Imaging of malformations of cortical development

Abstract

Malformations of cortical development (MCD) include a broad range of disorders that result from disruption of the major steps of cortical development: cell proliferation in germinal zones, neuronal migration and cortical organization. With the improvement and increased utilization of modern imaging techniques, MCD have been increasingly recognized as a major cause of seizure disorders. The advent of Magnetic Resonance Imaging (MRI), in particular, has revolutionized the investigation and the treatment of patients with epilepsy. High-resolution MRI may elucidate the type, the extension and the localization of MCD; therefore, in a group of patients suffering from drugresistant partial epilepsy (DRPE), MRI greatly contributes to the identification of subjects who are suitable for surgical treatment. In the recent past, many efforts were addressed to establish the MRI diagnostic criteria for a peculiar group of MCD, namely focal cortical dysplasias (FCD), histopathologically distinguished as types I and II. Some subtle FCD, which were previously cryptic to imaging investigation, can now be recognized by MRI, however their detection and specification remains challenging. This review will re-visit the neuroimaging findings, including structural MRI, PET, co-registered PET/MRI, MEG and diffusion tensor imaging (DTI) of FCD types I and II. Three major issues will be discussed: 1) the morphological MRI features of the FCDs, 2) the utility of PET and MEG and the use of co-registration methods and 3) diffusion tensor imaging (DTI) as a future modality of investigation, which may add additional informations regarding the microstructure of the grey matter (GM) and white matter (WM) in cortical dysplasia.

Focal cortical dysplasia type IIa and IIb: MRI aspects in 118 cases proven by histopathology

“…All of these limitations emphasise the need for a careful redefinition of the terminology used in imaging descriptions of FCD [17]; in cases with a blurred GM/WM junction and apparently thickened cortex on conventional MRI, our suggestion is to report "pseudo-thickening", unlike in cases with a sharply defined GM/WM junction and seemingly normal cortical thickness. In addition, we observed differences in the distribution of some MRI signs (cortical thickening, GM/WM blurring and WM signal alterations) inside the larger lesions, because they sometimes involved the entire lesion and sometimes had a focal distribution.…”

“…Inside wider lesions, we also analysed the distribution of these variables and WM signal changes and classified them as focal or diffused. All of the MRI variables were selected on the basis of our radiological experience and previous published FCD II data [1,[8][9][10][11][12][13][14][15][16][17].…”

“…Many published studies have described the MRI characteristics of FCD II [1,[8][9][10][11][12][13][14][15][16][17], but none has yet systematically evaluated the presence of each individual MRI sign in a large series of patients with histologically verified FCD II in an attempt to identify differential imaging features for the two FCD II subgroups (IIa and IIb). We retrospectively reviewed the MRI characteristics of a large cohort of patients undergoing surgery for DRPE and histologically characterised having FCD IIa or FCD IIb.…”

Epileptogenic networks of type II focal cortical dysplasia: A stereo-EEG study

“…The presence of dysplasia was established by means of MRI in accordance with the current radiological criteria for a diagnosis of type II FCD (Blümcke et al, 2011;Colombo et al, 2009). The patients' mean age at seizure onset was 9.8 ± 3.9 years, and the mean duration of epilepsy was 15.1 ± 10.4 years.…”

FDG-PET improves surgical outcome in negative MRI Taylor-type focal cortical dysplasias

“…Despite intensive expertise, best-practice MRI sequences, and new high-field MRI (3 Tesla), all centers report missed TTFCD cases. 10,33 18 FDG-PET is reported to have a high sensitivity to detect TTFCDs with areas of hypometabolism in 60% to 92%. 32,[34][35][36] However, in these series, MRI scans were in most instances positive, so the contribution of PET was not emphasized at this time.…”