The role of diffusion-weighted imaging in patients with brain tumors

Abstract

Background and purpose: Diffusion-weighted images (DWIs) have been used to study various diseases, particularly since echo-planar techniques shorten examination time. Our hypothesis was that DWIs and tumor apparent diffusion coefficients (ADCs) could provide additional useful information in the diagnosis of patients with brain tumors.

Methods: Using a 1.5-T MR unit, we examined 56 patients with histologically verified or clinically diagnosed brain tumors (17 gliomas, 21 metastatic tumors, and 18 meningiomas). We determined ADC values and signal intensities on DWIs both in the solid portion of the tumor and in the peritumoral, hyperintense areas on T2-weighted images. We also evaluated the correlation between ADC values and tumor cellularity in both gliomas and meningiomas.

Results: The ADCs of low-grade (grade II) astrocytomas were significantly higher (P =.0004) than those of other tumors. Among astrocytic tumors, ADCs were higher in grade II astrocytomas (1.14 +/- 0.18) than in glioblastomas (0.82 +/- 0.13). ADCs and DWIs were not useful in determining the presence of peritumoral neoplastic cell infiltration. The ADC values correlated with tumor cellularity for both astrocytic tumors (r = -.77) and meningiomas (r = -.67).

Conclusion: The ADC may predict the degree of malignancy of astrocytic tumors, although there is some overlap between ADCs of grade II astrocytomas and glioblastomas.

fig 1.

Glioblastoma in the right temporal lobe. A, T2-weighted image showing tumor of mixed intensity (from low to high) with peritumoral edema. B, The tumor shows heterogeneous enhancement after intravenous injection of contrast medium. C, On DWI, a solid portion of the tumor is isointense to moderately high in intensity, and edema is isointense. D, The ADC map calculated from DWI. Small circles from 1 to 12 in the right medial temporal lobe indicate the regions of interest (which are too small to be seen).

fig 2.

Grade II astrocytoma in the left insular portion. A, Tumor shows high intensity on a T2-weighted image. B, No enhancement is seen on a T2-weighted image. C, On DWI, the tumor is isointense to mildly hyperintense. D, On the ADC map, representative regions of interest are shown (small circles).

fig 3.

Tumor in the right occipital lobe, metastasized from the lung. A, On a T2-weighted image, the solid portion of the tumor is mildly hyperintense, and peritumoral edema is present anterior to the tumor. B, Tumor shows relatively homogeneous enhancement after injection of contrast medium. C, On DWI, the solid portion of the tumor is isointense to mildly high in intensity. D, Regions of interest are shown (small circles) on the ADC map. The ADC values are 0.80, 0.74, 0.68, and 0.67, and the averaged ADC value is 0.72. Apparent restricted diffusion (high signal) in the tumor periphery appears to reflect T2 shine-through effect, although peripheral high intensity is not seen on the T2-weighted image.

fig 4.

Meningothelial meningioma in the left high frontal convexity. A, On a T2-weighted image, tumor is mildly high in intensity. B, Tumor enhances homogeneously on a T2-weighted image. C, The tumor is of high intensity on DWI. D, Regions of interest are shown on the ADC map. The ADC values are 0.76, 0.63, and 0.55, and the averaged ADC value is 0.65. Restricted diffusion in the tumor probably is caused by high tumor cellularity.

fig 5.

Fibrous meningioma in the left convexity. A, On a T2-weighted image, tumor intensity is mildly high and edema is present anterior to the tumor. B, The tumor enhances homogeneously. C, On DWI, the peripheral portion of the tumor is moderately hyperintense and the central portion is isointense. Peritumoral edema is mildly high in intensity. D, Regions of interest are shown on the ADC map. The ADC values are 0.83, 0.74, 0.71, 0.67, and 0.57, and the averaged ADC value is 0.70. Some areas of apparent restricted diffusion in the tumor probably reflect T2 shine-through effect, because ADC values in these areas are not low and the signals in those areas show high intensity on the T2-weighted image.

fig 6.

The ADCs of tumor for glioblastomas, grade II astrocytomas, metastatic tumors, and meningiomas. The ADCs of astrocytomas are higher than those of other tumors, while ADCs of glioblastomas are lower than those of grade II astrocytomas.fig 7. The ADCs of each histologic type of meningioma. No significant difference is present among histologic types

fig 8.

A correlation (r =−.77) is observed between tumor cellularity and ADC values of astrocytic tumors.fig 9. A correlation (r =−.67) is observed between tumor cellularity and ADC values of meningiomas