Abstracts

Rationale: Functional reorganization of cerebral cortex occurs in subjects with malformations of cortical development (MCD). In some MCD, functional MRI (fMRI) shows blood oxygen level-dependent (BOLD) activation in malformed cortices, suggesting their functional integrity. This raises concerns about post-surgical deficits in patients with MCD and medically refractory epilepsy. We aimed to assess functional integrity of MCD in language neural network in patients with epilepsy and MCD by use of fMRI. Methods: Forty-six patients (26w/20m) aged 15-73 years (mean 33.5 years) with MCD and epilepsy were selected at the Department of Neurology and Neurosurgery, Medical University Innsbruck, Austria. All subjects underwent MRI (1.5-T) and fMRI. Single-subject image analysis was performed with statistical parametric mapping (SPM5). MCD diagnosis was based on MRI and classified according to Barkovich et al., 2005. MCD were located either in vicinity of language cortex - Broca's and Wernicke's areas or subependymally along lateral ventricles. Patients had to generate silently words staring with letters K and S and words in categories Animals and Tools . Patients were tested for the ability to perform the task before scanning. All patients had been seizure free for at least 48 hours prior to fMRI study. Subsequently, seven patients underwent epilepsy surgery. Histological classification of focal cortical dysplasia (FCD) was based on nomenclature proposed by Palmini et al. 2004. Results: Fifteen patients had periventricular nodular heterotopias (PNH); nine- polymicrogyria (PMG); five- FCD type II; seven- FCD type I; six- tuberous sclerosis (TS); one- dysembryoplastic neuroepithelial tumour; one - hemimegalencephaly; one - subcortical laminar heterotopia (SLH); and one - TS with PMG. Majority of patients (44/46) had focal epilepsy; 32/46 (70%) were pharmacoresistant. Mean age at seizure onset was 15 years (range 1-61); mean epilepsy duration for time of fMRI- 12.5 years (range 1-58). Shift of BOLD activation from MCD affecting language cortex was observed only in patients with FCD type II (3/5) and TS (2/6). Malformed cortices involving language cortex harboured BOLD activation in patients with FCD type I (6/7), PMG (4/10) and SLH (1/2). In PNH situated along lateral ventricles BOLD activation was not observed. In four patients no BOLD activation was registered. Neither shift of BOLD activation from affected language cortices nor their BOLD activation, were influenced by age at seizure onset, seizure frequency during the first year of epilepsy, epilepsy duration, seizure outcome or handedness. Bilateral BOLD activation of language cortices was observed in 24/46 (52%) patients (either unaffected or dysplastic) irrespective of handedness, age at seizure onset, laterality or type of MCD. Conclusions: In patients with MCD affecting language cortices, word generation task fMRI suggests functional integration of MCD due to abnormal neuronal migration (SLH) or organization (FCD type I, PMG) and shift of function from MCD due to abnormal neuronal proliferation/apoptosis (FCD type II, TS).