What are the characteristic MRI findings of cerebral toxoplasmosis in an immunocompromised patient, and how can it be differentiated from primary CNS lymphoma?

Cerebral toxoplasmosis typically presents with multiple high T2 signal and enhancing mass lesions (1-4 cm) with surrounding vasogenic edema. Larger lesions often show ring enhancement, but unlike bacterial abscesses, they do not exhibit high signal on DWI. Preferred sites include the basal ganglia, white matter, and cortex. The main differential is primary CNS lymphoma, which often presents as a solitary lesion with homogeneous enhancement and restricted diffusion. Clinical pearls include considering the patient's immune status and the presence of systemic symptoms. A common pitfall is mistaking these lesions for metastatic disease in patients with known malignancies.