We report an 18 year-old male with a hemispheric large porencephaly who demonstrated symptomaticWest syndrome and then developed into Lennox-Gastaut syndrome. An electroencephalogram showed anasymmetrical high voltage slow spike and wave discharges only on the right side as a side of porencephalichemisphere. Interestingly, on the opposite side of the porencephalic hemisphere, an electroencephalogramshowed a low amplitude background activity in general. In this unique features both right side hemisphericporencephaly and asymmetric high voltage slow spike and waves due to Lennox-Gastaut syndrome, theporencephalic hemisphere due to cortical parenchymal loss may be more affected than the other hemisphereby epileptiform discharge in this patient
