Abstracts

Surgical selection is evolving to a point at which localization of the epileptogenic zone and eloquent functional cortex before any surgery is vital. In patients with intractable epilepsy associated with malformations of cortical development (MCD) in the rolandic regions, the presurgical evaluation is a challenge because unpredictable localization of the primary somatosensory and motor functions may exist. In a previous study using magnetoencephalography, patients with epileptic MCDs were found to have reorganization if the MCDs were due to an abnormal neuronal or glial proliferation (i.e. cortical dysplasia) but that was not the case in MCDs caused by abnormal cortical organization (i.e. polymicrgyria). In the present study we use MRS and fMRI respectively to verify these observations., Three patients with MCDs and intractable epilepsy localized to the central or rolandic areas were selected. The selection was made by MRI identification and anatomic localization of the MCDs. Patients also underwent standard presurgical evaluation for epilepsy surgery. In every patient, we used short echo-time 4 Tesla proton single voxel MRS (TE/TR 40/3200 ms) and fMRI (motor and sensory paradigms). The spectroscopic results for creatine and choline from MCD were compared as ratios to N-acetlyaspartate (Cr/NAA and Cho/NAA respectively) with data from control tissue regions. For somatosensory mapping, repetitive (block design) tactile stimulation was applied to each hand. For the motor mapping, patients performed self-paced motor tasks of both hands by opposing the thumb to each finger starting at the index and ending on the fifth digit. The position of the [quot]local maxima[quot] of activity was determined for all functional paradigms. A localization of either sensory or motor cortical function that was [gt]2 SD from the expected anatomic localization (obtained from controls) was considered aberrant or representative of reorganized function., One patient had unilateral polymicrogyria with schizencephaly , one had cortical dysplasia, and one had bilateral perisylvian polymicrogyria. The polymicrogyric tissues had comparable metabolic profile with homogeneous healthy cortical areas in healthy hemispheres, and the pattern of localization in fMRI was as expected in spite of the extensive malformations, when compared with healthy hemispheres (controls). This was not appreciated in the case of cortical dysplasia, even though the metabolic profile was normal, which could be related to the small number of controls., These preliminary MRSI- and fMRI-based findings indicate that polymicrogyric tissue behaves as healthy (non-MCD) cortical tissue while cortical dysplasia reorganizes the somatosensory and motor cortices. The results need to be expanded, as we collect information in other types of MCD., (Supported by PSI Foundation and The University of Western Ontario (JGB).)