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nTMS, DCS and fMRI: perioperative assessment in central
region tumours
Andrea Szelényi, MD PhD1, Marie-Terese Forster, MD1, Elke Hattingen, MD PhD2
1Department for Neurosurgery, 2Department for Neuroradiology, Hospital of the Johann Wolfgang Goethe University, Frankfurt am Main, Germany Introduction
In cerebral tumour surgery, the recent change of treatment paradigm includes a more aggressive
surgical approach, as there is increasing evidence that the amount of tumour resection correlates
with the recurrent free survival time. Despite the desire of the largest resection possible, the
postoperative well-being and unchanged neurological status of the patient is precept. To achieve
such an aim in tumours adjacent to the motor cortex, precise preoperative planning and intra-
operative assessment of the motor area is essential.
Thus we compared the preoperative motor cortex mapping results of fMRI and navigated transcranial magnetic stimulation (nTMS) with the maps created by independently performed direct electrocortical stimulation (DCS). Methods
fMRI
The MRI studies were performed on a 3 Tesla Magnetom Al egra Scanner (Siemens Medical
Solutions, Erlangen, Germany). Structural 3-dimensional isovolumetric T1-weighted data were
acquired using a magnetization-prepared rapid-acquisition gradient echo (MPRAGE) sequence.
Functional MRI was performed in a block design experiment using a blood oxygenation level-
dependent (BOLD)-sensitive echo planar imaging (EPI) sequence. The patients performed a simple
visual y guided motor task. Mapping data was only col ected for patients able to perform the tasks.
nTMS nTMS was performed with the NBS System (Nexstim Oy, Finland). After determining the hot spot for the ID1 muscle by a figure-of-8 coil, the motor threshold (MT) was set according to the Awiszus protocol. Mapping was further performed at 110% of MT. Individual 3D anatomical MRI data sets with superimposed fMRI data were integrated in the NBS workstation. Each spot was stimulated twice; the data was analyzed post-hoc and used to create a response map for each individual muscle. MEPs were recorded from the ID1 muscle, additional muscles were chosen according to the tumour location and included the biceps brachii, extensor digitorum communis, thenar, anterior tibial, abductor hal ucis and orbicularis oris muscles. DCS Intra-operatively, motor cortex mapping was performed with DCS using a monopolar anodal probe (2mm diameter). Stimulation parameters consisted of a train of five pulses with an individual pulse width of 500 ms and an inter-stimulus interval of 2 ms. The maximum intensity was limited to 25 mA. During surgery, the coordinates of each DCS site were unambiguously defined and integrated Published in: Abstracts from the 1st. International Workshop on Navigated Brain Stimulation in Neurosurgery, 5-6; March 1, 2010

into the neuronavigation system. A post-hoc comparison of the coordinates of nTMS, fMRI and DCS was performed. Data analysis
Intra-operatively, the preoperative mapping results were not displayed on the neuronavigation
system. The surgeon was therefore blinded towards the nTMS results while performing DCS. fMRI
mapping data were first imported into the NBS System. To compare DCS with NBS and fMRI, all data
were entered post-operatively into a Stealth Station® Neuronavigation System (Medtronic,
Minneapolis, MN, USA) for analysis.
Results
Preliminary results from 11 patients (fMRI data were obtained in 10 patients) are presented. The
mean distance between the NBS hotspots and the DCS hotspots was 9 mm, the mean distance
between the centres of fMRI activity and the DCS hotspots was 16 mm.
Conclusion
Using NBS, nTMS results are closer to monopolar DCS results than fMRI and, taking into account al
error sources, the agreement between nTMS and DCS results is as close as one can practical y
achieve. nTMS seems to be a powerful method for preoperative planning as wel as providing
preoperative estimation of direct cortical stimulation locations. With nTMS, the decision to perform
surgery on a patient previously not considered for resection can be made, and straightforward
surgical planning can be achieved.
Case presentation: Peritumoral mapping with NBS. No fMRI data available from M1 areas close to the tumour margin. Published in: Abstracts from the 1st. International Workshop on Navigated Brain Stimulation in Neurosurgery, 5-6; March 1, 2010

Source: http://www.nexstim.de/doc/goethe-uni-abstract.pdf