Preoperative Multi-modal Motor Mapping: A Comparison of Magnetic Source Imaging, Navigated Transcranial Magnetic Stimulation, and Direct Cortical Stimulation

Phiroz Erach Tarapore, MD1, Matthew Tate, MD1, Anne Findlay1, Susanne Honma1, Danielle Mizuiri1, Mitchel Berger, MD1

1San Francisco, CA United States

Keywords: cortical mapping, technique, magnetic resonance imaging, monitoring, complications

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Abstract

     Direct cortical stimulation (DCS) is the gold-standard technique for motor mapping during craniotomy. However, preoperative motor mapping is becoming increasingly accurate. Two such modalities are navigated transcranial magnetic stimulation (nTMS) and magnetic source imaging (MSI). While MSI has been extensively validated in this context, TMS is less well studied.
     Here, we compare the accuracy of nTMS to both DCS and to MSI.
     Patients with tumors in proximity to primary motor cortex underwent pre-operative nTMS and MSI for motor mapping.
     They subsequently went to surgery, where they underwent motor mapping via intraoperative DCS. The loci of maximal response were recorded from each modality and compared. Motor strength was assessed at 3 months postoperatively.
     nTMS and MSI were performed on 24 patients. Intraoperative DCS yielded 8 positive motor sites in 5 patients. The median distance ±SEM between nTMS and DCS motor sites was 2.1 ± 0.29mm; between nTMS and MSI motor sites it was 4.71 ± 1.08mm. In no patients did DCS motor mapping reveal a motor site that was unrecognized by nTMS. Three of 24 patients had new, early neurological deficit in the form of upper extremity paresis. At 3-months follow-up, two of these patients were significantly improved, experiencing difficulty only with fine motor tasks; the remaining patient had improvement to 4/5 strength.
     This is a retrospective study.
     Maps of the motor system generated with nTMS correlate well with those generated by MSI and DCS.
     Negative nTMS mapping also correlates with negative DCS mapping. nTMS is an accurate modality for generating preoperative motor maps noninvasively.


Acknowledgements

Project Roles:

P. Tarapore (), M. Tate (), A. Findlay (), S. Honma (), D. Mizuiri (), M. Berger ()