Artikel
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
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Autoren
Veröffentlicht: | 23. April 2004 |
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Gliederung
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Objective
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.
Methods
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.
Results
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).
Conclusions
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.