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