Description

Focal epilepsies are a very heterogeneous group comprising epilepsies of structural, genetic, metabolic, immune and infectious etiologies. In daily practice, epilepsy is considered as structural if lesions are visible on brain MRI in a location consistent with electro-clinical data. In the absence of visible lesion and clinico-biological arguments for a genetic, metabolic, immune or infectious cause, these epilepsies can be divided into two groups: self-limited focal epilepsies (formerly called idiopathic or functional), such as benign epilepsy with centrotemporal spikes (SLECTS) and secondly epilepsies of unknown causes. This classification underlines the idea that a lesion might be responsible for the epileptic disease but could be invisible due to the lack of sensitivity of our current diagnostic methods, especially in imaging.

The prevalence of patients with non lesional epilepsy defined by MRI is significantly higher in children (31%) than in adults (21%). Epileptic patients with normal conventional MRI have a lower chance of having surgery than those with lesions demonstrated by presurgical MRI and, if so, less chance of becoming seizure-free. It can be challenging to depict brain volume abnormalities in the pediatric population on MRI. The major challenge is therefore to raise sensitivity of brain imaging analysis. Voxel-based morphometric MRI post-processing in MRI-negative epilepsies can be a practical and valuable tool to aid subtle MRI abnormalities detection and confirm visually identified questionable abnormalities in patients with focal epilepsy.

In this study, we prospectively included children with suspected focal epilepsy having a brain MRI using a MP2RAGE sequence and a post-processing morphometric analysis program (MAP) allowing us to obtain automatically both brain volumetry and T1 relaxometry. The MAP has been validated with reference ranges in healthy children. Our hypothesis was that the quantitative information will improve the sensitivity of brain MRI in children with suspected focal epilepsy. The objectives were to compare the rate of detection of a focal cerebral lesion on the brain MRI carried out during the exploration of suspected focal epilepsy without then with the quantitative volumetry and T1 relaxometry obtained in the inclusion center and then by double anonymized review.