Clinicopathological associations in temporal lobe epilepsy patients utilising the current ILAE focal cortical dysplasia classification

Objectives: This study utilised the revised 2011 ILAE classification of focal cortical dysplasia (FCD) (Blümcke et al., 2011) to examine pathology in a cohort of children and adults who underwent temporal lobe epilepsy (TLE) surgery, and to describe the electroclinical and imaging features associated with these pathologies.

Methods: The sample population were children (n=26) and adults (n=47) who underwent TLE surgery between 2002 and 2011 at our institutions. Neuropathology and MRI studies were re-reviewed by experts blinded to the original diagnosis. EEG and clinical data including current seizure outcome were determined by patient file review and/or patient contact. Pre-operative data, post-operative outcome and pathological diagnoses were compared.

Results: The commonest pathology in the adult cohort was isolated hippocampal sclerosis (HS) (n=24, 51.1%) and in the paediatric cohort, isolated tumour (n=10, 38.5%). Overall, HS with associated FCD (FCD IIIA) was the third most common pathology (n=12, 16.4%). Temporal grey matter signal changes on MRI were associated with FCD IIIA (p=0.035). FCD IIIA had the poorest post-surgical seizure outcome compared to all other pathologies (p=0.026). A history of bilateral convulsive seizures was more common in adults (n=40, p<0.0005), and was associated with failure to achieve postoperative seizure freedom (p=0.045). Postoperatively, paediatric TLE had higher rates of seizure freedom (p=0.005) and more children had ceased medication (p<0.0005).

Significance: FCD IIIA is a comparatively common pathological subtype in TLE, with a poor post-surgical outcome. Pre-operative recognition of FCD IIIA may be feasible through grey matter signal change on MRI. Paediatric patients had a higher rate of seizure freedom than adults. Pre-operative bilateral convulsive seizures were associated with poor outcome after surgery.