ICTAL EEG CHANGES WITH CORPUS-CALLOSUM SECTION

Corpus collosum section diminishes but does not completely abolish sec ondary bilaterally synchronous interictal EEG discharges, yet often ca uses cessation of generalized seizures. The effects of corpus callosum section on ictal EEG patterns have not been described. We contrasted ictal EEG patterns before and after anterior callosotomy in 18 patient s and before and after total callosotomy in 10 patients. Bilaterally s ynchronous seizure onset was disrupted in 5 of 11 anterior section pat ients and 5 of 5 total section patients. Seven of 18 anterior section patients and 5 of 10 total section patients had more localized seizure onset after the procedure; localization to the frontal lobe was obser ved after anterior or total section, but only total section patients h ad newly demonstrated posterior locations of seizure onset. These data suggest that the mechanisms by which bilaterally synchronous interict al and ictal discharges are generated differ. Although brainstem or di encephalic structures may contribute to formation of interictal bilate ral synchrony, the corpus callosum may be the only pathway used in pro ducing apparent bilateral synchronous seizure onset in patients with s econdarily generalized seizures.