gms | German Medical Science

Objective: Navigated TMS (nTMS) is evolving as a reliable method for analysis of cortical motor representation in the vicinity of rolandic tumors. White matter tractography by DTI is under intense investigation as a method for selective visualization of fiber tracts. Definite selection of the seed region of interest (ROI) from which fiber tracking begins can be compromised in cases of rolandic tumors with severe mass effect. We propose to select the seed points based on the nTMS activation map to enable a comprehensive mapping of cortical and subcortical motor function preoperatively.

Methods: In a series of 10 patients with tumors of the central region and marked distortion of sulcal and subcortical anatomy nTMS was performed preoperatively. The cortical representation of the abductor pollicis brevis muscle was determined and subsequently used as the primary cortical seed ROI for performance of DTI. The results of both examinations were implemented into the neuronavigation unit to faciliate comparison with the results of the navigated direct electrocortical stimulation.

Results: nTMS enabled a detailed mapping of the primary motor cortex despite significant distortion of the sulcal antomy. Utilizing the nTMS results for initiating DTI allowed performing successful tractography in all cases. Direct electrocortical stimulation demonstrated a high degree of congruence to the non-invasive results. We observed transient hemiparesis in 6 cases and a permanent paresis in one case, in which DTI had demonstrated immediate proximity of pyramidal tract and tumor.

Conclusions: The combination of nTMS with DTI allowed for a accurate definition of the seed ROI for DTI based tractography. This approach provides a comprehensive, functionally related, cortical and subcortical motor mapping even in cases of Rolandic tumors with severe mass effect.