Cortical Changes in Epilepsy Patients With Focal Cortical Dysplasia: New Insights With T₂ Mapping

In epilepsy patients with focal cortical dysplasia (FCD) as the epileptogenic focus, global cortical signal changes are generally not visible on conventional MRI. However, epileptic seizures or antiepileptic medication might affect normal-appearing cerebral cortex and lead to subtle damage.

To investigate cortical properties outside FCD regions with T₂ -relaxometry.

Prospective study.

Sixteen patients with epilepsy and FCD and 16 age-/sex-matched healthy controls.

3T, fast spin-echo T₂ -mapping, fluid-attenuated inversion recovery (FLAIR), and synthetic T₁ -weighted magnetization-prepared rapid acquisition of gradient-echoes (MP-RAGE) datasets derived from T₁ -maps.

Reconstruction of the white matter and cortical surfaces based on MP-RAGE structural images was performed to extract cortical T₂ values, excluding lesion areas. Three independent raters confirmed that morphological cortical/juxtacortical changes in the conventional FLAIR datasets outside the FCD areas were definitely absent for all patients. Averaged global cortical T₂ values were compared between groups. Furthermore, group comparisons of regional cortical T₂ values were performed using a surface-based approach. Tests for correlations with clinical parameters were carried out.

General linear model analysis, permutation simulations, paired and unpaired t-tests, and Pearson correlations.

Cortical T₂ values were increased outside FCD regions in patients (83.4 ± 2.1 msec, control group 81.4 ± 2.1 msec, P = 0.01). T₂ increases were widespread, affecting mainly frontal, but also parietal and temporal regions of both hemispheres. Significant correlations were not observed (P ≥ 0.55) between cortical T₂ values in the patient group and the number of seizures in the last 3 months or the number of anticonvulsive drugs in the medical history.

Widespread increases in cortical T₂ in FCD-associated epilepsy patients were found, suggesting that structural epilepsy in patients with FCD is not only a symptom of a focal cerebral lesion, but also leads to global cortical damage not visible on conventional MRI.

21 TECHNICAL EFFICACY STAGE: 3 J. MAGN. RESON. IMAGING 2020;52:1783-1789.