gms | German Medical Science

Objective: Navigated transcranial magnetic stimulation (nTMS) in combination with tractography allows for non-invasive analysis of structural connectivity. The integrity of white matter can be assessed by fractional anisotropy (FA). It is already known that FA values vary in relation to different brain regions. Lower FA values in peritumoral locations correlate with an increased risk for postoperative motor deterioration. Along-tract statistical analysis enables detailed analysis of individual white matter integrity. Here, we examine its potential to detect corticospinal tract (CST) impairment in brain tumor patients, relating to increased surgical risk.

Methods: We measured and compared FA values bihemispherically in 20 patients with glioma grade III and IV. First, we used nTMS data to define cortical hand representation and used these spots as ROIs for tractography. Subsequently, we extracted 20 equally distributed cross-sections along each streamline of CST fiber bundles. Finally, we performed statistical analysis of the mean FA values of prior extracted cross-sections and investigated peritumoral pathology-induced white matter differences between the patients’ left and right hemisphere.

Results: Along-tract statistical analysis with 20 segmental CST cross-sections was successful in all patients. The tumorous hemispheres displayed significant differences in overall FA values compared to healthy hemispheres. Segmental analysis demonstrated significant differences of FA values between healthy and pathological hemispheres foremost in the peritumoral area (p=<0.047–p<=0.001), with lower segmental FA values on the level of the tumor.

Conclusion: Analysis of bihemispheric along-tract FA values allows for detailed detection of structural impairment of peritumoral CST. Consequently, along-tract analysis enables detailed assessment of white matter vulnerability before brain tumor surgery.