Occurrence of bilaterally independent epileptic spasms after a corpus callosotomy in West syndrome.

We report a patient with intractable West syndrome whose epileptic spasms (ESs) were initially bilaterally synchronous, as is typical; after a complete corpus callosotomy, however, bilaterally independent ESs originated in either hemisphere. Activity of probable cortical origin associated with ESs was detected by observing ictal gamma oscillations. Brain MRI revealed no structural abnormality before surgery. This case suggests that ESs with a hemispheric origin may appear generalized because of synchronizing effects in the corpus callosum in some patients.