gms | German Medical Science

Objective: During the last decade evidence for brain plasticity after resection of low-grade gliomas in mainly speech relevant areas has been obtained. Thus, our aim was to evaluate motor cortex reorganization after tumor resection non-invasively by navigated transcranial magnetic stimulation (nTMS).

Method: Mapping of the motor cortex by nTMS was performed pre- and postoperatively in 14 patients (5 females, aged mean 35.4, range 15 - 52.3 years), separated by 21.4 ± 21.3 months. Moreover, 8 patients underwent a third nTMS mapping 27.6 ± 10.3 months after their second motor cortex evaluation, resulting in a follow-up period of 40.4 ± 20.2 months. Centers of gravity (CoGs) were calculated for every muscle representation area, and Euclidian distances (EDs) between CoGs over time were defined. Results were compared with data from 12 healthy patients, whose motor cortex had been examined by nTMS in two sessions at an interval of 10.3 ± 9.6 days.

Results: Histopathological examination revealed glioma grade I and IV each in one patient, grade II in five and grade III in 7 patients. In healthy subjects, CoGs of upper and lower limb muscle representation areas over both hemispheres differed 5.41 ± 2.76 mm over sessions. In patients, pre- and postoperatively pooled nTMS data did not differ significantly, whereas a reorganization of the leg motor cortex was observed during the further postoperative follow-up period (p=0.005 for the tibial anterior muscle; p=0.007 for the abductor hallucis muscle). In detail, a significant shift of their motor representation areas was identified in 2 patients between their second and third nTMS mapping.

Conclusions: nTMS allows for an individualized non-invasive and reliable evaluation of motor cortex reorganization after brain tumor removal and thus might encourage repeated tumor resection in case of residual tumor or tumor recurrence.