gms | German Medical Science

Objective: The introduction of Magnetic Resonance Diffusion Tensor Imaging (DTI) enables the construction of virtual fiber tracts. Due to the severe impact of intraoperative damage, the integration of the corticospinal tract into neurosurgical planning and navigation systems is of special interest and becomes more and more part of the clinical routine. Nevertheless, little is known as to which extent these reconstructions created by mathematic algorithms really do display the existing morphological and physiological structures.

Methods: Diffusion Tensor Imaging was performed in 35 patients with tumors adjacent to the suspected corticospinal tract. We carried out fiber tracking of the corticospinal tract by a modified line-propagation algorithm and by definition of one Region of InterestROI) in the pons and one subcortically. The data was transferred to a neurosurgical navigation system and after craniotomy the DTI-depicted corticospinal tract was compared to the corticospinal tract investigated by cortical (SEP-phase revearsal and Motor Evoked Potentials) and subcortical (Motor Evoked Potentials) electrophysiology.

Results: In all 35 patients, intraoperative neurophysiology including SEP phase revearsal, cortical and/or subcortical stimulation was performed. In 31 cases, the via fiber tracking which depicted the virtual origin of the corticospinal tract could be confirmed by cortical stimulation. In 22 patients subcortical stimulation of the pyramidal tract was performed during and at the end of the operative procedure. In 20 of those 22 patients the depicted virtual corticospinal tract was in accordance with neurophysiological testing. Negative results were partly due to seizures provoked during stimulation.

Conclusions: The ability of DTI-based fiber tracking to detect the localisation of the corticospinal tract could be confirmed by intraoperative neurophysiology in the vast majority of patients. DTI-based fiber tracking may so help to minimize traumatization during brain surgery. In the presented cases direct stimulation of the corticospinal tract gave evidence that in case of evoked responses the virtual fiber tract is within a minimum of 15 mm - more probably within 5 mm. Taking into account different possible inaccurancies from DTI-acquisition to brain-shift and the observation that already surgical damage of less than one centimeter within the white matter tract can lead to severe permanent deficit, surgery near the motor pathways should continue to be combined with the conduction of continous (cortical) motor evoked potentials.