Diffusion tensor imaging for preoperative evaluation of tumor grade in gliomas
Introduction
Gliomas are the most common primary neoplasms of the central nervous system [1]. The prognosis for patients with high grade gliomas has remained poor despite improvements in radiation and chemotherapy [2], [3]. Accurate preoperative diagnosis of the tumor grade is important for the determination of appropriate treatment strategies [4]. Magnetic resonance (MR) spectroscopy [5], [6], [7], [8], single photon emission computed tomography [9], [10], [11], [12], [13], or positron emission tomography [9], [10], [11] have all been used for the preoperative evaluation of glioma malignancy. However, MR spectroscopy has limitations in spatial resolution and heterogeneous lesions are difficult to assess [7], whereas imaging methods using radioactive isotopes are invasive and involve handling problems.
Diffusion tensor imaging (DTI) can measure the directionality (anisotropy) and the magnitude (diffusivity) of water diffusion in vivo [14]. Fractional anisotropy (FA) and mean diffusivity (MD) are the quantitative indices for anisotropy and diffusivity, respectively [15]. The microstructural organization of the brain tissue affects the molecular motion of water. Therefore, the FA and MD reflect microstructural changes of tissue caused by damage from degenerative disease, brain ischemia and brain tumors [16], [17], [18], [19], [20], [21]. The histological diagnosis of glioma malignancy is based on the presence of nuclear heteromorphism, nuclear mitosis, endothelial proliferation, and necrosis [22]. These characteristics may affect the FA and MD values of gliomas.
This study evaluates the relationship between the findings of DTI and the histological malignancy of gliomas.
Section snippets
Patient population
This study included 41 consecutive patients (18 females and 23 males) aged 2–77 years (mean 46 years) treated at our institute between October 2000 and December 2002, who underwent DTI and had a histological diagnosis. No medical therapy was received for their tumor prior to imaging. The patient characteristics and tumor grades, using the WHO classification [23], are listed in Table 1. The study protocol was approved by the local ethical committee. All subjects gave written informed consent
Results
DTI demonstrated the tumor mass and cystic lesions in all patients. Representative FA maps and T1-weighted images with contrast medium are shown in Fig. 2. The relationships between the FA or MD values and the tumor grade are shown in Fig. 3, Fig. 4, respectively.
The FA values of grade 1 gliomas (0.150 ± 0.017) were significantly lower than those of grade 3 (0.23 ± 0.033) or grade 4 gliomas (0.229 ± 0.033) (P < 0.0001, respectively). The FA values of grade 2 gliomas (0.159 ± 0.018) were
Discussion
The primary finding of the present study was that the FA value could be used to distinguish high grade glioma from low grade glioma.
FA values have been investigated in patients with multiple sclerosis, amyotrophic lateral sclerosis, or leukoaraiosis, showing that the FA value is an indicator of the tissue damage of white matter [17], [18], [19], [20], [24]. The molecular movement of water is restricted by membranes in the brain [25]. The presence of myelinated fibers is an important factor in
Conclusion
Investigation of the relationship between DTI and histological malignancy of gliomas found that the FA value can distinguish high grade glioma from low grade glioma. This may be useful in deciding the surgical strategy or selecting the site of stereotactic biopsy.
Acknowledgement
This work was supported in part by Grants-in-Aid for Advanced Medical Science Research by the Ministry of Education, Culture, Sports, Science, and Technology, Japan.
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