Diagnostic accuracy of diffusion weighted imaging for differentiation of supratentorial pilocytic astrocytoma and pleomorphic xanthoastrocytoma

Supratentorial pilocytic astrocytoma (PA) may mimic pleomorphic xanthoastrocytoma (PXA) on conventional MR imaging, and a differentiation is clinically important because of distinct recurrence rate and anaplastic transformation rate. The purpose of this study was to investigate the diagnostic potential of diffusion-weighted imaging (DWI) in differentiating supratentorial PA from PXA. We retrospectively reviewed DWI and conventional MR imaging of 16 patients with supratentorial PA and 8 patients with PXA. Variables of mean ADC values (ADC(mean)) and minimum ADC values (ADC(min)) were calculated from the ROIs containing the contrast-enhancing lesion on DWI. ADC(mean) values and ADC(min) values were compared among all supratentorial PA and PXA as well as between the subgroup of lobar PA and PXA by using an unpaired Student's t test. The optimum threshold, sensitivity, specificity, accuracy, and the area under the receiver operating characteristic curve (AUC) were determined. Both ADC(mean) values (1542 +/- 186 vs 1084 +/- 201 x 10(-6) mm(2)/s; P < 0.001) and ADC(min) values (1355 +/- 183 vs 988 +/- 180 x 10(-6) mm(2)/s; P < 0.001) were significantly higher in supratentorial PA compared with PXA. The ADC(mean) values and ADC(min) values were also significantly higher in lobar PA than those in PXA. The ADC(mean) values were useful for differentiating supratentorial PA from PXA, with a threshold value of > 1189.8 x 10(-6) mm(2)/s (sensitivity, 93.8%; specificity, 100%). The optimal threshold values of > 1189.8 x 10(-6) mm(2)/s for ADC(mean) values provide sensitivity and specificity of 85.7 and 100%, respectively, for discriminating lobar PA from PXA. The optimum threshold value for ADC(min) was > 1063.5 x 10(-6) mm(2)/s. DWI is helpful in characterization and differentiation of supratentorial PA from PXA.