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Background
Seizure refers to the clinical manifestations of transient abnormally excessive brain electric activity, and epilepsy is defined as a chronic disease/syndrome characterized by recurring seizure activities with neurological, cognitive, and social consequences. Neuroimaging plays a critical role in management of patients with seizure and epilepsy. Various modalities including CT, MRI, PET/SPECT are commonly used. CT is the modality of choice for first time seizure to exclude acute findings such as intracranial hemorrhage, mass, and hydrocephalus. MRI is essential in evaluating patients with drug-resistant epilepsy to detect structural lesions that can be surgically resected to achieve seizure freedom.

Educational Goals / Teaching Points
After reviewing the exhibit, the participants should be able to describe the classification of epilepsy, become familiar with the protocol to evaluate drug-resistant, intractable epilepsy, understand the anatomy of mesial temporal lobe and hippocampus, and recognize MRI appearance of common and uncommon epileptogenic lesions.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Epilepsy can be classified into mesial temporal lobe epilepsy (MTLE) and neocortical epilepsy that can involve the neocortex of frontal, temporal, parietal, occipital lobe and insula. Hippocampus is the anatomy substrate for MTLE. Hippocampus can be anatomically divided into head, body and tail. It consists of hippocampal proper, dentate gyrus and subiculum and continues with parahippocampal gyrus. The MRI appearance of the following epileptogenic lesions will be reviewed using an image rich approach. Hippocampal sclerosis (HS) - focal cortical dysplasia (FCD). Other malformations of cortical development (MCD) - polymicrogyria (PMG), heterotopia, schizencephaly and hemimegalencephaly. Epileptogenic tumors. Vascular lesions (arteriovenous malformation, cavernous malformation). Encephalocele. Autoimmune encephalitis.

Conclusion
Many epileptogenic structural defects are subtle on MRI. Having an optimized MRI protocol is essential to detect these lesions and guide treatment. It is critical for radiologists to be familiar with the imaging appearance of these lesions and have a structured approach. Correlation with semiology, electroencephalogram and PET/SPECT findings improve the detection of subtle lesions.