Computational brain anatomy in patients with temporal lobe epilepsy

BACKGROUND Temporal lobe epilepsy (TLE) is a frequent type of focal epilepsy that constitutes 30% to 50% of all epileptic syndromes. This medical condition is often associated with hippocampal sclerosis, however it can be due to cortical dysplasia, brain tumour, vascular malformation or without any evidence for pathology (cryptogenic). Even though the main symptoms are the seizures, epilepsy sometimes interferes with cognitive functions such as visual or verbal memory, language or attention. TLE is frequently pharmaco-­‐resistant and only a hippocampal resection helps patients to become seizure-­‐free. Temporal lobe epilepsy is also described as a progressive disorder that causes chronic brain tissue damages. History of febrile seizures and status epilepticus, frequency of seizures and age at onset of seizure, as well as epilepsy duration or years of anti-­‐epileptic drugs use are all factors that impact the gravity of the brain structure's damage. Magnetic resonance imaging (MRI) has undergone a considerable development and, nowadays, has become an essential clinical tool in the diagnosis of TLE. It is currently used to reveal precisely cerebral abnormalities that may induce seizures. PURPOSE The aim of this cross-­‐sectional study is to investigate the pattern of microstructural brain tissue characteristics (grey and white matter volumes) occurring in three clinically distinctive TLE entities: mesial temporal sclerosis (MTS), focal cortical dysplasia (FCD) and cryptogenic epilepsy. By comparing them to each other, we want to acquire in-­‐depth knowledge of their pathological mechanism. We use well-­‐established computational anatomy methodology -­‐ voxel-­‐ based morphometry (VBM) to investigate brain anatomy changes related to the present clinical phenotype. CONTRIBUTION OF THE STUDY In the past few years, there has been a lot of controversy concerning structural MRI findings in TLE. Most of the studies looked for informative brain changes in epilepsy with MTS compared with healthy controls. This study is the first to take into consideration all clinical aspects of TLE together -­‐ mesial temporal sclerosis, focal cortical dysplasia and cryptogenic epilepsy. MATERIAL AND METHODS In-­‐vivo anatomical brain imaging data (MRI at 1.5T) was acquired in patients with clinical diagnosis of temporal lobe epilepsy. TLE patients were divided in three groups according to radiological description of brain MRI findings -­‐ mesial temporal sclerosis [MTS_group], focal cortical dysplasia [Dysplasia_group] and cryptogenic epilepsy [NoMRI_group] and compared with healthy volunteers. VBM technique was used to identify brain tissues alterations (GM and WM). RESULTS We demonstrate that MTS showed similar grey and white matter volumes reduction in the hippocampus, thalamus and cerebellum ipsilateral to the epileptogenic focus when compared with cryptogenic epilepsy patients and healthy controls. The focal cortical dysplasia patients showed grey matter volume loss restricted to the thalamus