Abstracts

Rationale: Drug-resistant focal epilepsy is often caused by focal cortical dysplasia (FCD). Across the cerebral cortex, the distribution of these lesions and the impact of a lesion’s location on clinical presentation and surgical outcome is largely unknown. We created a neuroimaging cohort of patients with individually mapped FCDs to determine factors associated with lesion location and predictors of postsurgical seizure freedom to aid presurgical decision-making.

Methods: The Multi-centre Epilepsy Lesion Detection (MELD) project collated a retrospective cohort of 580 patients with epilepsy due to FCD from 20 epilepsy centres worldwide. MRI-based maps of individual FCD lesions with accompanying demographic, clinical and surgical information were collected. We mapped the distribution of FCD lesions across the cerebral cortex. Logistic regression models were used to test for associations between lesion location and clinical data. Regression coefficients were tested for significance against those calculated on 1000 randomly permuted cohorts. A logistic regression model to predict seizure freedom, using 10-fold cross-validation, was fitted with duration of epilepsy, age of epilepsy onset, MRI-negative status, scanner, lesion overlap with eloquent cortex and lesion size. Sensitivity, specificity, positive predictive value and negative predictive value were calculated.

Results: FCDs were non-uniformly distributed across the brain, concentrating in the superior frontal sulcus, frontal pole and temporal pole (Figure 1A). Age of epilepsy onset, duration of epilepsy, age at MRI scan and lesion size were significantly related to lesion location (number of significant vertices > expected by chance p< 0·01) (Figure 2). Earlier epilepsy onset was associated with lesions in primary sensory areas while later epilepsy onset was associated with lesions in association cortices (Figure 2A). Lesions in temporal and occipital lobes tended to be larger than frontal lobe lesions (Figure 2D). Seizure freedom rates varied with FCD location, varying from around 30% in visual, motor and premotor areas to 75% in superior temporal and frontal gyri (Figure 1B). The predictive model of postsurgical seizure freedom had a positive predictive value of 70% and negative predictive value of 61%.