Abstract
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. 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. 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. 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.
Highlights
AND PURPOSE: Atypical and malignant meningiomas are uncommon tumors with aggressive behavior and higher mortality, morbidity, and recurrence compared with benign tumors
The mean apparent diffusion coefficient (ADC) of atypical/ malignant meningiomas (0.66 Ϯ 0.13 ϫ 10Ϫ3 mm2/s) was significantly lower compared with benign meningiomas (0.88 Ϯ 0.08 ϫ 10Ϫ3 mm2/s; P Ͻ .0001)
Meningiomas comprise 14%–20% of all intracranial tumors, with a higher incidence of up to 35.2% among Asians and Africans.[1]. They are generally benign tumors, up to 10% of meningiomas are atypical or malignant, characterized by nuclear disorganization, necrosis, prominent nucleoli, and increased mitoses on histology. Because of their aggressive behavior, atypical/malignant meningiomas are associated with high morbidity and mortality and may invade the adjacent bone and brain parenchyma
Summary
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. Patient Selection We retrospectively reviewed the neuroradiology imaging data base from January 1999 to December 2006 at a tertiary referral neurologic hospital that performs 150 brain tumor surgical procedures per annum.[18] Twenty-five consecutive atypical and malignant meningiomas proved by histologic examination A control group of 23 patients with benign meningiomas was selected from the benign meningothelial meningioma subtype from the same data base. There is evidence that ADC values of meningothelial meningioma may be the lowest among the different subtypes of benign meningiomas[2] and, may represent a suitable homogenous control group for comparison with the low ADC in atypical/malignant tumors. The study was approved by the institutional review board as part of ongoing studies in brain tumors and the neuroradiology data base
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