MRI - AIDS, toxoplasmosis: This 50-year-old man with AIDS (CD4+ = 45/(L) presented with weakness and difficulty walking. Examination was significant for truncal instability and bilateral hyperreflexia. The T1-weighted axial MR image on the left shows a predominantly low-signal rounded mass within the pons with mass effect and slight effacement of the fourth ventricle. The post-contrast magnetization transfer image on the right shows peripheral enhancement of the mass.