gms | German Medical Science

Objective: Despite all limitations diffusion tensor imaging (DTI) is the only technique available today to illustrate subcortical white matter pathways and therefore has been implemented in presurgical workup for brain tumor surgery. Aim of the present study was to compare pre- and intraoperatively acquired DTI data in order to analyze brain shift of the CST. Furthermore pre- and intraoperative DTI data were validated using intermittent (monopolar electrode) and continuous (suction device with monopolar electrode) subcortical electrical stimulation in a subset of patients.

Method: A total of 25 patients were assessed. Pre- and intraoperative fiber tracts of CST were generated using a deterministic approach (ROI cerebral peduncle and posterior limb of internal capsule, FA threshold 0.15, minimum fiber length 10 mm, Brainlab iPlan 3.0). Subcortical stimulation was performed either with a dedicated monopolar electrode or a combined suction-electrode device allowing continuous subcortical mapping during resection.

Results: The majority of patients were treated for glioma (N=19, 76%). Pre and intraoperative DTI was feasible in all cases, although quality of intraoperative diffusion MRI was hampered by large craniotomies with broad brain air interphase. Significant brain shift was observed in all patients depending on patients positioning, localization and size of tumor. Shifting of the corticospinal tract was most likely observed at the level of the posterior limb of the internal capsule and above at the semioval center. In 11 patients the location of cortico-spinal tract was verified by subcortical stimulation which showed good correlation with intraoperative DTI update and confirmed the brainshift of the fibertract due to surgical manipulation.

Conclusions: Diffusion MRI with tractography is useful for preoperative illustration of dislocation of fiber tracts. Due to brainshift fiber objects generated on the basis of preoperative data should never guide radicality of brain tumor surgery. Quality of intraoperative DTI is hampered by artefacts especially in large craniotomies but enable compensation of intraoperative brain shift in most of the cases. Subcortical stimulation confirmed dislocation of CST during tumor resection. Therefore in the future, intraoperative DTI as an adjunct to continuous subcortical mapping might be a tool to further improve onco-functional balance in brain tumor surgery.