[Classification of epileptogenic cerebral malformations: guide to understand the present conditions]

For dozens of years, a variety of pathological findings have been revealed through previous observations on surgically resected lesions from patients with intractable epilepsy, including excessive number of neurons in the molecular layer of cortices, unexpected existence of white matter neurons, and persistent columnar structure. These findings have sometimes been referred to as microdysgenesis (MD) or mild malformation of cortical development (mMCD), which is defined as microscopic abnormalities of brain formations with no macroscopical and neuroradiological findings. Taylor et al. (1971) described surgical cases with giant neurons and bizarre, grotesque cells as "focal dysplasia of the cerebral cortices with epilepsy." Since 1997, such malformations have subsequently been referred to as focal cortical dysplasia (FCD), in Greenfield's Neuropathology. Since early 2000, the definition of FCD has gradually been given a broader interpretation than the case described by Taylor et al., as shown in Palmini's classification (2004) or the newest classification (2011) proposed by the Neuropathology Task Force of the International League Against Epilepsy (ILAE). The ILAE classification describes 3 types of disease: Type I, Type II, and Type III. Type I is equivalent to some, but not all, pathological phenotypes of MD or mMCD. Type II is Taylor's FCD alone. Type III, which was not included in Palmini's classification, merges brain malformation and other pathological findings. However, the reproducibility of pathological diagnosis by using the ILAE classification was low, except for Type IIb. Hence, future studies are necessary to provide further reliable criteria for the pathological diagnosis of epilepsy patients.