The ictal onset zone: general principles, pitfalls, and caveats A Arzimanoglou and P Kahane
2008
What is the meaning of the term ‘clinical seizure’ By definition ‘the ictal onset zone’ refers to that region of the cortex at the origin of clinically detectable seizures. Such a definition indirectly leads to the question of how we define ‘subclinical seizures’. Are these ‘discharges’ considered as seizures or not? Such discharges, very similar in terms of morphology to what can be observed at the onset of a clinical seizure, are often observed without any clinical accompaniment. The occurrence of accompanying symptoms may vary according to the localization of the discharge and to its electrographic pattern. This is notably true in temporal lobe epilepsy, in which an ictal discharge can remain confined to the amygdala6 or to the hippocampus7, the most often without any associated signs. It has been shown that subclinical seizures may have a high localizing significance,8 even if the recordings of such ‘subclinical’ discharges do not exempt one from recording the fully developed electro-clinical seizures. In which case, the discharge at seizure onset may additionally involve other cortical structures, or cortical structures which are different from the area exhibiting ‘subclinical’ paroxysms (Figure 67.2).