Sarah Goldfeder, MD, and P-L Westesson, MD, PhD, DDS
Clinical
Presentation: An
87-year-old male presented with one week of progressive slurred speech and visual changes.
Imaging Findings: Brain MR: T1-weighted images with contrast (Fig. 1) demonstrate a large, solitary, enhancing mass-lesion in the left occipital lobe. There is a thick rim of intense enhancement and a large central area of necrosis. FLAIR images show significant edema involving the white matter in the left cerebral hemisphere (Fig. 2).
Perfusion images (Fig. 3) show markedly increased regional cerebral blood volume (RCBV) in the enhancing portion of the lesion. The maximum RCBV ratio of the lesion to the contralateral normal-appearing white matter is elevated to approximately 9.
MR spectroscopy (Fig. 4) demonstrates an increased choline peak, a moderately decreased NAA peak, and an increased lipid peak. The choline/creatine ratio is approximately 1.5.
MR with fiber tracking (Fig. 5) shows medial displacement of neuronal tracks. There is also truncation of fibers, suggesting diffuse infiltration into the lesion.
Figure 1: T1-weighted with contrast. Large, solitary, enhancing mass-lesion in the left occipital lobe. Thick rim of intense enhancement and a large central area of necrosis.
Figure 2: FLAIR. Significant edema involving the white matter in the left cerebral hemisphere.
Figure 3: Perfusion. Increased regional cerebral blood volume (RCBV) in the enhancing portion of the lesion.
Figure 4: MR spectroscopy. Increased choline peak, moderately decreased NAA peak, and an increased lipid peak.
Figure 5: Diffusion tractography. Medial displacement of neuronal tracks and truncation of fibers.
Diagnosis: Glioblastoma multiforme, WHO grade IV
Discussion: Diffusion tensor imaging (DTI), an extension of diffusion MRI, can be used to perform tractography of white matter tracks, such as the corticospinal tracks. By measuring the restricted diffusion of water in tissue, the location, orientation, and direction of white matter tracts can be displayed. Anisotropy is the property of being directionally dependent. Because white matter axons and their myelin sheaths are arranged in parallel bundles, the diffusion of water can be used to generate anisotropic, orientation-dependent imaging. Tensor matrices of 3 x 3 are analyzed to yield an eigenvector that reflects the aggregate magnitude and direction of diffusion in three-dimensional space. The vectors of the tracts can be displayed with color to indicate direction, for example, red for left-right, blue for superior-inferior, and green for anterior-posterior.
DTI can be used to show the tumor’s relationship to white matter tracks and reveal if the tumor is infiltrating or deflecting the tracks. It can also be used to localize tracks for neurosurgical planning and to assess white matter development, pathology, and degeneration. It has been suggested that primary brain tumors will show infiltration of the white matter tracks on DTI, whereas metastatic brain lesions will show deflection.
In our patient, there is apparent deflection of the white matter tracks on DTI, which would seem to suggest a solitary metastatic lesion. However, there is also truncation of the tracks, which indicates infiltration of the tracks into the lesion, and supports the diagnosis of a primary brain tumor.
The appearance of the lesion on T1-weighted images with contrast and FLAIR images points to a malignant lesion: a large lesion, with a thick rim of intense enhancement, large central area of necrosis, and significant surrounding vasogenic edema. Perfusion images show markedly increased RCBV, which also supports the diagnosis of a malignant lesion.
MR spectroscopy shows an increase in the choline peak, but with a choline/creatine ratio that is lower than expected for a malignant lesion, such as GBM. This may be due to sampling outside of the lesion. Ultimately, the surgical pathology did reveal a highly malignant lesion: a glioblastoma multiforme, WHO grade IV.
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