The Value Of Multimodality MR Imaging In The Differential Diagnosis Of WHO Grade Ⅱ And Grade Ⅲ Pleomorphic Xanthoastrocytoma

Background and purpose:According to the latest world health organization of central nervous system of tumors,anaplastic pleomorphic xanthoastrocytoma（APXA）,as a distinct type of astrocytoma that defined as≥5 mitoses per 10 high power fields,may exhibited aggressive clinical behavior and relatively worse prognosis compared with pleomorphic xanthoastrocytoma（PXA）.The purpose of this study was to investigate the imaging characteristics of multimodality magnetic resonance imaging（MRI）of these two entities and evaluate the clinical value of multimodality MRI in distinguishing APXA from PXA.Materials and methods:The retrospective study included 11 patients with PXA and 10patients with APXA from December 2007 to December 2017,who confirmed by surgery and pathology in our hospital,underwent conventional and advanced MR imaging before surgical operation.Conventional MR imaging was performed in all patients,DWI in 10 patients with PXA and 9 patients with APXA,DSC-PWI in 4patients with PXA and 5 patients with APXA.The conventional imaging features,including tumor location,size,cystic degeneration,enhancement pattern,and peritumoral edema was analyzed.The parameters of minimum apparent diffusion coefficients(rADC_min)ratio and relative maximum cerebral blood volume(rCBV_max)ratio were obtained from regions of the contrast-enhanced potions of tumors and contralateral thalamus respectively.The Mann-Whitney U test was used to assess the differences for tumor diameter,peritumoral edema,rADC_min ratio and rCBV_maxax ratio between APXA and PXA.In addition,the Chi-Square test was used to assess the differences for the age,sex,tumor location,cystic degeneration and enhancement characteristics of solid components.P values less than 0.05 were considered to indicate statistical significance.Receiver operating characteristic curve（ROC）was performed to determine the best diagnostic threshold of rADC_min ratio and rCBV_maxax ratio for differentiating APXA from PXA respectively,and the corresponding sensitivity,specificity,accuracy,positive predictive value,negative predictive value was calculated.Results:（1）Tumor diameter of APXA was larger than that of PXA（4.68±0.53cm vs3.15±1.05cm,P=0.002）.Heterogeneous enhancement was seen in 90%of the APXA cases,while only seen in 27.2%of the PXA cases.There were significant differences in enhancement pattern between PXA and APXA groups（P=0.004）.The extent of peritumoral edema in APXA group was also larger than PXA group（2.34±0.90cm vs1.00±0.96cm,P=0.007）.In addition,there were no significant differences in age,gender,tumor location,and cystic degeneration between these two group,respectively（P>0.05）.（2）The rCBVmax ratio in APXA group was significantly higher than that in PXA group（2.64±0.78 vs 1.69±0.35,P=0.027）,while the rADC_min ratio in APXA group was significantly lower than that in PXA group（0.98±0.16 vs 1.46±0.44,P=0.001）（2）The maximum Youden index was chosen to identify the best diagnostic thresholds of varieties of interests in ROC analysis.The area under the curve（AUC）of rADC_min ratio and rCBVmax ratio was 0.944 and 0.950,respectively.The optimum thresholds value of1.02 for rADC_min ratio in differentiating PXA from APXA provided sensitivity,specificity,accuracy,positive predictive values,and negative predictive values of77.78%,90.00%,84.21%,87.5%,and 81.82%,respectively.The optimum thresholds value of 2.2 for rCBV_max ratio provided sensitivity,specificity,accuracy,positive predictive values,and negative predictive values of 80.00%,100.00%,100.00%,80.00%,and 88.89%,respectively.Conclusion:Compared with PXA,APXA showed the imaging features of greater tumor size,heterogeneous contrast enhancement,obvious peritumoral edema,lower rADC_minin ratio and higher rCBV_max ratio.The multimodality MRI techniques,which combined conventional MR scan,DWI and DSC-PWI are helpful in the characterization and differentiation of PXA and APXA.