Peritumoral diffusion tensor imaging of high-grade gliomas and metastatic brain tumors

Abstract

Background and purpose: Diffusion tensor imaging (DTI) is an advanced MR technique that describes the movement of water molecules by using two metrics, mean diffusivity (MD), and fractional anisotropy (FA), which represent the magnitude and directionality of water diffusion, respectively. We hypothesize that alterations in these values within the tissue surrounding brain tumors reflect combinations of increased water content and tumor infiltration and that these changes can be used to differentiate high-grade gliomas from metastatic lesions.

Methods: DTI was performed in 12 patients with high-grade gliomas and in 12 with metastatic lesions. DTI measurements were obtained from regions of interest (ROIs) placed on normal-appearing white matter and on the vasogenic edema, the T2 signal intensity abnormality surrounding each tumor.

Results: The peritumoral region of both gliomas and metastatic tumors displayed significant increases in MD (P <.005) and significant decreases in FA (P <.005) when compared with those of normal-appearing white matter. Furthermore, the peritumoral MD of metastatic lesions measured significantly greater than that of gliomas (P <.005). Peritumoral FA measurements, on the other hand, showed no such discrepancy.

Conclusion: When compared with an internal control, diffusion metrics are clearly altered within the vasogenic edema surrounding both high-grade gliomas and metastatic tumors, reflecting increased extracellular water. Although peritumoral MD can be used to distinguish high-grade gliomas from metastatic tumors, peritumoral FA demonstrated no statistically significant difference. The FA changes surrounding gliomas, therefore, can be attributed not only to increased water content, but also to tumor infiltration.

Fig 1.

Images in a patient with lung carcinoma. A, Contrast-enhanced T1-weighted MR image demonstrates an enhancing mass adjacent to the central sulcus on the right side. B, ROIs are placed within the hyperintense vasogenic edema on this T2-weighted MR image and within the corresponding contralateral white matter. C, MD overlay map renders a mean MD of 0.908 × 10⁻³ mm²/s. D, FA overlay map renders a mean FA of 0.114. The peritumoral DTI metrics are consistent with lung metastasis.

Fig 2.

Scatterplot of FA versus MD demonstrates lack of high correlation between the two variables (R = −0.70). The data in the metastasis group tend to lie within the higher range of MD, when compared with the data in the glioma group (P < .005). Along the FA axis, no such statistically significant discrepancy was observed.

Fig 3.

Images in a patient with glioblastoma multiforme. A, Contrast-enhanced T1-weighted MR image demonstrates an enhancing mass in the left temporal lobe that is not clearly high-grade glioma nor clearly metastasis on this conventional MR image. B, ROIs are placed within the hyperintense vasogenic edema on a T2-weighted MR image and within the corresponding contralateral white matter. C, MD overlay map renders a mean MD of 0.603 × 10⁻³ mm²/s. D, FA overlay map renders a mean FA of 0.301. The peritumoral DTI metrics are consistent with glioblastoma multiforme.

Fig 4.

Schematics illustrate the factors behind the comparable change in peritumoral FA. A, Water content and axonal disorganization contributing to decreased FA. B, Water content contributing to decreased FA