Focal cortical dysplasia: prevalence, clinical presentation and epilepsy in children and adults.

Focal cortical dysplasias (FCD) are defined as circumscribed malformations of cortical development. They result from an impairment of neuronal proliferation, migration and differentiation. In the diagnosis of focal epilepsy FCD prevalence ranges between 5% and 25%, depending on patient collective and imaging techniques. Several 'cryptogenic' epilepsies may be caused by FCD but have not been diagnosed because of the lack of high-quality magnetic resonance imaging assessment. Retrospective analysis of patients who have undergone epilepsy surgery can be biased because of the fact that they represent a mere subset of potential FCD diagnoses. Epilepsy typically manifests within the first years of life, but has been documented up to the age of 60 years. Cognitive impairment commonly accompanies early onset. Epilepsy is often refractory to antiepileptic drug (AED) treatment. Clinical observations and pathophysiological findings illustrate intrinsic epileptogenicity. Upregulation of drug transporter proteins has been found in FCD tissue. There is no specific drug treatment in FCD, as any AED used in focal epilepsy could prove effective. A sequential AED therapy should be designed individually and take side effects as well as developmental progresses into consideration. Fifty to sixty-five percent of FCD patients are rendered seizure-free after surgery. Presurgical evaluation should be initiated after two unsuccessful AED trials. Both risks and potential benefits regarding seizure control and developmental impairment need to be considered on an individual basis when deciding between surgical intervention and conservative treatment. Current knowledge on epilepsy course and psychomotor development in FCD is limited in the absence of qualified long-term studies combining imaging with cognitive evaluation.