Cortical dysplasia and extratemporal resections in epilepsy

Focal cortical dysplasias (FCDs) are malformed regions of cerebral cortex known to cause epilepsy in both children and adults. They are characterized primarily by neuropathology, which demonstrates disorders in lamination and neuronal morphology. Type 1 is characterized by dyslamination and altered neuronal morphology (hypertrophy, hypotrophy, and aberrant dendritic arborization). Type 2 is characterized by disorder of all laminae apart from layer 1 and neuronal dysmorphism. Balloon cells, multinuclear opalescent cells, are also characteristic of type 2. Type 3 occurs secondarily to a range of primary neocortical disorders. FCDs can be difficult to diagnose, as they can be microscopic and/or multifocal. With higher Tesla technology and advanced sequences, magnetic resonance imaging (MRI) has become a mainstay for the evaluation of focal cortical dysplasia. A range of imaging characteristics can aid diagnosis, including thickened cortical gray matter, blurred gray-white matter junction, regional T2 signal hyperintensity, focal hypoplasia, white matter atrophy, and transmantle dysplasia. Invasive techniques for evaluation and treatment include intracortical recording by depth or subdural electrodes and surgical resection. Surgical resection may result in seizure freedom in up to two-thirds of cases. Likelihood of seizure freedom after surgery is associated with extent of resection, which may be limited by the involvement of eloquent cortex or by inadequate preoperative identification of dysplastic tissue using MRI and physiological assessment.