Intrinsic epileptogenicity of cortical tubers revealed by intracranial EEG monitoring.

OBJECTIVE: We sought to identify intracranial EEG patterns characteristic of epileptogenic tubers and to understand the contribution of perituberal cortex.
METHODS: Twenty-three intracranial EEG monitoring studies were reviewed from 17 children aged 1.3-7.7 years with tuberous sclerosis complex and intractable multifocal epilepsy, 14 with a history of epileptic spasms. Interictal epileptiform discharges and ictal rhythms for 60 electroclinically distinct seizures (EDS) were analyzed in relation to 162 sampled tubers.
RESULTS: Localized, tuber-related, ictal rhythms were seen in 49/60 EDS, most commonly as low-voltage fast activity recruiting to rhythmic spiking, then diffuse slowing or bursts of ripple range activity. Ictal onset in localized EDS involved only tubers in 57% and tubers with perituberal cortex in 31%. Ictal fast ripples (FR) noted at seizure onset in 15/38 localized EDS were confined to tubers in 73% and involved tuber with perituberal cortex in 27%. Intraictal activation occurred during seizure propagation in 19 localized EDS, being to tubers in 63% and to tubers with perituberal cortex in 37%; 63% of activated tubers generated independent EDS. Trains of periodic sharp waves on an attenuated background were seen interictally at 36/162 tubers, with 67% of those tubers generating EDS (p = 0.0001). Interictal FR, when present, involved tubers more commonly than perituberal cortex but were not associated with EDS.
CONCLUSION: The study demonstrates interictal and ictal intracranial EEG findings characteristic of epileptogenic tubers, suggests that tubers play a greater role in seizure genesis than perituberal cortex, and suggests tuberectomy may be a sufficient surgical approach in a number of patients.