Discrimination of epileptogenic lesions and perilesional white matter using diffusion tensor magnetic resonance imaging

Abstract

The aim of this study was to evaluate whether ganglioglioma (GGL), dysembryoplastic neuroepithelial tumour (DNET) and FCD (focal cortical dysplasia) are distinguishable through diffusion tensor imaging. Additionally, it was investigated whether the diffusion measures differed in the perilesional (pNAWM) and in the contralateral normal appearing white matter (cNAWM). Six GGLs, eight DNETs and seven FCDs were included in this study. Quantitative diffusion measures, that is, axial, radial and mean diffusivity and fractional anisotropy, were determined in the lesion identified on isotropic T2 or FLAIR-weighted images and in pNAWM and cNAWM, respectively. DNET differed from FCD in mean diffusivity, and GGL from FCD in radial diffusivity. Both types of glioneuronal tumours were different from pNAWM in fractional anisotropy and radial diffusivity. For identifying the tumour edges, threshold values for tumour-free tissue were investigated with receiver operating characteristic analyses: tumour could be separated from pNAWM at a threshold ≤ 0.32 (fractional anisotropy) or ≥ 0.56 (radial diffusivity) *10^-3 mm²/s (area under the curve 0.995 and 0.990 respectively). While diffusion parameters of FCDs differed from cNAWM (radial diffusivity (*10^-3 mm/s²): 0.74 ± 0.19 vs. 0.43 ± 0.05; corrected p-value < 0.001), the pNAWM could not be differentiated from the FCD.

Keywords: Epilepsy associated lesions; MRI; diffusion tensor imaging; focal cortical dysplasia; long-term epilepsy-associated tumours.

Figure 1.

Panel of representative images. In (a) to (c) examples for focal cortical dysplasias type IIA ((a) and (b)) and IB (c) are given. In (d) to (f) gangliogliomas WHO °I, and in (g) to (I) dysembryoplastic neuroepithelial tumours are displayed. Arrows indicate all pathologies.

Figure 2.

Receiver operating characteristic (ROC) analysis of radial diffusivity (red) and fractional anisotropy (blue) for the differentiation between tumour and perilesional normal appearing white matter. The ROC analysis of the fractional anisotropy revealed an area under the curve (AUC) of 0.995 (corrected p-value (p_corr) < 0.001): With a fractional anisotropy of 0.32 it is possible to identify all tumours (dysembryoplastic neuroepithelial tumours (DNETs) and gangliogliomas (GGLs)) with a sensitivity of 100% and a specificity of 93% (confidence interval (CI): 0.785–1.0). The ROC analysis of the radial diffusivity revealed an AUC of 0.990 (p_corr < 0.001): With a radial diffusivity of 0.56, all tumours (DNETs and GGLs) can be reliably identified with a sensitivity of 100% and a specificity of 93% (CI: 0.785–1.0).