Functional MRI interactions between dysplastic nodules and overlying cortex in periventricular nodular heterotopia

Abstract

Periventricular nodular heterotopia (PVNH) is a malformation of cortical development associated with epilepsy. It is unclear whether the epileptogenic focus is the nodule, overlying cortex, or both. We performed electroencephalography (EEG)–functional magnetic resonance imaging (fMRI) in a patient with bilateral PVNH, capturing 45 “left temporal” epileptiform discharges. The relative time at which fMRI-involved regions became active was assessed. Additionally, nodule–cortex interactions were explored using fMRI functional connectivity. There was EEG–fMRI activity in specific periventricular nodules and overlying cortex in the left temporoparietal region. In both nodules and cortex, the peak BOLD response to epileptiform events occurred earlier than expected from standard fMRI hemodynamic modeling. Functional connectivity showed nodule–cortex interactions to be strong in this region, even when the influence of fMRI activity fluctuations due to spiking was removed. Nonepileptogenic, contralateral nodules did not show connectivity with overlying cortex. EEG–fMRI and functional connectivity can help identify which of the multiple abnormal regions are epileptogenic in PVNH.