Periventricular nodular heterotopia: A challenge for epilepsy surgery

(A and B) T2-weighted (axial) and MPRAGE (sagittal) MR imaging show periventricular heterotopia in the right basal temporo-occipital area (marked by arrow). (C) FLAIR (axial) MR image shows no evidence for cortical malformations or cortical lesions. (D) T2-weigthed (coronar) image: the arrow points to a radial band reaching from the nodular heterotopia to the lateral cortex. (E and F) A typical MEG spike of the patient. Two distinct MSI foci are shown in a sagittal view (Nos. I and II).

(A) Streamtube visualization of the right optic radiation based on diffusion tensor imaging. (B) For navigation, a three-dimensional object representing the optic radiation (wrapping the individual fibers) and two distinct MSI foci (red) are generated. (C) Relation of optic radiation (visualized as streamlines) to MSI foci. (D–F) Sagittal/coronal/axial view of T1-weighted images with registered DTI and MSI data. Localization of focal epileptic activity is below the optic tract.

(A) Intraoperative electroencephalographic recordings with platinum-electrodes close to the two suspected spike foci as suggested by MSI (white arrows: temporobasal strip, thin white arrow: depth electrode to heterotopia). Additional measurements were picked up from the lateral cortical surface (hatched arrow). The electrode position was confirmed by intraoperative T1- and T2-weighted high-field-MR imaging. (B) MSI guided electrode implantation of intracerebral depth and subdural electrodes; spike activity in lateral cortex and periventricular heterotopia, the corresponding spike density distribution is shown (upper right). The neocortex shows predominant spike wave activity and 11–12s⁻¹ polyspikes during intraoperative ECoG. (C) Intraoperative MR-imaging after cortical resection of MSI-focus No. II (with platinum electrodes still in situ). MSI-focus No. I adjacent to the heterotopia was left intact.