Date Published: March 7, 2019
Publisher: Public Library of Science
Author(s): Max Zimmermann, Karl Rössler, Martin Kaltenhäuser, Peter Grummich, Nadja Brandner, Michael Buchfelder, Arnd Dörfler, Konrad Kölble, Andreas Stadlbauer, Christos Papadelis.
Preoperative functional mapping in the vicinity of brain lesion is of high importance for avoiding complications in surgical management. However, space-occupying lesions may lead to functional reorganization or decreased BOLD activity.
Therefore in 13 patients with cerebral gliomas or brain arterio-venous malformations/ hemangioma fMRI- and MEG-based cortical localizations of motor and somatosensory cortical activation pattern were compared in order to investigate their congruency.
Localization of cortical sensorimotor areas with fMRI and MEG showed good congruency with a mean spatial distance of around 10 mm, with differences depending on the localization method. The smallest mean differences for the centroids were found for MEF with MNE 8 mm and SEF with sLORETA 8 mm. Primary motor area (M1) reorganization was found in 5 of 12 patients in fMRI and confirmed with MEG data. In these 5 patients with M1-reorganization the distance between the border of the fMRI-based cortical M1-localization and the tumor border on T1w MR images varied between 0–4 mm, which was significant (P = 0.025) different to the distance in glioma patients without M1-reorganization (5–26 mm).
Our multimodal preoperative mapping approach combining fMRI and MEG reveals a high degree of spatial congruence and provided high evidence for the presence of motor cortex reorganization.
Neurosurgical procedures of lesions adjacent to eloquent brain areas are associated with a risk of postoperative dysfunction and always represent a challenge in neurosurgical decision making. Given the direct correlation between extent of tumor resection and clinical outcome, an exact mapping of sensorimotor (SM) areas in patients with perirolandic lesions can avoid irreversible impairment of SM function and facilitate a more radical resection, thus increasing both postoperative quality of life and survival time . Therefore, preoperative characterization of the functional anatomy in the vicinity of the lesion is of high importance for effective surgical management. However, it is often difficult to depict the relation of the lesion to functional important structures , especially when edema or mass lesions are present that distort the local anatomy of the brain. Furthermore, space-occupying lesions may lead to functional reorganization and alter the topographic organization of the cortex [3,4]. Previous studies provided examples for lesion-induced brain plasticity leading to considerable regional shifts of functional brain areas [5–11]. However, lesion-induced transhemispheric cortical reorganization to homologous brain regions (homotopic reorganization) in adult patients is considered controversial in the scientific community .
From the 13 patients included in this study (Table 1), one patient (ID 1) did not tolerate fMRI and another (ID 13) declined MEG examination. In two patients (IDs 10, 11) with dental implants the quality of the MEG data was insufficient because of magnetic artefacts. Overall fMRI data, MEG recordings and MEG and fMRI data of SM function prior to lesion resection were analyzed for twelve, ten and nine patients, respectively.
Functional MRI is used regularly to depict brain function near gliomas for preoperative surgical planning. But it’s a matter of discussion, whether BOLD areas actually represent neuronal activity, whether disappearance of a BOLD signal is equal to non-existent neuronal activity and whether reorganization of a M1 area actually exists. To investigate these unresolved scientific questions, we used a combination of fMRI and MEG for the characterization of cortical SM functions in the vicinity of cerebral gliomas and brain AVM/Hs.
The comparison of localization results of fMRI and MEG reveals a high degree of spatial congruence in healthy volunteers and preoperative patients with cerebral lesions. This multimodal approach of functional mapping demonstrates the occurrence of M1 reorganization in close proximity to high-grade gliomas, excluding neurovascular uncoupling by MEG confirmation. The superior temporal resolution of MEG allowed detecting an activational delay between the contralateral and the ipsilateral M1 areas which may contribute to a better understanding of the reorganization process.