Functional activity within brain tumors: A magnetic source imaging study

OBJECTIVE: To determine whether low-grade gliomas contain functional cortic al activity more often than high-grade gliomas within radiologically define d abnormal tissue. METHODS: Patients with intra-axial cerebral lesions located in the vicinity of eloquent brain cortex preoperatively underwent magnetic source imaging. A dual 37-channel biomagnetometer was used to perform the imaging. Evoked magnetic fields were analyzed using the single-equivalent dipole representa tion to ascertain the neuronal source. Stimuli included painless tactile so matosensory stimulation of fingers, toes, and lips and auditory presentatio n of pure sinusoidal tones. RESULTS: A retrospective analysis of 106 nonconsecutively treated patients, who had undergone preoperative magnetic source imaging between February 19 96 and December 1999, revealed that 24.5% of the patients had been at risk for neurological deficits, because functionally active tissue was located w ithin or at the border of the tumor. Functional activity was found within t he radiologically defined lesion in 18% of Grade 2 tumors, in 17% of Grade 3 tumors, and in 8% of Grade 4 tumors. CONCLUSION: The results confirm that, regardless of tumor grade, intra-axia l brain tumors may involve or directly border on functional cortex. The deg ree of involvement of functionally viable cortex appeared greater for low-g rade tumors than for high-grade lesions. On the other hand, high-grade lesi ons were more likely to be associated with functional cortex at their margi ns or within peritumoral edema. To safely maximize tumor resection, preoper ative functional imaging and intraoperative electrophysiological mapping of the cerebral cortex and the white matter tracts are deemed necessary.