HIV patient with ring-enhancing brain lesions; most likely etiology?

• A. Cytomegalovirus encephalitis
• B. Toxoplasma gondii encephalitis
• C. Cryptococcus neoformans meningitis
• D. Herpes simplex encephalitis

Answer: (B)

In an HIV patient, multiple ring-enhancing brain lesions most strongly indicate reactivation of Toxoplasma gondii, causing toxoplasmic encephalitis. When CD4 counts are very low, latent Toxoplasma cysts in the brain can reactivate and form focal necrotizing lesions. These lesions often localize to the basal ganglia or the corticomedullary junction and appear as ring-enhancing areas on MRI or CT due to surrounding edema and the inflammatory capsule. Clinically, this pattern fits with subacute neurologic symptoms such as headaches, confusion, and focal deficits.

Other options don’t fit as well because CMV encephalitis typically produces ventriculoencephalitis with periventricular enhancement rather than discrete ring-enhancing lesions; cryptococcal meningitis presents mainly with meningitis signs and meningitis-type imaging features rather than multiple brain lesions; herpes simplex encephalitis classically damages the temporal lobes with hemorrhagic necrosis rather than multiple ring-enhancing lesions.