Abstracts

Rationale: Rationale: Malformations of cortical development (MCD) is an important cause of refractory epilepsy in children. Epilepsy surgery in MCD is challenging because the epileptogenic zone often extends beyond the MRI defined morphological abnormalities and, in some situations, MRI can be normal. In MRI-negative cases, positron emission tomography (PET) can be helpful in identifying MCD. We analyzed the clinical, neuroimaging features, pathologic findings and surgical outcome in 32 children with MCD and intractable epilepsy who underwent epilepsy surgery (2001-2007) in Children’s Hospital of Michigan, Detroit. Patients with tuberous sclerosis were not included.Methods: Methods: Thirty-two children (age at surgery: 3 mo to 20 yrs; 19 boys) underwent presurgical evaluation including MRI, video-EEG and glucose metabolism PET. 18 patients also underwent PET scanning using [11C]-flumazenil (FMZ) and/or alpha[11C]methyl-l-tryptophan (AMT). Results: Results: Mean age at seizure onset was 2.1 yrs (range: in-utero to 8 yrs). All patients had focal seizures with or without secondary generalization. 3 had associated myoclonic and atonic seizures. 12 patients also had epileptic spasms; 2/12 had asymmetric spasms. In 7 patients (21%), MRI was normal whereas glucose PET scan showed functional abnormalities concordant with the presumed epileptic lobe defined by video-EEG and confirmed by electrocorticography (ECOG). Moreover, in 10 of the 25 MRI-positive cases, glucose PET abnormalities extended beyond the MRI defined lesion. In 6 of these 10 cases, these PET abnormalities were proven to be epileptogenic by ECOG. In 4 patients, FMZ PET or AMT PET provided additional localizing information in identifying the epileptogenic zone. 7 patients underwent one-stage hemispherectomy. After extraoperative ECOG monitoring 2 patients underwent hemispherectomy, 1 subtotal hemispherectomy and the remaining 22 patients lobar/multilobar cortical resection. Thirteen had cortical dysplasia (4 with balloon cells), 6 had polymicrogyria, 3 had hemimegalencephaly, 3 had microdysgenesis, 2 had periventricular heterotopia, 2 had subcortical heterotopia, and one each had lissencephaly/subcortical band heterotopia spectrum, schizencephaly and unilateral perisylvian polymicrogyria. Two patients had associated corpus callosum dysgenesis. Mean follow-up period was 2.3 yrs. Twenty-five patients (78%) achieved Engel class I or II, whereas 6 had Engel class III or IV. However, these 6 surgical failures included 3 who had ‘palliative surgery’ (resection of the major focus with known bilateral epileptogenic foci), and 3 who had incomplete resection of the epileptogenic zone due to proximity to ‘eloquent’ cortex. One patient who underwent hemispherectomy died 2 days post-surgery due to DIC associated with sepsis. Conclusions: Conclusion: The outcome of epilepsy surgery in carefully selected patients with MCD can be favorable, even in MRI negative cases where PET is particularly helpful. Even in MRI-positive cases, PET scanning provides additional information in delineating the epileptogenic zone to improve surgical outcome.