Temporal Lobe Epilepsy with Unilateral Hippocampal Sclerosis and Contralateral Temporal Scalp Seizure Onset: Report of Four Patients with “Burned-out Hippocampus”

Objectives: Patients with temporal lobe epilepsy (TLE) and unilateral severe hippocampal sclerosis (HS) may have contralateral temporal scalp ictal onset. This has recently been called “burned-out hippocampus”, which is believed to be a rare entity. In this study we report four patients with unilateral hippocampal sclerosis and contralateral ictal onset registered by scalp electrodes. We discuss the importance of such cases in pre-surgical evaluation of patients with TLE, as well as possible strategies used for evaluation of these particular cases. Patients and methods: We reviewed charts from all patients with TLE submitted to pre-surgical evaluation, which included high resolution MRI and prolonged video-electroencephalogram (video-EEG) monitoring with scalp and sphenoidal electrodes, during a three-year period (2002-2004). We looked for patients who only had seizures that were clearly contralateral in location to the atrophic hippocampus. Results: Four patients fulfilled the criteria above. Two of these patients had semi-invasive video-EEG monitoring with foramen ovale (FO) electrodes, which revealed seizures originating from the temporal lobe with the atrophic hippocampus, hence confirming false lateralization in the scalp-sphenoidal EEG. These patients were submitted to surgical treatment and had favorable prognosis after surgery. Conclusions: Burned-out hippocampus syndrome may not be as rare as it was previously believed. Further studies will be necessar