Stereoelectroencephalography in the presurgical evaluation of focal epilepsy in infancy and early childhood

Clinical article

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Object

The authors report on the use of stereoelectroencephalography (stereo-EEG) in the presurgical electroclinical evaluation of infants and very young children with focal drug-resistant epilepsy.

Methods

Fifteen patients (9 girls and 6 boys, mean age 34.1 ± 7.3 months, range 21–45 months), potentially candidates to receive surgical treatment for their focal drug-resistant epilepsy, were evaluated using stereo-EEG recording for a detailed definition of the epileptogenic zone. Stereoelectroencephalography was indicated because neuroradiological (brain MRI) and video-EEG data failed to adequately localize the epileptogenic zone. Stereotactic placement of multicontact intracerebral electrodes was preceded by the acquisition of all pertinent anatomical information from structural and functional MRI and from brain angiography, enabling the accurate targeting of desired structures through avascular trajectories. Stereoelectroencephalography monitoring attempted to record habitual seizures; electrical stimulations were performed to induce seizures and for the functional mapping of eloquent areas. Stereoelectroencephalography-guided microsurgery, when indicated, pointed to removal of the epileptogenic zone and seizure control.

Results

Brain MRI revealed an anatomical lesion in 13 patients (lobar in 2 cases, multilobar or hemispheric in 11 cases) and was unremarkable in 2 patients. One patient underwent 2 stereo-EEG studies. The arrangement of the intracerebral electrodes was unilateral in all but 1 case. One patient died the day following electrode placement due to massive brain edema and profound hyponatremia of undetermined cause. In 8 cases intracerebral electrical stimulations allowed mapping of functionally critical areas; in 3 other cases that received purposeful placement of electrodes in presumably eloquent areas, no functional response was obtained. Of the 14 patients who completed stereo-EEG monitoring, 1 was excluded from surgery for multifocality of seizures and 13 underwent operations. Postoperatively, 2 patients exhibited an anticipated, permanent motor deficit, 3 experienced a transient motor deficit, and 2 experienced transient worsening of a preexisting motor deficit. Three patients developed a permanent homonymous hemianopia after posterior resections. Histological analysis revealed cortical malformations in 10 cases. Of the 10 patients with a postoperative follow-up of at least 12 months, 6 (60%) were seizure-free (Engel Class Ia), 2 (20%) experienced a significant reduction of seizures (Engel Class II), and 2 (20%) were unchanged (Engel Class IV).

Conclusions

The present study indicates that stereo-EEG plays a prominent role in the presurgical evaluation of focal epilepsies also in the first years of life and that it may offer a surgical option in particularly complex cases that would have scarcely benefitted from further medical treatment. Results of stereo-EEG–guided resective surgery were excellent, with 80% of patients exhibiting a substantial improvement in seizures. In consideration of the potentially life-threatening risks of major intracranial surgery in this specific age group, the authors recommend reserving stereo-EEG evaluations for infants with realistic chances of benefiting from surgery.

Abbreviation used in this paper:EEG = electroencephalography.

Article Information

Address correspondence to: Massimo Cossu, M.D., Centro per la Chirurgia dell'Epilessia, Ospedale Niguarda, Pad. 16, Piazza Ospedale Maggiore 3, Milan 20162, Italy. email: massimo.cossu@ospedaleniguarda.it.

Please include this information when citing this paper: DOI: 10.3171/2011.12.PEDS11216.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    Case 11. a–c: Stereo-EEG exploration. Coverage with intracerebral electrodes included right frontal, rolandic, temporal, insular, and anterior parietal areas, with 2 sentinel electrodes sampling the left opercular-insular cortex. Brain cortical surface reconstruction of the lateral (a) and mesial (b) aspects of the right hemisphere and of the lateral aspect of the left hemisphere (c) were obtained from the 3D T1-weighted MRI structural images. Black circles and corresponding upper-case letters indicate the surface impact points of each intracerebral electrode. d–f: Blended images of 3D T1-weighted MRI and coregistered postimplantation volumetric CT, in which single contacts of several intracerebral electrodes are easily recognizable. In particular, the insular cortex of both hemispheres was sampled by several electrodes, placed along different intracerebral trajectories. g: Stereo-EEG recording of a spontaneous seizure (open bracket = left hemispheric derivations). The earliest electrical modifications at ictal onset occurred in the right suprasylvian operculum and in the ipsilateral insular cortex (traces highlighted by asterisks). Subsequent propagation to the right frontal, central, and inferoparietal areas and to the left operculum is also evident. h and i: Postoperative MRI scans obtained 6 months after surgery show resection of the right suprasylvian opercula and the insular cortex. No Engel class was assigned to this case due to the short postoperative follow-up duration.

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    Case 13. a and b: Inversion recovery T1-weighted MRI showing abnormal gyral arrangement and altered gray-white substance interface in the basal and dorsal aspect of the left occipital lobe. c and d: Stereo-EEG exploration. Coverage with intracerebral electrodes includes the left occipital, parietal, and temporal lobes, as well as the inferior portion of the rolandic cortex. Brain cortical surface reconstruction of the lateral (c) and mesial (d) aspects of the left hemisphere was obtained from the 3D T1-weighted MRI structural images. Black circles and corresponding upper-case letters indicate the surface impact points of each intracerebral electrode. e–h: Blended images of 3D T1-weighted MRI and coregistered postimplantation volumetric CT, in which single contacts of several intracerebral electrodes are easily recognizable. i: Stereo-EEG recording of a spontaneous seizure, showing that the earliest electrical modifications at ictal onset occur in the external contacts of the electrodes “V” and “O,” sampling the dorsolateral cortex of the middle occipital cortex (traces highlighted by asterisks).

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