Parahippocampal epilepsy with subtle dysplasia: A cause of "imaging negative" partial epilepsy.
OBJECTIVE
Lesion-negative refractory partial epilepsy is a major challenge in the assessment of patients for potential surgery. Finding a potential epileptogenic lesion simplifies assessment and is associated with good outcome. Here we describe imaging features of subtle parahippocampal dysplasia in five cases that were initially assessed as having imaging-negative frontal or temporal lobe epilepsy.


METHODS
We analyzed the clinical and imaging features of five patients with seizures from the parahippocampal region.


RESULTS
Five patients had subtle but distinctive magnetic resonance imaging (MRI) abnormalities in the parahippocampal gyrus. This was a unilateral signal abnormality in the parahippocampal white matter extending into gray matter on heavily T(1)- and T(2)-weighted images with relative preservation of the gray-white matter boundary on T(1)-weighted volume sequences. Only one of these patients had typical electroclinical unilateral temporal lobe epilepsy (TLE); one mimicked frontal lobe epilepsy, two showed bitemporal seizures, and one had unlocalized partial seizures. All have had surgery; four are seizure-free (one has occasional auras only, follow-up 6 months to 10 years), and one has a >50% seizure reduction. Histopathologic evaluation suggested dysplastic features in the surgical specimens in all.


CONCLUSIONS
In patients with lesion-negative partial epilepsy with frontal or temporal semiology, or in cases with apparent bitemporal seizures, subtle parahippocampal abnormalities should be carefully excluded. Recognizing the MRI findings of an abnormal parahippocampal gyrus can lead to successful surgery without invasive monitoring, despite apparently incongruent electroclinical features.
Pillay
Neelan
N
Brain Research Institute, Heidelberg Heights, Victoria, Australia. pillay@ucalgary.ca
Fabinyi
Gavin C A
GC
Myles
Terry S
TS
Fitt
Gregory J
GJ
Berkovic
Samuel F
SF
Jackson
Graeme D
GD
D000328:Adult; D018572:Disease-Free Survival; D004569:Electroencephalography; D018728:Entorhinal Cortex / Q000002:abnormalities / Q000473:pathology / Q000503:physiopathology; D004828:Epilepsies, Partial / Q000473:pathology / Q000503:physiopathology* / Q000601:surgery; D017034:Epilepsy, Frontal Lobe / Q000175:diagnosis; D004833:Epilepsy, Temporal Lobe / Q000175:diagnosis; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000706:statistics & numerical data*; D008297:Male; D054220:Malformations of Cortical Development / Q000175:diagnosis / Q000473:pathology / Q000503:physiopathology*; D008875:Middle Aged; D009483:Neuropsychological Tests; D020534:Parahippocampal Gyrus / Q000473:pathology / Q000503:physiopathology* / Q000601:surgery