Response

Abstract

We greatly appreciate the comments on the article “Diagnostic value of minimum apparent diffusion coefficient values in prediction of neuroepithelial tumor grading” (1) by Professor Viroj Wiwanitkit. Their main concern was about the diagnostic accuracy, false positive and false negative of minimum apparent diffusion coefficient (MinADC) values in tumor grading. As shown in Table 3 and Figure 4 in the article, the area under the ROC curve (AUC) for G2 (WHO II) versus G3 (WHO III) (0.78 ± 0.06) suggested a fair level for discrimination between G2 and G3, and AUC for G3 (WHO III) versus G4 (WHO IV) (0.51 ± 0.10) demonstrated a failure level for discrimination between G3 and G4. But both AUC for low-grade glioma (LGG) versus high-grade glioma (HGG) (0.81 ± 0.04) and AUC for G2 (WHO II) versus G4 (WHO IV) (0.82 ± 0.04) indicated good levels. The ROC analysis demonstrated that the MinADC value could be used for tumor grading, especially between LGG and HGG, but there were some limits for G2 versus G3, and G3 versus G4. As a diagnostic tool of tumor grading between LGG and HGG, MinADC value can provide more diagnostic information although overlap (including false positive and false negative) exists. Therefore, one should be cautious when using MinADC as a single tumor grading tool, and confidence in tumor grading could be improved by combing other MR techniques such as contrast-enhanced MRI, MR spectroscopy (2), and perfusion weighted imaging (3), especially for the nonenhancing brain tumor with a low MinADC (4). In clinical practice, we have used the cutoff value for discrimination between LGG and HGG and acquired satisfactory results. The article “Quantitative apparent diffusion coefficients in the characterization of brain tumors and associated peritumoral edema” (5) mainly used ADC value to differentiate the infiltrated edema in high-grade glioma from vasogenic edema in metastases, while our article mainly referred to the differentiation of neuroepithelial tumor grading (mainly for LGG versus HGG). In our article, we did discuss the MinADC values of several subtypes of neuroepithelial tumors, including astrocytic tumors, oligodendroglial tumors, oligoastrocytic tumors, and ependymal tumors. In conclusion, we believe that MinADC value may be a simple and effective optional tool for the prediction of neuroepithelial tumor grading. Zhiye Chen MD*, Xin Lou MD, PhD*, Lin Ma MD, PhD*, * Department of Radiology, PLA General Hospital, Beijing, China.