Diffusion-weighted MR imaging of intracerebral masses: comparison with conventional MR imaging and histologic findings

Abstract

Background and purpose: The purposes of this study were to find the role of diffusion-weighted MR imaging in characterizing intracerebral masses and to find a correlation, if any, between the different parameters of diffusion-weighted imaging and histologic analysis of tumors. The usefulness of diffusion-weighted imaging and apparent diffusion coefficient (ADC) maps in tumor delineation was evaluated. Contrast with white matter and ADC values for tumor components with available histology were also evaluated.

Methods: Twenty patients with clinical and routine MR imaging/CT evidence of intracerebral neoplasm were examined with routine MR imaging and echo-planar diffusion-weighted imaging. The routine MR imaging included at least the axial T2-weighted fast spin-echo and axial T1-weighted spin-echo sequences before and after contrast enhancement. The diffusion-weighted imaging included an echo-planar spin-echo sequence with three b values (0, 300, and 1200 s/mm(2)), sensitizing gradient in the z direction, and calculated ADC maps. The visual comparison of routine MR images with diffusion-weighted images for tumor delineation was performed as was the statistical analysis of quantitative diffusion-weighted imaging parameters with histologic evaluation.

Results: For tumors, the diffusion-weighted images and ADC maps of gliomas were less useful than the T2-weighted spin-echo and contrast-enhanced T1-weighted spin-echo images in definition of tumor boundaries. Additionally, in six cases of gliomas, neither T2-weighted spin-echo nor diffusion-weighted images were able to show a boundary between tumor and edema, which was present on contrast-enhanced T1-weighted and/or perfusion echo-planar images. The ADC values of solid gliomas, metastases, and meningioma were in the same range. In two cases of lymphomas, there was a good contrast with white matter, with strongly reduced ADC values. For infection, the highest contrast on diffusion-weighted images and lowest ADC values were observed in association with inflammatory granuloma and abscess.

Conclusion: Contrary to the findings of previous studies, we found no clear advantage of diffusion-weighted echo-planar imaging in the evaluation of tumor extension. The contrast between gliomas, metastases, meningioma, and white matter was generally lower on diffusion-weighted images and ADC maps compared with conventional MR imaging. Unlike gliomas, the two cases of lymphomas showed hyperintense signal on diffusion-weighted images whereas the case of cerebral abscess showed the highest contrast on diffusion-weighted images with very low ADC values. Further study is required to find out whether this may be useful in the differentiation of gliomas and metastasis from lymphoma and abscess.

fig 1.

Images from the case of a 34-year-old man with a large grade II astrocytoma in the inferior frontal and parietal area. Differentiation between edema and tumor is unclear on all sequences. A, Fast T2-weighted spin-echo image. B, Contrast-enhanced T1-weighted spin-echo image. The stereotactic biopsy was performed in the area of faint contrast material uptake (arrow). C, Diffusion-weighted echo-planar image acquired with x sensitizing gradient. D, Diffusion-weighted echo-planar image acquired with y sensitizing gradient. E, Diffusion-weighted echo-planar image acquired with z sensitizing gradient. F, Tensor ADC map. G, Lattice index map. The red/yellow areas represent high/medium anisotropy, and the blue/dark blue areas represent lower anisotropy

fig 2.

Images from the case of a 52-year-old man with a large glioblastoma. A, Invasion of corpus callosum and of occipitotemporal white matter is recognized on fast T2-weighted spin-echo image. B, Invasion of corpus callosum and of occipitotemporal white matter is recognized on contrast-enhanced T1-weighted spin-echo image. C, Invasion of subinsular white matter is clearly recognized only on the perfusion-weighted echo-planar image (arrow). D, On the diffusion-weighted image, only cystic components of tumor are clearly shown. There is no clear difference between contrast-enhancing tumor (arrowhead) and edema (arrow). E, On the ADC map, only cystic components of tumor are clearly shown. There is no clear difference between contrast-enhancing tumor (arrowhead) and edema (arrow). F, Histologic examination (hematoxylin and eosin; original magnification, ×250) shows a medium sized extracellular space and moderate cellularity

fig 2.

fig 3. Images from the case of a 72-year-old woman with a cerebral lymphoma. A, Fast T2-weighted spin-echo image shows lesion to be moderately hyperintense. B, T1-weighted spin-echo image shows strong enhancement of lesion after the administration of contrast material. C, Diffusion-weighted image shows the lymphoma also to be hyperintense. D, ADC values are in the range of 0.55 to 0.6, similar to the values described in association with acute infarction. E, Histologic examination (hematoxylin and eosin; original magnification, ×250) shows high cellularity and small extracellular space, which was significantly associated with reduced ADC values

fig 4.

Images from the case of a 70-year-old man with a streptococcus abscess, recent history of acute dizziness, and focal seizures. A, T2-weighted spin-echo image is consistent with the diagnosis of glioblastoma or necrotic metastasis. B, Contrast-enhanced T1-weighted spin-echo image is consistent with the diagnosis of glioblastoma or necrotic metastasis. C, On the diffusion-weighted echo-planar image, however, the “necrotic” area shows high signal intensity (arrow). D, On the ADC map, very low ADC values (0.29 e⁻³ mm²/s) are found (arrow). Such behavior was never present in the necrotic parts of gliomas (compare with fig. 3D and E) or metastases and may be highly specific for abscess formation