Focal malformations of cortical development.

Abstract

Malformations of cortical development (MCDs) represent a heterogeneous group of disorders characterized by abnormal cortical and glial proliferation, neuronal migration, and cortical organization. Advances in neuroimaging have allowed for the growing recognition of a variety of developmental lesions associated with focal seizures. MCDs were present in 68% of infants and in 26% of children and adolescents with medically refractory epilepsy in recent surgical series.1,2⇓ In 1971, Taylor and Falconer3 described distinctive histopathologic findings in lobectomy specimens from 10 patients with epilepsy. Although the tissue appeared normal on gross examination, microscopically, cortical lamination was disrupted and large, and bizarre neurons were scattered randomly throughout the cortex and white matter. Large, distorted, round cells with clear, multiple nuclei and opalescent cytoplasm, known as balloon cells, were found in the deeper cortical layers and subjacent white matter. These histopathologic findings are referred to as focal cortical dysplasia–Taylor type (FCD-T). Although these pathologic changes were reminiscent of tuberous sclerosis (TS), no patients exhibited clinical or radiologic features of that disorder. FCD now is known to encompass a spectrum of pathologic changes from mild cortical disruption to more severe patterns of cortical dyslamination with large bizarre neurons, balloon cells, and astrocytosis.4 Tassi et al.5 recently differentiated FCD into three histopathologic subgroups and found notable differences in terms of their clinical, EEG, and imaging characteristics. In patients with FDC-T, seizure frequency was higher (nearly 100 seizures per month), and the epileptogenic zone was primarily extratemporal compared with patients with architectural dysplasia characterized by abnormal cortical lamination and ectopic neurons in white matter that were located primarily in the temporal lobe and associated with lower seizure frequency (average daily frequency >1).5 Those with cytoarchitectural dysplasia characterized by altered cortical lamination and giant neurofilament-enriched neurons had a seizure frequency exceeding that of …