Abstracts

Rationale: Fluorine-18-fluorodeoxyglucose (FDG) positron emission tomography (PET) hypometabolism has been used primarily to localise the epileptogenic zone. Most studies of prognostic factors for outcome have not considered the relevance of hypometabolism remote from the focus. We investigated the surgical outcome of a large cohort of patients with neocortical epilepsy and their patterns of FDG-PET hypometabolism. Methods: We identified all patients who had undergone resective surgery for intractable neocortical epilepsy at Westmead and Royal Prince Alfred Hospitals, Sydney, Australia.between 1994 and 2004, had interictal FDG-PET study and were follow-up of at least two years after surgery. The topography of significant cortical and subcortical regions of glucose hypometabolism involving the epileptic focus and surrounding contiguous regions (perifocal hypometabolism) and those distant to and not contiguous with the perifocal hypometabolism (remote hypometabolism) was determined by SPM 2 (voxel threshold p=0.01, extent threshold≥125 voxels, uncorrected cluster-level significance p<0.05). This was compared with MRI, clinical and demographic variables using a multiple logistic regression model to identify independent predictors of seizure outcome. Results: Sixty-six neocortical epilepsy patients were studied (frontal lobe 23, neocortical temporal lobe 24, parietal lobe 6, occipital lobe 12). Of these, 63.3 % become seizure free postoperatively. On univariate analysis, the volume of perifocal hypometabolism did not differ significantly between seizure free patients or patients with persistent seizures. However, those with persistent seizures had a higher volume of remote hypometabolism (p<0.005). Multiple logistic regression analysis identified a larger volume of remote FDG-PET hypometabolism (p=0.002), older age at surgery (p=0.013) and absence of a localized MRI lesion (p=0.018) as independent predictors of seizure persistence after surgery. The presence of secondarily generalized tonic-clonic seizures (SGTCS) was associated with a larger volume of remote hypometabolism (p < 0.005). Conclusions: Remote glucose hypometabolism is associated with poor surgical outcome. The significant relationship between SGTCS and remote hypometabolism may reflect more extensive epileptogenicity.