Fiber-tracking does not accurately estimate size of fiber bundle in pathological condition: initial neurosurgical experience using neuronavigation and subcortical white matter stimulation.

The fiber-tracking method enables in vivo visualization of the white matter tracts of the brain using a diffusion tensor MR imaging technique. While this method represents a promising tool in the field of neurosurgery, especially when confronted with brain tumors in eloquent areas, its reliability remains unknown. We present here our preliminary validation of tractography in human subjects harboring brain tumors by comparing the results produced by neuronavigation and electrical white matter stimulation in two patients with gliomas in the eloquent area. Although we were able to visualize the pyramidal tract with the fiber-tracking technique, the images failed to present the actual size of the fiber bundles. Here we discuss the advantages and limitations of fiber-tracking in the field of neurosurgery.

Volumetric thermal devascularization of large meningiomas.

OBJECT: Controlling hemorrhage is crucial in the safe and efficient removal of large meningiomas. Intravascular embolization is not always a satisfactory means of accomplishing this goal because of the procedure's hemostatic effect and risk of complications. The authors in this study used a volumetric thermal ablation technique incorporating radiofrequency energy, image guidance, and local temperature control to devascularize tumor tissue. METHODS: Five patients with large meningiomas were treated. The target and orientation of the radiofrequency thermal ablation (RFTA) were simulated preoperatively to maximize devascularization of the lesion without thermal injury to adjacent critical structures. Image fusion, three-dimensional reconstruction, and image-guided methods provided for optimized trajectories and targets for insertion of the RFTA needle. During ablation, local temperatures of the tissue being cauterized were monitored continuously to limit the ablated lesion to within the target volume. The effects of devascularization and the softening of the tumor parenchyma facilitated lesion removal. The intracranial ablated meningioma changed into necrotic tissue and shrank within a few months. Histopathological examination of the ablated lesion revealed sharply demarcated coagulation necrosis. CONCLUSIONS: Volumetric thermal devascularization can be applied safely in the treatment of large meningiomas to facilitate surgical manipulation of the lesion as well as to reduce its size palliatively. The procedure's usefulness should be studied further in a larger number of cases with different tumor characteristics.

Determination of language dominance with synthetic aperture magnetometry: comparison with the Wada test.

Cerebral dominance for language function was investigated with synthetic aperture magnetometry (SAM). The results were compared with those of the Wada test. SAM is a spatial filtering technique that enables demonstration of the spatiotemporal distribution of oscillatory changes (synchronization and desynchronization) in magnetoencephalography (MEG) signals elicited by specific brain activation. MEG was conducted during a silent reading task in 20 consecutive preoperative neurosurgical patients who also underwent a Wada test. The spatial distribution of oscillatory changes related to silent reading was shown tomographically with SAM as statistical images. Language dominance was estimated by the laterality index, which scales the lateralization of the beta (13-25 Hz) and low gamma (25-50 Hz) band desynchronizations in the inferior frontal gyrus (IFG) or middle frontal gyrus (MFG). Oscillatory changes were distributed multifocally and bilaterally in the occipital cortex, IFG or MFG, and temporo-parieto-occipital border regions. In 19 patients (95%), language lateralization estimated by the laterality index was congruent with the result of the Wada test. In left-handed patients, SAM analysis clearly differentiated language dominance (left, right, or bilateral), and the findings were confirmed by the Wada test. Lateralization of beta or low gamma band desynchronizations in the IFG or MFG is a good indicator of the side of language dominance. Reliability of MEG imaging with SAM is sufficient to evaluate language dominance preoperatively in neurosurgical patients.