Diagnostic value of proton magnetic resonance spectroscopy in the noninvasive grading of solid gliomas: comparison of maximum and mean choline values.

OBJECTIVE

Magnetic resonance spectroscopy is widely used in addition to magnetic resonance imaging in the characterization of brain tumors. Compounds containing choline (Cho) have an important role in the evaluation of tumor malignancy. For this purpose, various ratios of Cho and other metabolites, such as creatine (Cr), have been assessed. The aim of this study was to compare normalized mean and maximum levels of Cho as single parameters in the noninvasive grading of gliomas.

METHODS

Proton spectroscopic imaging data of 63 patients with suspected World Health Organization (WHO) grade II or III gliomas were acquired at 3 T. Cho concentrations of the tumor were analyzed by a frequency domain fit and normalized to the corresponding contralateral healthy brain tissue. Metabolite images were used to determine the maximum and mean Cho as well as Cr concentrations of the tumor. Furthermore, contrast enhancement of the tumor was analyzed on standard magnetic resonance imaging. All patients subsequently underwent tumor resection or stereotactic biopsy to confirm diagnosis of glioma. Statistical analysis using the Kruskal-Wallis test, Mann-Whitney U test, and receiver operating characteristic curve analysis was performed with BiAS software (Epsilon Verlag GmbH, Frankfurt, Germany).

RESULTS

Histopathological examinations revealed WHO grades II (n = 27), III (n = 26), and IV (n = 10). There was a statistically significant difference in both normalized maximum and mean Cho between WHO grade II and non-necrotic WHO grade III/IV gliomas (mean, 1.45 +/- 0.28 versus 2.16 +/- 0.36, P < 0.05; maximum, 1.64 +/- 0.32 versus 3.32 +/- 0.55, P < 0.0001). Receiver operating characteristic analyses rendered a 2.02 cutoff value for maximum Cho with a sensitivity and specificity of 86.1% and 77.8%, respectively. For mean Cho, we found a cutoff value of 1.52 (sensitivity, 77.8%; specificity, 63.0%). The diagnostic accuracy of maximum Cho was superior to that of mean Cho and also the ratio of Cho/Cr (82.5% versus 71.4% and 72.1%, respectively), but all 3 parameters were superior to contrast enhancement of the tumor (61.9%).

CONCLUSION

Both maximum and mean Cho differ between low- and high-grade gliomas. Compared with contrast enhancement, mean Cho, and Cho/Cr, maximum Cho of the tumor provides the highest accuracy in discriminating between low- and high-grade tumors, indicating usefulness of this single parameter in the process of therapeutic decision making.