Implications of Extracranial Distortion in Ultra-High-Field Magnetic Resonance Imaging for Image-Guided Cranial Neurosurgery.

BACKGROUND: Ultra-high-field magnetic resonance imaging (MRI) of the brain is attractive for image guidance during neurosurgery because of its high tissue contrast and detailed vessel visualization. However, high-field MRI is prone to distortion artifacts, which may compromise image guidance. Here we investigate intra- and extracranial distortions in 7-T MRI scans. METHODS: Five patients with and 5 patients without skin-adhesive fiducials received magnetization-prepared T1-weighted 7-T MRI and standard 3-T MRI scans. The 7- and 3-T images were rigidly coregistered and compared. Intracranial distortions were evaluated qualitatively, whereas shifts at the skin surface and shifts of the center positions of skin-adhesive fiducials were measured quantitatively. Moreover, we present an illustrative case of an ultra-high-field image-guided skull base meningioma resection. RESULTS: We found excellent intracranial correspondence between 3- and 7-T MRI scans. However, the average maximum skin shift was 6.8 ± 2.0 mm in group A and 5.2 ± 0.9 mm in group B. The average maximum difference between the skin-adhesive fiducial positions was 5.6 ± 3.1 mm in group B. In our tumor resection case, the meningioma blood supply could be targeted early thanks to 7-T image guidance, which made subsequent tumor removal straightforward. CONCLUSIONS: There are no visible intracranial distortions in magnetization-prepared T1-weighted 7-T MRI cranial images. However, we found considerable extracranial shifts. These shifts render 7-T images unreliable for patient-to-image registration. We recommend performing patient-to-image registration on a routine (computed tomography scan or 3-T magnetic resonance) image and subsequently fusing the 7-T magnetic resonance image with the routine image on the image guidance machine, until this issue is resolved.

Simulating Internal Carotid Artery Injury during Transsphenoidal Transclival Endoscopic Surgery in a Perfused Cadaver Model.

Introduction Managing internal carotid artery (ICA) injury during extended endoscopic transsphenoidal surgery is an extreme challenge. We aimed to find a possible surgical treatment strategy. Methods We operated seven fresh, perfused cadaver heads with a transsphenoidal endoscopic approach of the ICA using a three-dimensional-high definition (3D-HD) endoscope. We made a paraclival ICA leak, which we tried to manage with clips and microsutures. Results Accurate transsphenoidal clip application on the ICA was impossible with standard aneurysm clips and applier. It was only feasible with a 9 mm slightly bended clip that could be opened from the inside and be applied with a dedicated flexible thin applier. Transsphenoidal suturing of an ICA leak was impossible from the ipsilateral nostril or with standard microinstruments. Suturing was only feasible from the contralateral nostril using flexible microinstruments with a thin 90-mm shaft. This was technically very challenging and involved a steep learning curve. Conclusion Tamponade with muscle or fat and a quick transfer to the angiography suite for endovascular control remains the preferable option in case of an ICA leak during endoscopic transsphenoidal surgery. If tamponade gives insufficient initial control, ICA clipping could be possible with dedicated instruments, with risk of increasing the defect, stenosis, or occlusion of the vessel. Transsphenoidal ICA suturing remains extremely difficult, and laboratory practice seems essential.

Functional and structural brain networks in epilepsy: what have we learned?

Brain functioning is increasingly seen as a complex interplay of dynamic neural systems that rely on the integrity of structural and functional networks. Recent studies that have investigated functional and structural networks in epilepsy have revealed specific disruptions in connectivity and network topology and, consequently, have led to a shift from "focus" to "networks" in modern epilepsy research. Disruptions in these networks may be associated with cognitive and behavioral impairments often seen in patients with chronic epilepsy. In this review, we aim to provide an overview that would introduce the clinical neurologist and epileptologist to this new theoretical paradigm. We focus on the application of a theory, called "network analysis," to characterize resting-state functional and structural networks and discuss current and future clinical applications of network analysis in patients with epilepsy.