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White matter bundle segmentation using diffusion MRI fiber tractography has become the method of choice to identify white matter fiber pathways in vivo in human brains. However, like other analyses of complex data, there is considerable variability in segmentation protocols and techniques. This can result in different reconstructions of the same intended white matter pathways, which directly affects tractography results, quantification, and interpretation. In this study, we aim to evaluate and quantify the variability that arises from different protocols for bundle segmentation. Through an open call to users of fiber tractography, including anatomists, clinicians, and algorithm developers, 42 independent teams were given processed sets of human wholebrain streamlines and asked to segment 14 white matter fascicles on six subjects. In total, we received 57 different bundle segmentation protocols, which enabled detailed volume-based and streamline-based analyses of agreement and disagreement among protocols for each fiber pathway. Results show that even when given the exact same sets of underlying streamlines, the variability across protocols for bundle segmentation is greater than all other sources of variability in the virtual dissection process, including variability within protocols and variability across subjects. In order to foster the use of tractography bundle dissection in routine clinical settings, and as a fundamental analytical tool, future endeavors must aim to resolve and reduce this heterogeneity. Although external validation is needed to verify the anatomical accuracy of bundle dissections, reducing heterogeneity is a step towards reproducible research and may be achieved through the use of standard nomenclature and definitions of white matter bundles and well-chosen constraints and decisions in the dissection process.

Background We introduce a user-friendly, standardized protocol for tractography of the major language fiber bundles. Method The introduced method uses dMRI images for tractography whereas the ROI definition is based on structural T1 MPRAGE MRI templates, without normalization to MNI space. ROIs for five language-relevant fiber bundles were visualized on an axial, coronal, or sagittal view of T1 MPRAGE images. The ROIs were defined based upon the tracts’ obligatory pathways, derived from literature and own experiences in peritumoral tractography. Results The resulting guideline was evaluated for each fiber bundle in ten healthy subjects and ten patients by one expert and three raters. Overall, 300 ROIs were evaluated and compared. The targeted language fiber bundles could be tracked in 88% of the ROI pairs, based on the raters’ result blinded ROI placements. The evaluation indicated that the precision of the ROIs did not relate to the varying experience of the raters. Conclusions Our guideline introduces a standardized language tractography method for routine preoperative workup and for research contexts. The ROI placement guideline based on easy-to-identify anatomical landmarks proved to be user-friendly and accurate, also in inexperienced test persons.

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Tumors infiltrating the motor system lead to significant disability, often caused by corticospinal tract injury. The delineation of the healthy-pathological white matter (WM) interface area, for which diffusion magnetic resonance imaging (dMRI) has shown promising potential, may improve treatment outcome. However, up to 90% of white matter (WM) voxels include multiple fiber populations, which cannot be correctly described with traditional metrics such as fractional anisotropy (FA) or apparent diffusion coefficient (ADC). Here, we used a novel fixel-based along-tract analysis consisting of constrained spherical deconvolution (CSD)-based probabilistic tractography and fixel-based apparent fiber density (FD), capable of identifying fiber orientation specific microstructural metrics. We addressed this novel methodology’s capability to detect corticospinal tract impairment. We measured and compared tractogram-related FD and traditional microstructural metrics bihemispherically in 65 patients with WHO grade III and IV gliomas infiltrating the motor system. The cortical tractogram seeds were based on motor maps derived by transcranial magnetic stimulation. We extracted 100 equally distributed cross-sections along each streamline of corticospinal tract (CST) for along-tract statistical analysis. Cross-sections were then analyzed to detect differences between healthy and pathological hemispheres. All metrics showed significant differences between healthy and pathologic hemispheres over the entire tract and between peritumoral segments. Peritumoral values were lower for FA and FD, but higher for ADC within the entire cohort. FD was more specific to tumor-induced changes in CST than ADC or FA, whereas ADC and FA showed higher sensitivity. The bihemispheric along-tract analysis provides an approach to detect subject-specific structural changes in healthy and pathological WM. In the current clinical dataset, the more complex FD metrics did not outperform FA and ADC in terms of describing corticospinal tract impairment.

OBJECTIVEMoyamoya vasculopathy (MMV) is a steno-occlusive cerebrovascular disease that can be treated by a surgical revascularization. All the revascularization techniques influence the blood supply of the scalp, with a risk for wound healing disorders. The authors’ aim was to analyze the wound healing process in the patients who underwent a direct or combined bypass surgery with a focus on different skin incisions.METHODSThe authors retrospectively identified all the patients with MMV who were treated surgically in their institution. Subsequently, they analyzed demographic data, clinical symptoms, surgical treatment, and detailed history of complications. Based on the evolution of their surgical techniques and the revascularization strategy to be used, the authors applied the following skin incisions: linear incision, curved incision, incomplete Y incision, and complete Y incision. Group comparisons regarding wound healing disorders were performed with significance testing using Fisher’s exact test.RESULTSThe authors identified 172 patients with MMV (61.6% moyamoya disease, 7% unilateral moyamoya disease, 29.7% moyamoya syndrome, and 1.7% unilateral moyamoya syndrome), of whom 124 underwent bilateral operations. One-quarter of the patients were juveniles. A total of 236 hemispheres were included in the analysis, of which 27.9% were treated by a combined procedure with encephalomyosynangiosis. Overall, 5.1% major and 1.7% minor wound complications occurred. The overall wound complication rate was lower in direct revascularization compared to combined revascularization (3% vs 15.2%). The lowest incidence of wound healing disorders was found in the linear incision group for the parietal superficial temporal artery branch (1.6%), followed by the incomplete Y incision group for the frontal branch of the superficial temporal artery (3.8%) in the direct bypass group. In the combined revascularization cohort, major or minor wound disorders appeared in 14.3% and 4.8%, respectively, in the complete Y incision group and in 4.2% (for both major and minor) in the curved incision group. The complete Y incision caused significantly more wound healing disorders compared to the remaining incision types (17.1% vs 3.1%, p = 0.007).CONCLUSIONSWound healing disorders are one of the major complications of revascularization surgery. Their incidence depends on the revascularization strategy and skin incision applied, with a complete Y incision giving the worst results.