Temporal Lobe Sclerosis Associated With Hippocampal Sclerosis in Temporal Lobe Epilepsy: Neuropathological Features

Abstract

Widespread changes involving neocortical as well as mesial temporal lobe structures can be present in patients with temporal lobe epilepsy (TLE) and hippocampal sclerosis (HS). The incidence, pathology and clinical significance of neocortical temporal lobe sclerosis (TLS) are not well characterized. We identified TLS in 30 out of 272 surgically treated cases of HS. TLS was defined by variable reduction of neurons from cortical layers II/III and laminar gliosis; it was typically accompanied by additional architectural abnormalities of layer II, i.e. abnormal neuronal orientation and aggregation. Quantitative analysis including tessellation methods for the distribution of layer II neurons supported these observations. In 40% of cases there was a gradient of TLS with more severe involvement towards the temporal pole, possibly signifying involvement of hippocampal projection pathways. There was a history of a febrile seizure as an initial precipitating injury in 73% of patients with TLS compared to 36% without TLS; no other clinical differences TLS and non-TLS cases were identified. TLS was not evident pre-operatively by neuroimaging. No obvious effect of TLS on seizure outcome was noted after temporal lobe resection; 73% became seizure-free at 2 year follow up. In conclusion, approximately 11% of surgically treated HS is accompanied by TLS. TLS is likely an acquired process with accompanying re-organizational dysplasia and an extension of mesial temporal sclerosis rather than a separate pathological entity.