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55. Jahrestagung der Deutschen Gesellschaft für Neurochirurgie e. V. (DGNC)
1. Joint Meeting mit der Ungarischen Gesellschaft für Neurochirurgie

Deutsche Gesellschaft für Neurochirurgie (DGNC) e. V.

25. bis 28.04.2004, Köln

Pre-existing mMEP alterations detected by simultaneous bicortical electrical stimulation and growth pattern of supratentorial tumors

Detektion präexistenter mMEP-Veränderungen durch simultane bikortikale elektrische Stimulation und deren Abhängigkeit vom Wachstumsmuster supratentorieller Tumore

Meeting Abstract

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  • corresponding author Alf Giese - Department of Neurosurgery, University of Schleswig-Holstein, Campus Lübeck, Lübeck
  • D. Wertheimer - Department of Neurosurgery, University of Hamburg
  • M. Westphal - Department of Neurosurgery, University of Hamburg

Deutsche Gesellschaft für Neurochirurgie. Ungarische Gesellschaft für Neurochirurgie. 55. Jahrestagung der Deutschen Gesellschaft für Neurochirurgie e.V. (DGNC), 1. Joint Meeting mit der Ungarischen Gesellschaft für Neurochirurgie. Köln, 25.-28.04.2004. Düsseldorf, Köln: German Medical Science; 2004. DocDI.02.02

The electronic version of this article is the complete one and can be found online at:

Published: April 23, 2004

© 2004 Giese et al.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( You are free: to Share – to copy, distribute and transmit the work, provided the original author and source are credited.




Pre-existing alterations of myogenic motor evoked potentials (mMEP) in supratentorial lesions may indicate a higher vulnerability. In this study we have analyzed the influence of tumor growth pattern on mMEP asymmetries detected by electrical bicortical stimulation.


In 22 patients with gliomas near eloquent motor areas mMEP were elicited by transcranial stimulation with a bilateral symmetrical electrical field after induction of narcosis prior to tumor dissection. Nineteen patients had a normal motor function, three patients presented with a hemiparesis.


mMEP registration demonstrated asymmetrical amplitudes ≥50% in 11 (of 19) patients with no pre-existing motor deficit and in all patients with a motor deficit. In all cases the lower amplitudes corresponded to the site of the lesion. To analyze the influence of the tumor growth on mMEP asymmetries preoperative MRI scans were evaluated for involvement of the motor pathways. This demonstrated that asymmetry of mMEP amplitudes > 50% was associated with a significant degree of space occupation. In no case was a none-space occupying infiltrative lesion associated with mMEP asymmetry. Space occupation was positively correlated with the degree of mMEP amplitude asymmetry (r=0.87, P<0.0001). No association of signal abnormality indicating edema and/or infiltration with mMEP asymmetries was found (r=0.00, P = 1.00).


mMEP asymmetries are a result of compression of motor structures. Resection of a space occupying lesion in some cases lead to the improvement of mMEP amplitudes, indicating that asymmetries may not be due to structural lesions. Infiltrative tumor growth does not result in a functional deficit detected by mMEP elucidation.