Neuropathology of pediatric epilepsy

The preoperative study of patients who are candidates for epilepsy surgery often classifies their epileptic foci as "lesional" or "non-lesional" based upon evidence from neuroimaging. Many lesions not detected by MRI are found by microscopic examination of the resected tissue. Advances have been made in neuropathological techniques to study resected brain tissue and to specify the types of focal cortical dysgeneses and other lesions by extending microscopic findings by applying immunocytochemical markers that identify specific types and distributions of neurons and glial cells that denote tissue architecture. There may be etiological differences between focal and extensive cortical dysplasias involving many gyri or entire lobes of cerebral cortex. Of additional importance in pediatric brain resections is that these modern techniques also denote cellular maturation and can identify abnormal cells with mixed lineage. α-B-crystallin can serve as a metabolic tissue marker of epileptic activity, regardless of the presence or absence of a "structural" lesion by MRI or by conventional histopathology. Satellitosis may contribute to epileptogenic neurons and later to death of those neurons. The classification of malformations of the brain is a process requiring continuous updates that include genetics, neuroimaging, and neuropathology as new data emerge, but should not be exclusive to one region of the brain, such as cerebral cortex or cerebellum. Standardization in neuropathological terminology enhances scientific communication. The ILAE recently published a useful consensus classification of focal cortical dysplasias that is flexible to enable future revisions and changes as new data become available.