Article
Preoperative mapping of cortical language areas by means of navigated repetitive transcranial magnetic stimulation: initial experience
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Authors
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Thomas Picht
- Neurochirurgie, Charité - Universitätsmedizin Berlin, Germany
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Olaf Suess
- Neurochirurgie, Charité - Universitätsmedizin Berlin, Germany
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Peter Vajkoczy
- Neurochirurgie, Charité - Universitätsmedizin Berlin, Germany
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Theodoros Kombos
- Neurochirurgie, Charité - Universitätsmedizin Berlin, Germany
| Published: | September 16, 2010 |
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Outline
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Objective: Intraoperative electrical stimulation of the exposed cortex is still the gold standard for reliable and accurate localization of cortical language representation. Repetitive transcranial magnetic stimulation (rTMS) is the only painless method which permits transient inhibition of cortical function by a series of stimuli. The aim of the present study was to evaluate the feasibility of navigated rTMS to perform non-invasive language mapping preoperatively.
Methods: Repetitive transcranial magnetic stimulation of the cortical language areas was performed in five healthy volunteers as well as in two patients with malignant gliomas of the fronto-opercular region and one patient with a metastasis of the dorsal middle temporal gyrus. After determining the resting motor threshold (RMT, a series of repetitive stimuli was applied at 110% RMT and at rates of 4, 8 and 10 Hz for 5 seconds over the presumed cortical language areas. Language tasks consisted of free speech, reading and counting or naming of objects which were presented 2 seconds after onset of stimulation. Spots where rTMS led to speech arrest, aphasic arrest or repeatable speech disturbance with normal contralateral responses were classified as speech areas.
Results: In three out of five volunteers and in the two patients with frontal gliomas a repeatable speech arrest could be elicited by stimulation of the dorsal inferior frontal gyrus and the basal aspect of the precentral gyrus. Stimulation of the dorsal superior and middle temporal gyrus led to a pro-longed response time in two out of five volunteers and in the patient with the temporal metastasis. Results were most robust at 110% RMT and 8 Hz frequency. Free speech and object naming had the highest sensitivity for detection of induced aphasic symptoms.
Conclusions: rTMS has the potential to identify areas inducing speech arrest on the dominant hemisphere in the fronto-opercular region. Stimulation of the dorsal temporal cortex yielded inconclusive results. Although the results are promising, the best stimulation parameters as well as the optimal language tasks still need to be defined. Furthermore a prospective comparison to the gold standard of intraoperative mapping is mandatory.
