[Prognostic value of electrocorticography in temporal lobe epilepsy: patterns of relationing mesial and neocortical...

Electrocorticography (ECoG) monitoring in temporal lobe epilepsy (TLE) has been employed since the 40 s as a means to delineate surgical removal especially in lesional epilepsy, to reduce resection size and decrease cognitive sequelae (memory, naming). However in recent years, ECoG has been claimed to lack indications and prognostic value in cases of non lesional TLE. On the grounds of the pathophysiological relationship between mesial structures and neocortex (through propagation pathways) we have suggested a classification of ECoG activity patterns regarding the activities simultaneously recorded in mesial and neocortical grids.

Two experienced neurophysiologists (over 200 ECoG performed) have independently reviewed the recordings (including video EEG monitoring with foramen ovale electrodes) of 33 consecutive (28 non-lesional) TLE patients with the major criterion of a leading activity in mesial or neocortical areas, and related the results to the clinical course.

As a result we identified five patterns: I. Pure mesial; II. Mesial with neocortial-related activity; III. Non-related mesial and neocortical activities; IV. Neocortical preponderance (although some mesial unrelated discharges may be seen), and V. Neocortical origin. In all 33, a tailored, ECpG-guided two-steps resection was performed. Surgical success significantly (c2 test) associated with patterns I, II and IV. Pattern V precluded a good outcome.

ECoG reflects the state of pathological involvement of neocortex and mesial structures. An expertise approach, although brief in time (20-30 min), may either lead to preservation of relevant tissue (patterns I, II) and to establish a prognosis on the grounds of the initial epileptogenic activity.