Diffusion-Weighted MR Imaging: Diagnosing Atypical or Malignant Meningiomas and Detecting Tumor Dedifferentiation

BACKGROUND AND PURPOSE: Atypical and malignant meningiomas are uncommon tumors with aggressive behavior and higher mortality, morbidity, and recurrence compared with benign tumors. We investigated the utility of diffusion-weighted (DW) MR imaging to differentiate atypical/malignant from benign meningiomas and to detect histologic dedifferentiation to higher tumor grade. MATERIALS AND METHODS: We retrospectively compared conventional and DW MR images (b-value 1000 s/mm2) acquired on a 1.5T clinical scanner between 25 atypical/malignant and 23 benign meningiomas. The optimal cutoff for the absolute apparent diffusion coefficient (ADC) and normalized ADC (NADC) ratio to differentiate between the groups was determined by using receiver operating characteristic (ROC) analysis. RESULTS: Irregular tumor margins, peritumoral edema, and adjacent bone destruction occurred sig-nificantly more often in atypical/malignant than in benign meningiomas. The mean ADC of atypical/ malignant meningiomas (0.66 0.13 103 mm2/s) was significantly lower compared with benign meningiomas (0.88 0.08 103 mm2/s; P .0001). Mean NADC ratio in the atypical/malignant group (0.91 0.18) was also significantly lower than the benign group (1.28 0.11; P .0001), without overlap between groups. ROC analysis showed that ADC and NADC thresholds of 0.80 10