Abstracts

Rationale: Parahippocampal epilepsy (PHE) is form of partial epilepsy arising from the parahippocampal gyrus (PHG). Identification of the epileptogenic lesions in the PHG may not be appreciated if the lesions are subtle and proper imaging protocol is not done. We examine the electroclinical and imaging features that suggest that epilepsy may arise from the PHG. Methods: Seven patients with intractable lesional PHE were reviewed. The results of video EEG monitoring, intracranial EEG studies when done, PET, SPECT, neuropsychological testing and MRI brain scans were analyzed for distinctive features. All patients had surgery and pathological reports were reviewed. Results: Of seven patients ultimately localized unilaterally to the PHG, four mimicked either frontal lobe epilepsy or bitemporal epilepsy, five were initially thought to be MR negative and only two had epilepsy typical of a unilateral origin in the mesial temporal region. Two patients had obvious focal lesions and underwent leisonectomy. None of the MRI scans showed hippocampal sclerosis. Five cases had subtle but distinctive MRI abnormalities in the PHG that pathologically showed dysplastic features. Of the five with this subtle parahippocampal abnormality four have had successful surgery with no seizures or auras only, with minimum of two years follow up. The follow up in one patient has been very short to access outcome. Conclusions: The diagnosis of unilateral PHE depends critically on recognition of subtle imaging findings as it is an electroclinical mimic. We recommend that in patients with lesion negative partial epilepsy, or bitemporal seizures, subtle parahippocampal abnormalities should be carefully excluded. Recognizing the MRI findings of an abnormal PHG led to successful surgery despite apparently incongruent electroclincal features. Parahippocampal epilepsy may also be an under-recognized cause of surgical failure for seizure outcome.