Abstracts

Rationale: Structural magnetic resonance imaging (MRI) is a cornerstone of epilepsy evaluation. Identifying a visible causative anomaly is one of the main predictors of surgical outcome. Despite this, many are diagnosed with MR negative focal epilepsy, even with high quality imaging interpreted by experts, prompting complex and invasive investigations. This is even more true in young children where incomplete myelination occults the findings of focal cortical dysplasia (FCD). Additional imaging markers of FCD may improve access to surgical management and prognosis. A particularly visible MRI phenotype was noted in an infant, like the one described in Epilepsia 2005; 46(12):1988-92 and was specifically sought in subsequent cases of epilepsy in infants.

Methods: Consecutive subjects evaluated for surgical management of drug-resistant infantile-onset epilepsy were identified. For those whose initial MRIs were initially reported as normal, early ( < 12 months) MRIs were reviewed by the treating epileptologist for the presence of locally advanced myelination. Investigations were otherwise completed according to usual local practices. Abnormalities were compared with subsequent imaging.

Results: Three additional cases of infantile-onset epilepsy were identified. The first subject’s initial MRI had readily identifiable abnormalities which were not initially reported. MRI at 26 months demonstrated subtle changes consistent with type II FCD. PET was unrevealing. Pathology revealed FCD IIa and the subject remains seizure free a year later. Subject 2 was diagnosed with FCD on MRI at 25 months, with early-life MRI reported normal. Review of this MRI revealed similar WM changes as subject 1. PET revealed congruent hypometabolism. Resection revealed FCD IIb, and the subject remains seizure free 9 months later. Subjects 3 and 4 were siblings with familial focal epilepsy. Bifrontal dysplasia was suspected in subject 3 initially. Review of the initial MRI revealed similar WM changes only in one frontal lobe, and 3T MRI confirmed unilateral involvement. Subject 4 had multiple previous MRIs, all reported normal. Review of the initial MRI revealed similar WM abnormalities, with findings of FCD II with transmantle sign confirmed on repeat MRI. Subject 3 and 4 had PET hypometabolism congruent with the suspected lesions. FCD IIa was demonstrated in both, and they remain seizure-free about 4 and 5 months later.

Conclusions: In epilepsy due to FCD II, MRI in the infantile period may reveal FCD as an area of locally advanced subcortical myelination, most visible on T2w sequences but usually not reported. This may be easily seen even on low quality imaging, especially in areas with little myelination such as the anterior frontal lobe. This may allow for earlier identification of FCD or, as suggested by Cross et al, to identify the presence or extent of FCD on later MRIs when the lesion may become harder to detect. Additionally, the identification of abnormal oligodendrocyte development in what is thought to be mostly a neuronal process may help advance the understanding of the epileptogenicity of FCD.

Funding: Please list any funding that was received in support of this abstract.: None.