Improved delineation of glioma margins and regions of infiltration with the use of diffusion tensor imaging: an image-guided biopsy study

Abstract

Background and purpose: The efficacy of radiation therapy, the mainstay of treatment for malignant gliomas, is limited by our inability to accurately determine tumor margins. As a result, despite recent advances, the prognosis remains appalling. Because gliomas preferentially infiltrate along white matter tracks, methods that show white matter disruption should improve this delineation. In this study, results of histologic examination from samples obtained from image-guided brain biopsies were correlated with diffusion tensor images.

Methods: Twenty patients requiring image-guided biopsies for presumed gliomas were imaged preoperatively. Patients underwent image-guided biopsies with multiple biopsies taken along a single track that went into normal-appearing brain. Regions of interest were determined from the sites of the biopsies, and diffusion tensor imaging findings were compared with glioma histology.

Results: Using diffusion tissue signatures, it was possible to differentiate gross tumor (reduction of the anisotropic component, q > 12% from contralateral region), from tumor infiltration (increase in the isotropic component, p > 10% from contralateral region). This technique has a sensitivity of 98% and specificity of 81%. T2-weighted abnormalities failed to identify the margin in half of all specimens.

Conclusion: Diffusion tensor imaging can better delineate the tumor margin in gliomas. Such techniques can improve the delineation of the radiation therapy target volume for gliomas and potentially can direct local therapies for tumor infiltration.

Fig 1.

An example of the biopsy findings from a region of tumor in a 41-year-old man who presented with seizures and a mild left hemiparesis. The T2-weighted image shows that the biopsy was taken from the center of the lesion and that histologic examination (above right) confirmed it as a WHO grade III anaplastic oligoastrocytoma. The tissue signature from this region shows significant increase in p (10% compared with normal side) with a significant decrease in q (12%).

Fig 2.

Biopsy from a region 2.5 cm from the target of Fig 1. The T2-weighted image shows it has been taken from a region that is apparently normal. Histologic examination, however, confirms normal white matter with tumor infiltration. The tissue signature in this region shows a significant increase in p without much change in q.

Fig 3.

Biopsies taken from 3.5 cm from the target of the patient in Figure 1. Both MR and histology show that this is from normal brain. The tissue signatures from this region show that both the p value and q values are similar to control values.

Fig 4.

A gadolinium-enhanced T1-weighted (left) and T2-weighted (right) image from a 67-year-old man who presented with headaches and a left hemiparesis. Our results have shown that we can identify a region around a tumor with decreased anisotropy (q, shown in green) that shows the limit of the gross tumor, and a region around this with normal anisotropy but increased isotropy (p, shown in red) that can identify the infiltrating tumor margin. These zones extend beyond the abnormal areas on both enhanced T1- and T2-weighted MRI