MRI brain shows a ring-enhancing lesion in the basal ganglia with surrounding oedema in an HIV-positive patient with CD4 count of 50 cells/µL. The MOST likely diagnosis is:

• A Primary CNS lymphoma
• B High-grade glioma (GBM)
• C Bacterial brain abscess
• D Cerebral toxoplasmosis ✓

Explanation

In HIV-positive patients with CD4 <100 cells/µL, multiple ring-enhancing lesions in the basal ganglia/corticomedullary junction with oedema are most likely cerebral toxoplasmosis (Toxoplasma gondii). Thallium-201 SPECT (or FDG PET) showing no uptake in the lesion supports toxoplasmosis over lymphoma (which shows avid uptake). Primary CNS lymphoma (PCNSL) also presents as ring-enhancing mass in HIV but tends to be periventricular and solitary. Empirical anti-toxoplasma treatment is initiated and improvement in 2 weeks confirms the diagnosis.

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.