Paradoxical ictal EEG lateralization in children with unilateral encephaloclastic lesions

Background. Describe an ictal EEG pattern of paradoxical lateralization in children with unilateral encephaloclastic hemispheric lesion acquired early in life. Methods. Of 68 children who underwent hemispherectomy during 2003-2005, scalp video-EEG and brain MRI of six children with an ictal scalp EEG pattern discordant to the clinical and imaging data were reanalyzed. Medical charts were reviewed for clinical findings and seizure outcome. Results. Age of seizure onset was 1 day-4 years. The destructive MRI lesion was an ischemic stroke in 2, a post-infectious encephalomalacia in 2, and a perinatal trauma and hemiconvulsive-hemiplegic syndrome in one patient each. Ictal EEG pattern was characterized by prominent ictal rhythms with either 3-7 Hz spike and wave complexes or beta frequency sharp waves (paroxysmal fast) over the unaffected (contralesional) hemisphere. Scalp video-EEG was discordant, however, other findings of motor deficits (hemiparesis; five severe, one mild), seizure semiology (4/6), interictal EEG abnormalities (3/6), and unilateral burden of MRI lesion guided the decision for hemispherectomy. After 12-39 months of post-surgery follow up, five of six patients were seizure free and one has brief staring spells. Conclusion. We describe a paradoxical lateralization of the EEG to the "good" hemisphere in children with unihemispheric encephaloclastic lesions. This EEG pattern is compatible with seizure free outcome after surgery, provided other clinical findings and tests are concordant with origin from the abnormal hemisphere.