Radiological diagnosis in epilepsy

Abstract

To communicate the experience in the neuroradiological evaluation of epilepsy gathered in 13 years since the introduction of MRI in this field and to present typical MRI and CT features and appropriate examination techniques for the most frequent epileptogenic structural brain abnormalities. Typical signal and density characteristics of hippocampal sclerosis, glioneural tumors and cortical dysplasia, migration- and gyration-abnormalities, and vascular and posttraumatic lesions are analysed. Hippocampal sclerosis, the most frequent cause of focal epilepsy, can be detected with 90-98% sensitivity by visual analysis and quantitative signal and volume measurement of the hippocampi in high-resolution coronal T2-weighted MR images. Benign tumors, such as gangliogliomas and dysembryoplastic neuoepithelial tumors (DNT), as well as cortical dysplasias are frequently composed of cystic and solid parts, which may show calcification, but never edema. Blood-brain-barrier disruption as seen in approximately 40% of the benign tumors are the only feature that allows to differentiate them from non-neoplastic dysplasias. In rare cases of totally calcified lesions. CT may be the only diagnostic imaging modality. Proton-density-weighted or FLAIR imaging is essential for the detection of small solid cortical lesion components, because they provide sufficient contrast with adjacent CSF. T1-weighted inversion recovery images are most sensitive for the detection of migration and gyration abnormalities. The depiction of calcified lesions and hemosiderin deposits after trauma is most efficient with T2* weighted gradient echo sequences. With further rapid improvement of high resolution MRI techniques, the near future will probably show that nearly 100% of focal epilepsies are caused by structural brain abnormalities. With refined imaging techniques applied, the sensitivity of neuroradiological evaluation is 90% at present. Therefore presurgical MRI plays a key role in epilepsy surgery.