Pathology in Epilepsy Surgery

Abstract

It may be postulated that every focal epilepsy is based on structural abnormalities of the brain. In fact, since the description of Ammon’s horn sclerosis in 1880 by Sommer, histopathological analysis of specimens obtained from epilepsy surgery revealed a large amount of lesions including hippocampal sclerosis, malformative, neoplastic, ischemic, and traumatic lesions, as well as cerebrovascular and infectious diseases. The data of the European Epilepsy Brain Bank (EEBB) comprising specimens of 9523 patients (4944 men, 4579 women; 6900 adults, 2623 children) who underwent resective surgery for drug-resistant seizures in 36 centers of 12 European countries over 25 years have been published by Blumcke et al. in 2017. Overall, the most common categories were hippocampal sclerosis (HS) as found in 36.4% of the patients (88.7% of cases were adults), tumors (mainly gangliogliomas) detected in 23.6%, and malformations of cortical development (MCD) as observed in 19.8% of patients (focal cortical dysplasia was the most common type, 52.7% of cases were children). No histopathological diagnosis could be established for 7.7% of the patients. The ten most frequent histopathological diagnoses accounted for 86.7% of cases. Overall, seizure-free outcome at 1-year follow-up was achieved in 61.4% of patients with HS, 68.4% with tumors, 57.6% with MCD, and in 50.2% without specific pathological findings. Advances in neuropathological diagnosis and classification of epileptogenic brain lesions contribute to the understanding of epileptogenesis and are helpful for clinical correlation, outcome stratification, and patient care. The relatively high rate of seizure-free outcome in patients without specific pathological findings rises questions as to the classical concept of epileptogenesis based on specific structural abnormalities indicating successful surgical interruption of functional epileptogenic networks.