Structural epilepsies are conceptualized as having a distinct structural brain abnormality that has been demonstrated to be associated with a substantially increased risk of epilepsy in appropriately designed studies. The structural brain abnormality can be acquired (such as due to stroke, trauma or infection) or may be of genetic origin; however, as we currently understand it, the structural brain abnormality is a separate disorder interposed between the acquired or genetic defect and the epilepsy.
Magnetic resonance imaging (MRI) using a 1.5Tesla magnet is the minimum standard investigation for exclusion of a structural abnormality, although it is acknowledged that MRI may not be available in resource-poor settings. When a MRI study is performed, it is important to perform epilepsy-directed protocols that allow careful scrutiny for specific acquired abnormalities (e.g. hippocampal sclerosis) and subtle malformations of cortical development such as focal cortical dysplasia. Imaging with 3Tesla or higher strength, and the use of advanced software analysis methods, may assist with the identification of structural abnormalities not obvious on routine MRI. Interictal and ictal EEG together with complementary functional neuroimaging studies such as PET, SPECT and MEG, where available, may assist by directing attention to a particular brain region allowing a subtle abnormality to be identified. In young children imaged under the age of 2 years, subtle abnormalities may not be appreciated and repeat imaging may be required after myelination is complete.
Common structural brain abnormalities associated with epilepsy are presented in this section of EpilepsyDiagnosis.org: