Diffusion-tensor MR imaging of intracranial neoplasia and associated peritumoral edema: introduction of the tumor infiltration index.

PURPOSE: To determine whether diffusion-tensor magnetic resonance (MR) imaging metrics of peritumoral edema can be used to differentiate intra- from extraaxial lesions, metastatic lesions from gliomas, and high- from low-grade gliomas.

MATERIALS AND METHODS: In this study, diffusion-tensor MR imaging was performed preoperatively in 40 patients with intracranial neoplasms, including meningiomas, metastatic lesions, glioblastomas multiforme, and low-grade gliomas. Histograms of mean diffusivity (MD) and fractional anisotropy (FA) were used to analyze both the tumor and the associated T2 signal intensity abnormality. An additional metric, the tumor infiltration index (TII), was evaluated. The TII is a measure of the change in FA presumably caused by tumor cells infiltrating the peritumoral edema. Student t test and least-squares linear regression analyses were performed.

RESULTS: Peritumoral MD and FA values indicated no statistically significant difference between intra- and extraaxial lesions or between high- and low-grade gliomas. Regarding intraaxial tumors, the measured mean peritumoral MD of metastatic lesions, 0.733 x 10(-3) mm(2)/sec +/- 0.061 (SD), was significantly higher than that of gliomas, 0.587 +/- 0.093 x 10(-3) mm(2)/sec (P <.05). There was also a statistically significant difference between the TIIs of the edema surrounding meningiomas and metastases (mean, 0 +/- 35) and the TIIs of the edema surrounding gliomas (mean, 64 +/- 59) (P <.05).

CONCLUSION: Peritumoral diffusion-tensor MR imaging metrics enable the differentiation of solitary intraaxial metastatic brain tumors from gliomas. In addition, the TII enables one to distinguish presumed tumor-infiltrated edema from purely vasogenic edema.