Black Line Sign in Focal Cortical Dysplasia IIB: A 7T MRI and Electro-clinico-pathologic Study.

We aim to provide detailed imaging-electro-clinico-pathological characterization of the black line sign, a novel MRI marker for focal cortical dysplasia (FCD) IIB.7T T2*-weighted-gradient-echo (T2*w-GRE) images were retrospectively reviewed in a consecutive cohort of medically intractable epilepsy patients with pathology-proven FCD II, for the occurrence of the black line sign. We examined the overlap between the black line region and the seizure onset zone (SOZ) defined by intracranial EEG (ICEEG), and additionally assessed whether complete inclusion of the black line region in the surgical resection associated with postoperative seizure freedom. Histopathological specimen was aligned with the MRI to investigate the pathological underpinning of the black line sign. Region-of-interest-based qMRI analysis on 7T T1 map was performed in the black line region, the entire lesional gray matter (GM), as well as contralateral/ipsilateral normal gray and white matter (WM).We included 20 patients with FCD II (14 IIB and 6 IIA). The black line sign was identified in 12/14 (85.7%) of FCD IIB and 0/6 of FCD IIA on 7T T2*w-GRE. The black line region was highly concordant with the ICEEG-defined SOZ (5/7 complete and 2/7 partial overlap). Seizure freedom was seen in 8/8 patients whose black line region was completely included in the surgical resection; in the two patients whose resection did not completely include the black line region, both had recurring seizures. Inclusion of the black line region in the surgical resection was significantly associated with seizure-freedom (p=0.02). QMRI analyses showed T1 mean value of the black line region was significantly different from WM (p<0.001), but similar to GM. Well-matched histopathological slices in one case revealed accumulated dysmorphic neurons and balloon cells in the black line region.The black line sign may serve as a noninvasive marker for FCD IIB. MRI-pathology and qMRI analyses both suggest the black line region was an abnormal GM component within the FCD. Being highly concordant with ICEEG-defined SOZ, and significantly associated with seizure-freedom when included in resection, the black line sign may contribute to the planning of ICEEG/surgery of medically intractable epilepsy patients with FCD IIB.Classification of Evidence: This study provides Class II evidence that in individuals with intractable focal epilepsy undergoing resection who have a 7T MRI with adequate image quality, the presence of the black line sign may suggest FCD IIB, be concordant with SOZ from ICEEG, and be associated with more seizure freedom if fully included in resection.