Particularities in differential diagnostics of epileptogenic brain malformations on the low-field MRI-device

Abstract

Background. It has been suggested that the part of the cryptogenic epilepsies is a consequence of minor-foci disorders of cortical architectonics, the diagnosis of which is not always possible due to the unavailability of MR-scanners with high magnetic induction.Objective: determination of the best options of the low-field MRI-device for visualization of epileptogenic brain malformations in children with symptomatic focal forms of epilepsy.Materials and methods. Were analyzed MRI data of 24 children undergoing investigations regarding for difficult-to-treat or pharmacoresistant forms of focal epilepsy in the Department of Magnetic-Resonance Tomography, Central Children Clinical Hospital of FMB Agency of Russia at 2015–2017. All the patients underwent brain MRI according to standard routine protocol. Simultaneously we review conclusions of epileptologist and the preliminary video-electroencefalographic monitoring data for determination of the optimal imaging protocol for every specific form of epilepsy. For imaging of the epileptogenic brain lesion the MRI study was conducted on open-ended device “Aperto” (Hitachi Ltd., Japan) of static magnetic field with the tension characteristics of 0.4 T. The thickness of the slices and the scan step was performed at 3.0 and 3.5 mm (the maximum value of slice thickness and step due to the technical conditions of the used scanner without losing in signalto-noise ratio) with the use of special positioning of slices in the coronal and axial projections, T2, T1, STIR, FLAIR weighted images perpendicular and parallel to the long axis of the hippocampus.Results and conclusion. In 24 patients were revealed structural brain changes that have neuroradiological signs of brain malformations. In all the patients this changes were associated with difficult to treat and drug-resistant forms of focal epilepsy. The newly identified malformations were observed in 10 patients, and in 3 cases the changes detected after previous MRI (including high-field MRI-devices) whose results were false-negative. In 11 patients diffuse brain abnormalities had been revealed, including the combinations of several hypogenesis and dysplastic pathologies. In 13 patients were marked different types of hemispheric and regional disorders of cortical development including focal cortical dysplasia. Extensive unilateral and bilateral changes were clearly distinguishable on the routine MRI. The low-tension technique approximated to the epileptic scanning protocol in some cases allowed to assess the affected area and revealed the combination of different variants of pathological cortical organization. In 7 cases the preliminary diagnosis based on the results of previous MRI studies including high-field MRI-devices. In 2 of these patients this changes were minor-focal, not visualized according to the routine MRI protocol, and had the differentiation characteristics between focal cortical dysplasia IIb/dysembryoplastic neuroepithelial tumor/ganglioglioma types. Disappointing results of visualization of mesial-basal temporal lobe regions aimed to detect small-caliber intracortical formations were observed. These patients contained a separate group of 12 children for whom extensive investigation which includes high-field MRI scan protocol on epileptic program was recommended.

Keywords

• drug-resistant focal epilepsy
• epileptogenic brain lesions
• magnetic resonance imaging
• low-field magnetic resonance scanner