Temporal lobe epilepsy with unilateral hippocampal sclerosis and contralateral temporal scalp seizure onset: report of four patients with "burned-out hippocampus"

Abstract

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 presurgical 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 necessary before one can affirm that patients with unilateral HS and scalp ictal EEG showing contralateral ictal onset may be operated without confirmation of the epileptogenic zone by invasive monitoring. In these patients, semi-invasive monitoring with FO electrodes might be an interesting alternative.

MRI characterization of temporal lobe epilepsy using rapidly measurable spatial indices with hemisphere asymmetries and gender features

“…Hippocampi in ipsilateral side to ictal onset are equally affected in both genders of epileptic patients diagnosed by ictal and/or interictal activity [29][30][31]. Male TLE patients are more susceptible to early appearance of seizure [29,30] and have greater chance of hippocampal atrophy at contralateral side when the ictal onset side is left in certain cases [30,32].…”

A medically refractory epilepsy case with discordant presurgical findings: The pitfall of burned‐out hippocampus

“…5 Thus, scalp-EEG findings occur in contralateral temporal lobe. 6,7 Hence it is currently not easy to solve this EZ lateralization challenge with non-invasive EEG recordings. Awareness of this phenomenon is important for a favorable surgical outcome, as up to 80% of burnedout hippocampus cases can be seizure-free.…”

“…Proposed explanation for this phenomenon is as follows: In atrophic hippocampus, neuronal loss is so severe that it cannot cause ipsilateral neocortical activation, yet ictal activity may spread to contralateral hippocampus and temporal neocortex via dorsal hippocampal commissure 5 . Thus, scalp‐EEG findings occur in contralateral temporal lobe 6,7 . Hence it is currently not easy to solve this EZ lateralization challenge with non‐invasive EEG recordings.…”