2 research outputs found
Specific DTI seeding and diffusivity-analysis improve the quality and prognostic value of TMS-based deterministic DTI of the pyramidal tract
Object Navigated 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. Methods Prospectively 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).
Results Lower 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.
Conclusions Adding 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
A Novel Technique for Region and Linguistic Specific nTMS-based DTI Fiber Tracking of Language Pathways in Brain Tumor Patients
Navigated transcranial magnetic stimulation (nTMS) has recently been
introduced as a non-invasive tool for functional mapping of cortical language
areas prior to surgery. It correlates well with intraoperative
neurophysiological monitoring (IONM) findings, allowing defining the best
surgical strategy to preserve cortical language areas during surgery for
language-eloquent tumors. Nevertheless, nTMS allows only for cortical mapping
and postoperative language deficits are often caused by injury to subcortical
language pathways. Nowadays, the only way to preoperatively visualize language
subcortical white matter tracts consists in DTI fiber tracking (DTI-FT).
However, standard DTI-FT is based on anatomical landmarks that vary
interindividually and can be obscured by the presence of the tumor itself. It
has been demonstrated that combining nTMS with DTI-FT allows for a more
reliable visualization of the motor pathway in brain tumor patients.
Nevertheless, no description about such a combination has been reported for
the language network. The aim of the present study is to describe and assess
the feasibility and reliability of using cortical seeding areas defined by
error type-specific nTMS language mapping (nTMS-positive spots) to perform
DTI-FT in patients affected by language-eloquent brain tumors. We describe a
novel technique for a nTMS-based DTI-FT to visualize the complex cortico-
subcortical connections of the language network. We analyzed quantitative
findings, such as fractional anisotropy values and ratios, and the number of
visualized connections of nTMS-positive spots with subcortical pathways, and
we compared them with results obtained by using the standard DTI-FT technique.
We also analyzed the functional concordance between connected cortical nTMS-
positive spots and subcortical pathways, and the likelihood of connection for
nTMS-positive vs. nTMS-negative cortical spots. We demonstrated, that the
nTMS-based approach, especially what we call the “single-spot” strategy, is
able to provide a reliable and more detailed reconstruction of the complex
cortico-subcortical language network as compared to the standard DTI-FT. We
believe this technique represents a beneficial new strategy for customized
preoperative planning in patients affected by tumors in presumed language
eloquent location, providing anatomo-functional information to plan language-
preserving surgery