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 ).
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
uniform contrast enhancement is essentially diagnostic.
May have a dural tail.
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 )
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.