Specific DTI seeding and diffusivity-analysis improve the quality and prognostic value of TMS-based deterministic DTI of the pyramidal tract

Abstract

ObjectNavigated transcranial magnetic stimulation (nTMS) combined with diffusion tensor imaging (DTI) is used preoperatively in patients with eloquent-located brain lesions and allows analyzing non-invasively the spatial relationship between the tumor and functional areas (e.g. the motor cortex and the corticospinal tract [CST]). In this study, we examined the diffusion parameters FA (fractional anisotropy) and ADC (apparent diffusion coefficient) within the CST in different locations and analyzed their interrater reliability and usefulness for predicting the patients' motor outcome with a precise approach of specific region of interest (ROI) seeding based on the color-coded FA-map.MethodsProspectively collected data of 30 patients undergoing bihemispheric nTMS mapping followed by nTMS-based DTI fiber tracking prior to surgery of motor eloquent high-grade gliomas were analyzed by 2 experienced and 1 unexperienced examiner. The following data were scrutinized for both hemispheres after tractography based on nTMS-motor positive cortical seeds and a 2nd region of interest in one layer of the caudal pons defined by the color-coded FA-map: the pre- and postoperative motor status (day of discharge und 3 months), the closest distance between the tracts and the tumor (TTD), the fractional anisotropy (FA) and the apparent diffusion coefficient (ADC). The latter as an average within the CST as well as specific values in different locations (peritumoral, mesencephal, pontine).ResultsLower average FA-values within the affected CST as well as higher average ADC-values are significantly associated with deteriorated postoperative motor function (p = 0.006 and p = 0.026 respectively). Segmental analysis within the CST revealed that the diffusion parameters are especially disturbed on a peritumoral level and that the degree of their impairment correlates with motor deficits (FA p = 0.065, ADC p = 0.007). No significant segmental variation was seen in the healthy hemisphere. The interrater reliability showed perfect agreement for almost all analyzed parameters.ConclusionsAdding diffusion weighted imaging derived information on the structural integrity of the nTMS-based tractography results improves the predictive power for postoperative motor outcome. Utilizing a second subcortical ROI which is specifically seeded based on the color-coded FA map increases the tracking quality of the CST independently of the examiner's experience. Further prospective studies are needed to validate the nTMS-based prediction of the patient's outcome.

Clinical Uses of Diffusion Tensor Imaging Fiber Tracking Merged Neuronavigation with Lesions Adjacent to Corticospinal Tract : A Retrospective Cohort Study

“…We concluded that a distance of 10 mm between tumor border and CST was sufficient to preserve motor function. Comparable results were also cited in some prior studies 33,35,37) . The tumor-CST distance may well be regarded as presumptive predictor of outcome, attributable in part to tumor edema.…”

Neurophysiology-Driven Parameter Selection in nTMS-Based DTI Tractography: A Multidimensional Mathematical Model

“…In order to improve the threshold selection, previous standardization attempts suggested a FL threshold of 110 mm and the implementation of a 100%-FAT criterium. The latter described the FA threshold at which only a thin fiber tract was visualized and all other FA values were described in relation to this 100%-FAT value as e.g., 75%-, 50%-or 25%-FAT (Frey et al, 2012;Weiss et al, 2015;Rosenstock et al, 2017;Weiss Lucas et al, 2017). The concept of performing fiber tracking with a FL threshold of 110 mm and a 75%-FAT resulted in a more objective tractography than the previous methods (Frey et al, 2012).…”

“…The modeled grid was imported into the BrainLab iPlan 3.0 software and fused to the original nTMS data, anatomical T1-weigthed MRI, and DTI dataset. In addition to the cortical ROIs, we created two subcortical ROIs for every subject: the first one (PON-ROI) was placed in the caudal pons based on the color-coded FA map (Rosenstock et al, 2017), while the second (PED-ROI) was located below the cerebellar peduncles to avoid aberrant tracts to the cerebellum. Furthermore, for later comparative analysis, we created an additional cortical ROI from the summation of nTMS points of positive MEPs (i.e., amplitude >50 µV), which were enlarged by 2 mm (nTMS-ROI) in line with the current clinical practice (Krieg et al, 2012).…”

Interobserver Agreement of White Matter Tract Involvement in Gliomas with Diffusion Tensor Tractography

“…DTT can identify eloquent tumors in subcortical motor pathways for presurgical planning. [18][19][20] One study reported that changes in diffusion parameters with glioma close to the corticospinal tract are the optimal factor in predicting injury to the corticospinal tract caused by a brain tumor. 18 Another study added that the diffusion parameters are particularly disturbed, and the degree of their impairment correlates with motor deficits.…”