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Diffusion-weighted MR imaging: diagnosing atypical or malignant meningiomas and detecting tumor dedifferentiation
1Department of Neuroradiology, National Neuroscience Institute, Singapore.
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/mm(2)) 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 significantly more often in atypical/malignant than in benign meningiomas. The mean ADC of atypical/malignant meningiomas (0.66 +/- 0.13 x 10(-3) mm(2)/s) was significantly lower compared with benign meningiomas (0.88 +/- 0.08 x 10(-3) mm(2)/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 x 10(-3) mm(2)/s and 0.99, respectively, had the best accuracy: at the NADC threshold of 0.99, the sensitivity and specificity were 96% and 100%, respectively. Two patients had isointense benign tumors on initial DW MR imaging, and these became hyperintense with the decrease in ADC and NADC below these thresholds when they progressed to atypical and malignant meningiomas on recurrence.
Conclusions:
ADC and NADC ratios in atypical/malignant meningiomas are significantly lower than in benign tumors. Decrease in ADC and NADC on follow-up imaging may suggest dedifferentiation to higher tumor grade.
Insights
Diffusion-weighted MRI can differentiate aggressive meningiomas from benign ones. Lower apparent diffusion coefficient (ADC) and normalized ADC (NADC) values indicate higher-grade tumors and potential dedifferentiation.
Area of Science:
- Radiology
- Oncology
- Neuroscience
Background:
- Atypical and malignant meningiomas exhibit aggressive behavior, leading to higher mortality and recurrence rates compared to benign types.
- Distinguishing between tumor grades is crucial for effective treatment planning and prognosis.
Purpose of the Study:
- To evaluate the effectiveness of diffusion-weighted (DW) Magnetic Resonance (MR) imaging in differentiating atypical/malignant meningiomas from benign meningiomas.
- To assess the capability of DW MR imaging in detecting histologic dedifferentiation to higher tumor grades.
Main Methods:
- A retrospective analysis compared conventional and DW MR images (b-value 1000 s/mm(2)) of 25 atypical/malignant and 23 benign meningiomas.
- Receiver operating characteristic (ROC) analysis determined optimal cutoff values for absolute apparent diffusion coefficient (ADC) and normalized ADC (NADC) ratios.
Main Results:
- Atypical/malignant meningiomas showed significantly lower mean ADC (0.66 ± 0.13 x 10(-3) mm(2)/s) and NADC ratios (0.91 ± 0.18) compared to benign meningiomas (ADC: 0.88 ± 0.08 x 10(-3) mm(2)/s; NADC: 1.28 ± 0.11).
- ROC analysis identified ADC and NADC thresholds of 0.80 x 10(-3) mm(2)/s and 0.99, respectively, with 96% sensitivity and 100% specificity for NADC at its threshold.
- Two benign tumors that progressed to higher grades showed decreased ADC and NADC values on follow-up imaging.
Conclusions:
- Significantly lower ADC and NADC ratios are characteristic of atypical/malignant meningiomas compared to benign tumors.
- A decrease in ADC and NADC values during follow-up imaging may indicate dedifferentiation to a higher tumor grade.
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