gms | German Medical Science

Objective: Many patients with brain tumors adjacent to the primary motor (M1) region initially present with transient or permanent motor deficits. Factors like compression by tumor mass, infiltration, as well as the extent of the perifocal edema may contribute to the motor deficit. In order to assess the relevance of these factors, we analyzed the spatial relationship between M1 functions assessed with navigated transcranial magnetic stimulation (nTMS) and the anatomical and metabolic extension of tumors in the M1 region prior to surgery.

Method: To date, 21 patients with a brain tumor adjacent to the M1 region (glioblastoma (n=14), anaplastic astrocytoma (n=1), carcinoma metastasis (n=4), anaplastic ependymoma (n=1), lymphoma (n=1)) underwent an anatomical MRI protocol including a T2-weighted sequence, a gadolinium-contrast-enhanced sequence (GCE) and diffused tensor imaging as well as ¹⁸F-fluoroethyl-L-tyrosine (FET) PET for presurgical planning. Cortical M1 representations for the hand, foot and tongue were assessed by nTMS within 7 days. The corticospinal tract (CST) was tracked by setting the seeds to the nTMS hotspots and the brainstem, followed by volumetric analyses of the total and intersection volumes of the CST and the anatomically defined areas.

Results: 15 patients initially presented with hemiparesis or an isolated primary motor deficit, while 6 patients had not developed any deficit prior to admission. There was no statistical difference in the total perifocal edema volume between the motor deficit group (64.2 ±38.1 cm³, n=15) and the one without motor deficits (43.4 ± 28.6 cm³, n=6, p=.37). However, the relative volume of the functional fibers intersected by edema was greater in the primary motor deficit group (16.1 ± 13.1%) than in the patients without motor deficits (0.1 ± 0.0%, p<0.01). In contrast, the relative volume of cortical M1 representation intersected by the edematous area did not differ between the two groups (p=.24). There was also no difference in the GCE (p=.96) or the FET (p=.45) total tumor volume between those two groups.

Conclusions: The study implies that neither direct tumor infiltration of the M1 region or the CST nor the tumor volume nor the extension of perifocal edema in total may be the main causes for the primary motor deficit of brain tumor patients at initial presentation. In contrast, the extent of the perifocal edema affecting CST fibers seems to be responsible for motor deficits prior to surgery.