Histopathologic findings of malformations of cortical development in an epilepsy surgery cohort

Context. - Malformations of cortical development (MCDs) are an important cause of pharmacoresistent epilepsy and are frequently diagnosed in surgical pathology. The lack of uniform tissue processing and standard histopathologic nomenclature to describe MCDs has resulted in diagnostic ambiguity. Objective. - To describe the immunohistochemical findings of MCDs from a relatively large surgical epilepsy cohort and incorporate terminology that more adequately reflects the histopathologic findings into a contemporary classification of MCD. Design. - Utilizing the Mayo Clinic Rochester Surgical Pathology Database and patient records, 53 patients with previous intractable epilepsy and a known malformation of cortical development were identified. All of the cohort's paraffin embedded surgical specimens were resectioned and stained with hematoxylin-eosin, Luxol fast blue/cresyl violet, neurofilament protein, and glial fibrillary acidic protein. Each specimen was reviewed histologically and categorized according to a proposed focal MCD classification scheme that substitutes cytoarchitectural dysmorphism for cortical dysplasia and architectural disorganization for microdysgenesis. Results. - An MCD was recognized in 49 patients and grouped into 1 of the following 4 categories: (1) cytoarchitectural dysmorphism with balloon cells (n = 19), (2) cytoarchitectural dysmorphism without balloon cells (n = 12), (3) architectural disorganization (n = 8), or (4) polymicrogyria (n = 9). Conclusions. - The histopathologic features of focal MCD in a large epilepsy surgical cohort by using practical immunohistochemistry and a contemporary MCD classification scheme are described. It is proposed that the term focal cortical dysplasia be renamed as focal malformations of cortical development.