Focal cortical dysplasias in eloquent cortex: Functional characteristics and correlation with MRI and histopathologic changes

Purpose: Focal cortical dysplasia (CD) is increasingly recognized as a common pathologic substrate of medically intractable epilepsy. As these lesions are often localized in the frontal lobe (therefore in potentially eloquent cortex), an understanding of the functional status of the involved region(s) and of its anatomic and pathologic correlates is of prime importance. The purpose of this study is to assess the function of focal CD in relation to magnetic resonance imaging (MRI) and histopathologic features. Methods: Eight patients operated on for medically intractable epilepsy with histologically proven focal CD involving putative eloquent cortex in the frontal lobe (perirolandic and Broca's areas) were included in the study. Functional regions (motor and language) and epileptogenic areas were assessed by extraoperative clectrocorticographic recording and electrical cortical mapping. Cortical functions were correlated with the extent of epileptogenicity on electrocorticographic recordings, MRI features, and histologic characteristics. Results: Language or motor areas were colocalized with epileptogenic regions (n = 6 of 8, 75%), but were not mapped in regions of increased signal on fluid-attenuated inversion recovery (FLAIR) MRI (when they were identified) on preoperative MRI (n = 5 of 5, 100%). Histologically, balloon cells were almost exclusively found in nonfunctional regions with FLAIR MRI abnormalities. When resected, regions of motor cortex were characterized by cortical dyslamination, columnar disorganization, and dysmorphic neurons, but were devoid of balloon cells. Conclusions: We found an absence of language or motor functions in perirolandic and Broca's areas that showed decreased epileptogenicity, histopathological evidence of CD with balloon cells and FLAIR MRI signal increase. Language and motor functions were present in epileptogenic and dysplastic areas with no balloon cells and no FLAIR signal abnormalities. These findings have implications on options for epilepsy surgery in patients with CD.