4. Clues to diagnosis: Astrocytoma <ul><li>Heterogenous mass </li></ul><ul><li>often infiltrate into adjacent brain </li></ul><ul><li>rarely have the clear margins </li></ul>
6. Clues to diagnosis: Oligodendroglioma <ul><li>Evidence of calcification in 30% of cases. </li></ul>
7. CNS lymphoma Proton density–weighted MR image through the temporal lobe demonstrates a low signal intensity nodule ( small arrows ) surrounded by a ring of high signal intensity edema ( larger arrows ).
8. T1-weighted contrast-enhanced axial MRI demonstrates ring enhancement surrounded by a nonenhanced rim of edema. In this patient with AIDS, a solitary lesion of this type is consistent with either lymphoma or toxoplasmosis; the presence of multiple lesions favors toxoplasmosis
10. Clues to diagnosis: Meningioma <ul><li>Does not usually invade the brain </li></ul><ul><li>uniform contrast enhancement is essentially diagnostic. </li></ul><ul><li>May have a dural tail. </li></ul>
11. Schwannomas Axial noncontrast MR scan through the cerebellopontine angle demonstrates an extraaxial mass that extends into a widened internal auditory canal, displacing the pons ( arrows )
12. Schwannoma Postcontrast T1-weighted image demonstrates intense enhancement of the vestibular schwannoma ( white arrow ). Abnormal enhancement of the left fifth nerve ( black arrow ) most likely represents another schwannoma in this patient with neurofibromatosis type 2.