BACKGROUND: Primary brain tumors in motor eloquent areas are associated with high-risk surgical procedures because of potentially permanent and often disabling motor deficits. Intraoperative primary motor cortex mapping and corticospinal tract (CST) monitoring are well-developed and reliable techniques. Imaging of the CST by diffusion tensor tractography (DTT) is also feasible.
OBJECTIVE: To evaluate the practical value of 3.0T intraoperative MRI (iMRI) with intraoperative DTT (iDTT) in surgery close to the CST, and to compare high-field iDTT with intraoperative neurophysiological CST mapping during glioma and metastasis resection in a routine setting.
METHODS: Twenty-five patients (13 males, 12 females, median 47 years) were enrolled prospectively from June 2010 to June 2012. Patients were included if they had a solitary supratentorial intracerebral lesion compressing or infiltrating the CST according to preoperative MRI. Subcortical CST mapping was performed by monopolar (cathodal) stimulation (500 Hz, 400 μs, 5 pulses). CST DTT was made both at preoperative and intraoperative 3.0T MRI. Subcortical motor-evoked potential threshold current and probe-CST distance were recorded at 155 points before and at 103 points after iMRI. Current-distance correlations were performed both for pre-iMRI and for post-iMRI data.
RESULTS: The correlation coefficient pre-iMRI was R = 0.470 (P < .001); post-iMRI, the correlation coefficient was R = 0.338 (P < .001). MRI radical resection was achieved in 17 patients (68%), subtotal in 5 (24%), and partial in 3 (12%). Postoperative paresis developed in 8 patients (32%); the paresis was permanent in 1 case (4%).
CONCLUSION: The linear current-distance correlation was found both in pre-iMRI and in post-iMRI data. Intraoperative image distortion appeared in 36%. Neurophysiological subcortical mapping remains superior to DTT. Combining these 2 methods in selected cases can help increase the safety of tumor resection close to the CST.
ABBREVIATIONS: cont-MEP, continuous motor-evoked potentials
CRDT, complete resection of detectable tumor
CRET, complete resection of enhancing tumor
CS, central sulcus
CST, corticospinal tract
DTI, diffusion tensor imaging
DTT, diffusion tensor tractography
FOV, field of view
FSPGR, fast spoiled gradient-recall-echo
iDTT, intraoperative diffusion tensor tractography
iMRI, intraoperative magnetic resonance imaging
iPT, intraoperative pyramidal tract
iUS, intraoperative ultrasound
MEP, motor-evoked potential
NEX, number of excitations
PMC, primary motor cortex
Post-Dist, distances measured after iMRI
Pre-Dist, distances measured before iMRI
PT, pyramidal tract
scMEP, subcortical motor-evoked potential
SEP, somatosensory-evoked potential
SNR, signal-to-noise ratio
WHO, World Health Organization