Source Imaging in Mapping Eloquent Cortex December 6 th 2011

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1 Source Imaging in Mapping Eloquent Cortex December 6 th 2011 Samden Lhatoo, MD FRCP University Hospitals Case Medical Center American Epilepsy Society Annual Meeting

2 Disclosure Name of Commercial Interest Type of Financial Relationship None relevant to this presentation None American Epilepsy Society Annual Meeting

3 Learning Objectives Practicalities and pitfalls in source imaging of eloquent cortex Evidence base of electrical and magnetic source imaging of eloquent cortex Evidence based utility of electrical and magnetic source imaging of eloquent cortex in modern clinical practice American Epilepsy Society Annual Meeting

4 Why do we need Electromagnetic Source Imaging of Eloquent Cortex in Epilepsy Practice Pre-operative non-invasive localization of the primary hand, foot and face areas of the brain Relationship to lesions Relationship to central sulcus Craniotomy planning As alternatives to direct cortical stimulation and fmri Validation of source imaging techniques for epileptic spike and seizure localization

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7 Source Imaging of Eloquent Cortex in Epilepsy The somatosensory evoked potential preserved even in damaged hemispheres. Always in close relation to central sulcus The median SEP The posterior tibial SEP The lip SEP The auditory evoked potential The visual evoked potential Language area event-related potentials

8 Atlas of the Cerebral Sulci Michio Ono et al 1990

9 Source Imaging of Eloquent Cortex in Epilepsy Source imaging of the tibial SEP

10 16% 64% Atlas of the Cerebral Sulci Michio Ono et al %

11 Source Imaging of Eloquent Cortex in Epilepsy The median somatosensory evoked response N20/P20 Lüders et al: J of Neurosurg. 1983

12 Diagram 7 of Buchner 1. Brainstem response B P14 picked up by EEG but not MEG 2. N20/P20 modeled by a tangential T picked up by both MEG and EEG 3. P22 modeled by a radial R picked up by EEG but not MEG Buchner et al: Brain Topography, Volume 6, Number 4, 1994

13 Source Imaging of Eloquent Cortex in Epilepsy Requirements for accurate source imaging Accurate localization of the patient s scalp electrodes in 3-D space (digitization of electrode positions) Accurate source imaging algorithms Depiction of source imaging results on the individual patient s actual MRI brain images

14 Source Imaging of Eloquent Cortex in Epilepsy Pre-processing Co-registration Forw ard solution calculations Fitting & statistical analysis Segmentation Triangulation

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16 Source Imaging of Eloquent Cortex in Epilepsy

17 Source Imaging of Eloquent Cortex in Epilepsy Somatosensory Evoked Potential Locations (21-23ms)

18 Source Imaging of Eloquent Cortex in Epilepsy Table

19 Source Imaging of Eloquent Cortex in Epilepsy 44 hemispheres in 25 patients with epilepsy Type 1. Normal (15) Type 2. Central structural lesion (16) Type 3. No lesion, central EEG discharges (8) Type 4. Lesion or discharges outside central reg.(5)

20 Source Imaging of Eloquent Cortex in Epilepsy MEG PoC C PrC Total Dist.mm Type to 10 Type to 11 Type to 5 Type to 9 EEG PoC C PC Total Dist.mm Type to 17 Type to 8 Type to 9 Type to 12 PoC=Post-central C=Central PrC=Pre-central

21 No significant difference between EEG and MEG (33 channel vs 128) EEG detected N20/P30 in 3 hemispheres with central lesions/discharges where MEG could not N20 dipoles had a more radial orientation in these cases MEG added information in one hemisphere where EEG had poor signal to noise ratio, but potentials were still detectable (Type 2 hemis.) Value of combining modalities where central lesions/dysfunction exist

22 Houze et al. Human Brain Mapping 2011

23 Kakigi R et al: Progress in Neurobiology 2000

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25 Low frequency cut off 30Hz

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28 Conclusions Source imaging of eloquent cortex is best validated by study of the median N20/P20 response Multi-modal validation studies against the gold standard of cortical stimulation are currently lacking Reliable source imaging of hard-wired eloquent cortex will in turn validate source imaging of epileptiform abnormalities

29 Mehdi Hamaneh PhD Kitti Kaiboriboon MD John Turnbull PhD Hans Lüders MD PhD Farhad Kaffashi PhD Dan Dimitriu MD Kenneth Loparo PhD Joel Freitas MD Supported by: The Epilepsy Foundation The Coulter Foundation