Figure 12b. Oligoastrocytoma. (a) Axial T1-weighted MR image shows a hypointense mass (arrow) in the right frontal lobe. (b) Axial T2-weighted MR image shows heterogeneity of the mass with exophytic extension. (c) Axial diffusion-weighted MR image shows that the mass is predominantly isointense relative to the adjacent gray matter. (d) Axial contrast-enhanced T1-weighted MR image shows no enhancement of the mass.