Montreal Neurological Institute, 3801 rue Université, Montreal, Quebec H3A 2BA, Canada.
It is now half a century since temporal lobe epilepsy was first identified and recognized as the most common type of refractory, focal epilepsy. The neuronal systems responsible for the seizures which characterize this form of epilepsy fail to respond to currently available anti-epileptic drugs in fully one third of cases although the exact reasons for this non-responsiveness are not yet understood. In contrast, the discharge responsible for propagation and secondary generalization is usually controllable with drugs. While certain issues related to the anatomical background of temporal lobe epilepsy remain controversial, modern imaging modalities notably MRI are proving to be powerful tools in this field, making it possible to visualize and make accurate measurements of all the various structures of the temporal lobe, and to correlate the results with clinical data and surgical outcomes. On the basis of the region in which the seizures originate, it has been proposed that two distinct forms of temporal lobe epilepsy exist, namely medial and lateral. However, distinguishing these two forms on purely clinical criteria remains difficult. Earlier analyses carried out by Murray Falconer and his team at King's Maudsley Hospital working with the neuropathological data of Nicholas Corsellis and Clive Bruton were already hinting at the existence of different types of temporal lobe epilepsy, the surgical outcomes of which are very different. This led Falconer to propose that only patients with evidence of hippocampal sclerosis were suitable candidates for surgery. The same work revealed the causative role of prior, prolonged febrile convulsions in the pathogenesis of mesial temporal sclerosis. Ever since, it has been clear that temporal lobe epilepsy is not a single, uniform pathological entity.