Figure 3.

A focal brain lesion in an AIDS patient (toxoplasmosis versus lymphoma). An axial T1 image after intravenous gadolinium administration (A) shows a large periventricular lesion in the left thalamus with extensive necrosis (asterisk) and thick peripheral enhancement. An axial apparent diffusion coefficient map (B) confirmed a very low signal intensity in the solid portion of the lesion (arrowheads) compared with the central area of necrosis (asterisk). Additionally, note the hyperintensity of the perilesional vasogenic edema. Proton magnetic resonance spectroscopy (C) confirmed the presence of elevated lipid and lactate (0.9–1.3 ppm) and choline levels with reduced N-acetylaspartate levels. A magnetic resonance perfusion sequence (dynamic susceptibility contrast magnetic resonance image T2*) (D) confirmed the absence of neoangiogenesis (low relative cerebral blood volume). These features supported the diagnosis of lymphoma.