Diffusion tensor imaging of brainstem tumors: axonal degeneration of motor and sensory tracts

Object. Diffusion tensor (DT) imaging has been used to predict postoperative motor function in patients with supratentorial tumors. The authors sought to determine whether DT imaging and white matter tractography could detect axonal degeneration in patients with brainstem tumors. Methods. A cross-sectional, retrospective study of 7 patients with brainstem tumors and 8 healthy volunteers was performed. The DT imaging data were normalized and regions of interest (ROIs) with the highest probability of sensory and motor connections were selected using the Talairach Atlas to identify the 3D millimetric coordinates of white matter tracts. An iterative process involving fractional anisotropy (FA), apparent diffusion coefficients (ADCs), and color maps was developed to precisely select ROIs in the bilateral sensory and motor tracts. The FA and ADC values were calculated for each ROI. Results. The FA values of sensory and motor tracts significantly differed between the patient and healthy volunteer groups (p < 0.05), whereas no significant changes were found in the splenium or genu of the corpus callosum. The FA values were altered proximal and distal to the brainstem tumors with a bimodal peak of antegrade decreased FA involving second- and third-order sensory axons and retrograde decreased FA of motor axons. Conclusions. This study demonstrates changes in diffusion properties of sensory and motor tracts consistent with degeneration to further characterize brainstem tumors in children, and the results warrant the planning of prospective trials. The rigorous methods the authors describe may provide valuable information when planning biopsies or debulking of unusual brainstem tumors, as well as improve prognostication of the possible functional tract recovery following therapy.