A 59 year-old right-handed healthy female delayed epilepsy surgery recommendations for 6 years until her daughter-in-law restricted their grand-son's visitation for fear of "Nana's" seizures. Seizure onset was at 35 years of age with weekly focal seizures and rare convulsions. Onset began with an indescribable feeling and nausea prior to a stare, lip smacking, and motion arrest. Her exam was normal except for a right eye visual field deficit (VFD). High-resolution brain MRI and PET were normal. vEEG demonstrated regional T2/F8 sharp waves and 3 focal seizures demonstrated right temporal rhythmic ictal theta onset. Wada testing revealed left hemisphere dominance for language and bilateral memory function. Neuropthamology confirmed a large superior-lateral monocular deficit OD from prior retinal tear. Diffusion tensor imaging (DTI) was obtained to assess the white matter tracks/Meyer's loop prior to right ATL.
Figure: Anatomic T1 coronal imaging with (A) a 3-T high resolution brain MRI with epilepsy protocol and B Diffusion Tensor Imaging with symmetric white matter tracts in the temporal lobes with high FA (arrow) delineating the integrity of medial amygdalohippocampal gray in a patient with a VFD .
MRI remains the imaging modality of choice for anatomic abnormalities. High-field magnets (e.g. 3.0 T) are increasingly used during pre-surgical evaluation of drug-resistant focal epilepsy. Abnormalities are identified in 1/4th of normal 1.5 T scans though with surface coils up to 65% (especially cortical dysplasia) may yield differences (1). DTI measures white mater integrity by measuring the directional magnitude of water diffusion in 3-dimensional space (fractional anisotropy: FA). A preferred direction of water diffusion is seen if white matter fascicles have structural coherence (high FA) but low FA if poor structural organization allows random water diffusivity. Both the distance from Meyer’s loop to the tip of the temporal lobe and extent of the resection predicts VFDs following temporal resection (2). DTI tractography of the optic radiations contained in the white matter tracts were left intact in our patient with a right amygdalo-hippocampectomy resulting in seizure-freedom without new VFD after surgery.
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