P 185. Functional imaging of the M1 representation of the tongue, the hand and the foot in patients with eloquently localized intracerebral tumors. Discripancies and validity of navigated TMS and functional MRI results when compared to direct cortical stimulation

Abstract

Introduction Functional magnetic resonance imaging (fMRI) and neuronavigated transcranial magnetic stimulation (nTMS) may be the most commonly used techniques for non-invasive mapping of the primary motor cortex (M1). The results of both techniques differ to a certain extent. However, which mapping technique displays a more realistic map of the M1 representation still remains unclear, especially when dealing with the tongue/face representation and under pathological conditions such us presence of a brain tumor adjacent to the M1 representation. We, therefore, evaluated both methods in patients presenting with intracerebral tumors adjacent to the cortical M1 representation or associated pyramidal fiber tracks, comparing the presurgical imaging results to the gold standard of monpolar direct cortical stimulation (DCS). Material and methods To date, 20 patients with primary brain tumors and cerebral metastases adjacent to the M1 representation and associated fiber tracks were prospectively investigated by anatomical MRI including DTI, fMRI and nTMS. NTMS and fMRI measurements were performed recording the following muscle MEPs and the corresponding movement paradigms: Abductor pollicis brevis (APB)/thumb abduction, plantaris medialis (PM)/toe flexion, anterior lateral tongue (LT)/tongue movements side-to-side. Morever, monopolar direct cortical stimulation (mDCS) was performed intraoperatively, applying a train of five on the hotspots of respective M1 representation, according to the fMRI and nTMS results (N = 8 patients with reliable results, according to DCS quality and registration mismatch). Euclidean distances (ED) and standard deviations (SD) between DCS and fMRI/nTMS coordinates were calculated. For analyses, iplanNet (Brainlab), MRICron, FSL, Matlab, Excel and SPSS (PASW 18) were used. For comparisons between means, Student’s T-test was computed. Results EDs between fMRI and DCS hotspots were within the same range (APB: 14.2 ± 6.4 mm SD; PM: 11.6 ± 9.2 mm SD; LT: 10.4 ± 4.4 mm SD) as the EDs between nTMS and DCS hotspots (13.7 ± 6.0 mm SD; PM: 12.6 ± 2.9 mm SD; LT: 10.2 ± 6.8 mm SD). However, matching between nTMS/fMRI and DCS results differed remarkably in some patients. Thus, combining both presurgical mapping techniques revealed lower EDs (APB: 10.9 ± 4.9 mm SD; PM: 8.1 ± 4.3 mm SD; LT: 9.2 ± 5.4 mm SD). Even when examining patients with symptomatic epilepsy, no side effects of nTMS were observed. Conclusion Overall, our preliminary results reveal no significant difference between both methods. Further analysis and recruiting a higher number of suitable patients may show which presurgical functional mapping technique amounts to the highest validity-compared to DCS-in specific subsets of patients. Preliminary results let suggest that clinical factors such as anticonvulsant drugs, motor deficits and alertness may considerably affect the results of both mapping techniques. Which presurgical functional mapping technique-fMRI or nTMS-may be eligible for certain patients, however, still remains to be further investigated.