Clinical Characteristics of Focal Cortical Dysplasia: Correlation with Pathological Subtypes Peter Widdess-Walsh1, Richard Prayson2, William Bingaman3, Imad Najm1 Department of Neurology1, Anatomic Pathology2, and Neurosurgery3 Cleveland Clinic Foundation. Abstract: Purpose: Focal cortical dysplasia (CD) is a common cause of pharmacoresistant epilepsy that is amenable to surgical resection. CD is due to abnormalities in neuronal migration, proliferation, and/or differentiation that result in distinct pathological subtypes, termed 1A, 1B, 2A, and 2B. In this study, we retrospectively reviewed and compared the electroclinical and imaging characteristics of the pathological subtypes of CD. Methods: We retrospectively reviewed patient data from epilepsy surgeries at the Cleveland Clinic Foundation between 1990 and 2002. Only those patients with the definite pathological diagnosis of isolated cortical dysplasia were included in the study (n=120). Thirty-seven patients with dual pathology (FCD with hippocampal sclerosis) were also analyzed separately. Patient demographics, risk factors, results of video-EEG evaluations, MRI findings, and postsurgical outcomes were reviewed and analyzed. Results: Balloon cell (BC) containing lesions were found in 25 patients (21%) and were mainly localized to the fronto-central area. Patients with BC containing CD had: earlier age of onset of epilepsy and pharmacoresistance, higher incidence of perinatal complications, more frequent seizures, more prominent FLAIR MRI abnormalities, more severe impairment in their neuropsychological function, required more invasive evaluations, and were operated on at a younger age. They showed a favorable postoperative seizure outcome, unless an invasive evaluation was required. Multivariate analysis of postoperative outcomes showed that the presence of balloon cells and a non- frontal location of the epileptogenic zone predicted a good outcome. Conclusions: BC containing cortical dysplasia may represent a distinct pathological and clinical entity. Correlative immunohistochemical studies of balloon cells provide insight into the underlying pathophysiological mechanisms of epileptogenesis and will be discussed.