Cell-dense tumors may restrict diffusivity which can be measured by diffusion-weighted MRI (DWI), and which is quantified by the apparent diffusion coefficient (ADC). Little is known about diffusivity in meningiomas. These tumors frequently show hemorrhage and calcification which can be demonstrated using susceptibility weighted MRI (SWI). Both DWI and SWI represent T2-derived MRI sequences. Here we investigated ADC variability in meningiomas and analyzed whether susceptibility changes (SWI_pos) alter diffusivity.

We grouped newly diagnosed meningiomas according to the presence (SWI_pos) or absence (SWI_neg) of susceptibility changes. ADC values were calculated using region-of-interest analysis, and ADC values of SWI_pos and SWI_neg meningiomas were compared. In addition ADC histograms were created.

We retrospectively studied 36 patients (13 WHO grade I, 8 WHO grade II, 15 suspected meningiomas). Thirteen meningiomas (36%) exhibited SWI_pos. Global ADC values were higher in SWIpos (1.00±0.15×10–3mm²/s) compared to SWI_neg (0.82±0.09×10–3mm²/s) tumors (P<0.0001). Meningiomas showing both SWI_pos and SWI_neg areas caused two separated histogram peaks, whereas homogeneously appearing meningiomas with either SWI_posor SWI_neg areas showed one peak only. ADC values did not correlate with age or gender, and showed substantial overlap between WHO grade I and II.

Susceptibility changes (SWI_pos) in meningiomas influence measures of diffusivity by increasing ADC values on average by 38%. This shift has to be considered when conclusions on tumor behavior are drawn from DWI. Further studies should address whether ADC changes and histogram patterns can be used to monitor treatment of meningiomas.