RBT nor to the SOZ. In contrast to patient I-2 in Fig 1, there was no overlap OVL between SOZ and RBT. Channel labels are: FAL, frontal anterior left; FLL, frontal lateral left; TLPL, temporo-lateral to polar left; TBLL, temporo-basal left; TLPBL, temporo-lateral to parieto-basal left; TLCL, temporo-lateral to cranial left. A movie showing the contribution of all four measures on the implantation scheme in 3D is available in the supplementary material (S2 Movie).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4626164&req=5

pone.0141023.g003: Same neuroanatomical representation as in Fig 1 but for the first seizure of patient IV-1.The color code is as follows: red, channels included in the RBT; blue, channels belonging to the SOZ; black, channels NON that neither belonged to the RBT nor to the SOZ. In contrast to patient I-2 in Fig 1, there was no overlap OVL between SOZ and RBT. Channel labels are: FAL, frontal anterior left; FLL, frontal lateral left; TLPL, temporo-lateral to polar left; TBLL, temporo-basal left; TLPBL, temporo-lateral to parieto-basal left; TLCL, temporo-lateral to cranial left. A movie showing the contribution of all four measures on the implantation scheme in 3D is available in the supplementary material (S2 Movie).
Mentions: In contrast to patient I-2 surgery outcome was unfavorable in patient IV-1 (Fig 3). Out of 62 implanted iEEG contacts, n = 59 channels recorded signals free of permanent artifacts. As the visually defined SOZ overlapped with the functional language area, it was decided to restrict palliative resection to the vicinity of the SOZ to minimize the risk of post-operative neurological deficits. In consequence, the overlap OVL between the visually defined SOZ (4 channels) and the RBT (2 channels) was empty. Retrospective qEEG analysis showed that in patient IV-1 large normalized node strength of the surrogate corrected mutual information matrix M were much more confined in space and time (panel t of Fig 4) than for patient I-2. Before and after the seizure salient values were mainly located in the left temporo-latero-posterio-basal iEEG channels TLPBL1 to TLPBL6, some of which were in the RBT and some of which in the SOZ (panels k and n). During the seizure, salient values were also visible on channels of the left temporo-latero-polar (TLPL) and left temporo-basal-lateral (TBLL) strip electrodes (panels l and m), which neither corresponded to the SOZ nor to the RBT. Throughout the peri-ictal recording the fraction of salient channels in the RBT was much lower than in patient I-2. Before and after seizure and were close to 0.5 (panels a and d). was smaller than in patient I-2 for any of the three zones of interest Z = {RBT,SOZ,OVL}. Only in the pre- and post-ictal phase the overlap with the SOZ came close to statistical significance (panel f).

Bottom Line: If non-invasive methods alone do not allow to delineate the epileptogenic brain areas the surgical candidates undergo long-term monitoring with intracranial EEG.Despite of its great potential to assess the epileptogenicty of brain tissue, quantitative EEG analysis has not yet found its way into routine clinical practice.Using data-driven thresholding, quantitative EEG results were separated into normally contributing and salient channels.

View Article: PubMed Central - PubMed

Affiliation: Support Center for Advanced Neuroimaging (SCAN), University Institute for Diagnostic and Interventional Neuroradiology, Inselspital, Bern, Switzerland.

ABSTRACT

Background: Epilepsy surgery is a potentially curative treatment option for pharmacoresistent patients. If non-invasive methods alone do not allow to delineate the epileptogenic brain areas the surgical candidates undergo long-term monitoring with intracranial EEG. Visual EEG analysis is then used to identify the seizure onset zone for targeted resection as a standard procedure.

Methods: Despite of its great potential to assess the epileptogenicty of brain tissue, quantitative EEG analysis has not yet found its way into routine clinical practice. To demonstrate that quantitative EEG may yield clinically highly relevant information we retrospectively investigated how post-operative seizure control is associated with four selected EEG measures evaluated in the resected brain tissue and the seizure onset zone. Importantly, the exact spatial location of the intracranial electrodes was determined by coregistration of pre-operative MRI and post-implantation CT and coregistration with post-resection MRI was used to delineate the extent of tissue resection. Using data-driven thresholding, quantitative EEG results were separated into normally contributing and salient channels.

Results: In patients with favorable post-surgical seizure control a significantly larger fraction of salient channels in three of the four quantitative EEG measures was resected than in patients with unfavorable outcome in terms of seizure control (median over the whole peri-ictal recordings). The same statistics revealed no association with post-operative seizure control when EEG channels contributing to the seizure onset zone were studied.

Conclusions: We conclude that quantitative EEG measures provide clinically relevant and objective markers of target tissue, which may be used to optimize epilepsy surgery. The finding that differentiation between favorable and unfavorable outcome was better for the fraction of salient values in the resected brain tissue than in the seizure onset zone is consistent with growing evidence that spatially extended networks might be more relevant for seizure generation, evolution and termination than a single highly localized brain region (i.e. a "focus") where seizures start.

No MeSH data available.


Related in: MedlinePlus