Introduction:
This study investigates whether the middle frontal gyrus (MFG) can be used as an indicator for language hemispheric dominance in brain tumor patients using task-free resting state fMRI (rsfMRI). We hypothesize no significant difference in language lateralization between the MFG and Broca’s Area (BA) and that the MFG can serve as a simple and reliable means of measuring language laterality.
Methods:
51 patients with glial neoplasms. Using rsfMRI, the MFG was compared to BA for voxel activation, language laterality index (LI) and the effect of tumor grade on LI. LI derived by rsfMRI and task-based fMRI was compared in a subset of 40 patients.
Results:
Voxel activations in the left MFG and left BA were positively correlated (r = 0.47, p<0.001). Positive correlations were seen between the LI of BA and LI of MFG regions (r = 0.56, p < 0.0005). 27/40 patients (67.5%) showed concordance of LI based on BA using rsfMRI with LI based on a language task. 30/40 patients (75%) showed concordance of LI based on the MFG using rsfMRI with LI based on a language task.
Conclusion:
MFG is comparable to BA in its ability to determine hemispheric dominance for language using rsfMRI. Our results suggest the addition of rsfMRI of MFG to the list of noninvasive modalities that could be used in glioma patients to evaluate hemispheric dominance of language prior to tumor resection. In patients who cannot participate in traditional task-based fMRI, rsfMRI offers a task-free alternate to presurgically map eloquent cortex.
Purpose
The purpose of this study was to compare the deterministic and probabilistic tracking methods of diffusion tensor white matter fiber tractography in patients with brain tumors.
Materials and Methods
We identified 29 patients with left brain tumors <2 cm from the arcuate fasciculus who underwent pre-operative language fMRI and DTI. The arcuate fasciculus was reconstructed using a deterministic Fiber Assignment by Continuous Tracking (FACT) algorithm and a probabilistic method based on an extended Monte Carlo Random Walk algorithm. Tracking was controlled using two ROIs corresponding to Broca’s and Wernicke’s areas. Tracts in tumoraffected hemispheres were examined for extension between Broca’s and Wernicke’s areas, anterior-posterior length and volume, and compared with the normal contralateral tracts.
Results
Probabilistic tracts displayed more complete anterior extension to Broca’s area than did FACT tracts on the tumor-affected and normal sides (p < 0.0001). The median length ratio for tumor: normal sides was greater for probabilistic tracts than FACT tracts (p < 0.0001). The median tract volume ratio for tumor: normal sides was also greater for probabilistic tracts than FACT tracts (p = 0.01).
Conclusion
Probabilistic tractography reconstructs the arcuate fasciculus more completely and performs better through areas of tumor and/or edema. The FACT algorithm tends to underestimate the anterior-most fibers of the arcuate fasciculus, which are crossed by primary motor fibers.
BACKGROUND AND PURPOSE
The corticobulbar tract of the face and tongue, a critical white matter tract connecting the primary motor cortex and the pons, is rarely detected by deterministic DTI fiber tractography. Detection becomes even more difficult in the presence of a tumor. The purpose of this study was to compare identification of the corticobulbar tract by using deterministic and probabilistic tractography in patients with brain tumor.
MATERIALS AND METHODS
Fifty patients with brain tumor who underwent DTI were studied. Deterministic tractography was performed by using the fiber assignment by continuous tractography algorithm. Probabilistic tractography was performed by using a Monte Carlo simulation method. ROIs were drawn of the face and tongue motor homunculi and the pons in both hemispheres.
RESULTS
In all subjects, fiber assignment by continuous tractography was ineffectual in visualizing the entire course of the corticobulbar tract between the face and tongue motor cortices and the pons on either side. However, probabilistic tractography successfully visualized the corticobulbar tract from the face and tongue motor cortices in all patients on both sides. No significant difference (P < .08) was found between both sides in terms of the number of voxels or degree of connectivity. The fractional anisotropy of both the face and tongue was significantly lower on the tumor side (P < .03). When stratified by tumor type, primary-versus-metastatic tumors, no differences were observed between tracts in terms of the fractional anisotropy and connectivity values (P > .5).
CONCLUSIONS
Probabilistic tractography successfully reconstructs the face- and tongue-associated corticobulbar tracts from the lateral primary motor cortex to the pons in both hemispheres.
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