The role of the insular cortex in temporal lobe epilepsy

Abstract

The role of the insular cortex in the genesis of temporal lobe epileptic (TLE) seizures has been investigated in 21 patients with drug‐refractory TLE using chronic depth stereotactic recordings of the insular cortex activity and video recordings of ictal symptoms during 81 spontaneous electroclinical seizures. All of the recorded seizures were found to invade the insula, most often after a relay in the ipsilateral hippocampus (19/21 patients). However, 2 patients had seizures that originated in the insular cortex itself. Ictal symptoms associated with the insular discharges were similar to those usually attributed to mesial temporal lobe seizures, so that scalp video‐electroencephalographic monitoring does not permit making any difference between ictal symptoms of temporo‐mesial and insular discharges. A favorable outcome was obtained after a temporal cortectomy sparing the insular cortex in 15 of 17 operated patients. Seizures propagating to the insular cortex were found to be fully controlled by surgery, whereas those originating in the insular cortex persisted after temporal cortectomy. The fact that seizures originating in the insular cortex are not influenced by temporal lobectomy is likely to explain some of the failures of this surgical procedure in TLE. Ann Neurol 2000;48:614–623

Localization of Abnormal Discharges Causing Insular Epilepsy by Magnetoencephalography

“…This spike type, also known to be common in TLE , may represent temporal lobe activity propagated from the insula. The insular cortex is known to have dense neuronal connections to the temporal cortex (Penfield and Faulk 1955;Augustine 1996;Isnard et al 2000;Ostrowsky et al 2000). Consequently, insular epilepsy and TLE are likely to have common clinical features as well as similar scalp EEG distribution and MEG localization of E/ M-spikes.…”

“…Scalp EEG localizes the epileptic discharges of both TLE and insular epilepsy in the anterior temporal lobe. Therefore, insular epilepsy may be misdiagnosed as TLE, unless a structural lesion is identified within the insula (Roper et al 1993;Cukiert et al 1998) or epileptic discharge is detected within the insula by invasive EEG monitoring using intracranial electrodes (Roper et al 1993;Isnard et al 2000).…”

Epileptiform synchronization in the rat insular and perirhinal cortices in vitro

“…Importantly, in two cases the IC initiated ictal activity which then spread to other temporal lobe structures to mimic a typical temporal lobe seizure. Perhaps not surprisingly, upon temporal lobe resection (which leaves the IG intact), the two patients with IG ictal foci were not remedied of their seizures (Isnard et al, 2000), white nearly ail other patients were.…”

Metabolism is Normal in Astrocytes in Chronically Epileptic Rats: A 13C NMR Study of Neuronal—Glial Interactions in a Model of Temporal Lobe Epilepsy

“…Epileptogenic activity is usually not restricted to the hippocampus but spreads to other brain regions, particularly to the temporal lobes (Adam et al, 1994;Isnard et al, 2000). Thus, it is not surprising that metabolites in the cerebral cortex were also affected in epileptic Li-pilo rats.…”