Volumetric assessment of tumor infiltration of adjacent white matter based on anatomic MRI and diffusion tensor tractography

Abstract

Rationale and objectives: To perform a retrospective, quantitative assessment of the anatomic relationship between intra-axial, supratentorial, primary brain tumors, and adjacent white matter fiber tracts based on anatomic and diffusion tensor magnetic resonance imaging (MRI). We hypothesized that white matter infiltration may be common among different types of tumor.

Material and methods: Preoperative, anatomic (T1- and T2-weighted), and LINESCAN diffusion tensor MRI were obtained in 12 patients harboring supratentorial gliomas (World Health Organization [WHO] Grades II and III). The two imaging modalities were rigidly registered. The tumors were manually segmented from the T1- and T2-weighted MRI, and their volume calculated. A three-dimensional tractography was performed in each case. A second segmentation and volume measurement was performed on the tumor regions intersecting adjacent white matter fiber tracts. Statistical methods included summary statistics to examine the fraction of tumor volume infiltrating adjacent white matter.

Results: There were five patients with low-grade oligodendroglioma (WHO Grade II), one with low-grade mixed oligoastrocytoma (WHO Grade II), one with ganglioglioma, two with low-grade astrocytoma (WHO Grade II), and three with anaplastic astrocytoma (WHO Grade III). We identified white matter tracts infiltrated by tumor in all 12 cases. The median tumor volume (+/- standard deviation) in our patient population was 42.5 +/- 28.9 mL. The median tumor volume (+/- standard deviation) infiltrating white matter fiber tracts was 5.2 +/- 9.9 mL. The median percentage of tumor volume infiltrating white matter fiber tracts was 21.4% +/- 9.7%.

Conclusions: The information provided by diffusion tensor imaging combined with anatomic MRI might be useful for neurosurgical planning and intraoperative guidance. Our results confirm previous reports that extensive white matter infiltration by primary brain tumors is a common occurrence. However, prospective, large population studies are required to definitively clarify this issue, and how infiltration relates to histologic tumor type, tumor size, and location.

Figure 1

Left frontal Oligodendroglioma WHO II. A: post-contrast, axial 3D-SPGR; B: axial T2-FSE; C: coronal view at the level of the posterior limb of the internal capsule; 2D-DT-MRI visualization overlaid on the corresponding T2-weighed baseline slice (the lines represent the in-plane fibers, whereas the through-plane fibers are represented as yellow dots); note the tumor infiltration of descending fibers (arrows); D: coronal view at a level located posterior from the slice in Figure 1C; fiber tracts in this area are displaced by the tumor mass (arrowheads).

Figure 2

Right temporal ganglioglioma. A: axial 3D-SPGR; B: axial T2-FSE; the tumor exerts mass effect on the right cerebral peduncle and right optic tract (arrows); C: 3D-tractography registered with the 3D-SPGR scan; corticospinal fibers (yellow) traversing the medial aspect of the tumor; red: manual segmentation of the tumor mass; green: manual segmentation of the tumor region intersected by corticospinal fibers.

Figure 3

Left fronto-temporal Oligodendroglioma WHO II. A: axial T2-FSE; B: color-coded 2D-DT-MRI visualization overlaid on the corresponding T2-weighted slice; the tumor is outlined in dark green; areas of high fractional anisotropy (light-blue lines) within the tumor confines, corresponding to infiltrated white matter fibers, are outlined in red; C: 3D-tractography overlaid on the baseline T2-weighted acquisition (left lateral view); note the uncinate fasciculus (arrows) running through the T2-hyperintense tumor mass.