A 45-year-old HIV-positive patient develops hemiparesis. MRI shows a solitary ring-enhancing lesion in the basal ganglia with surrounding edema. Thallium-201 SPECT shows a 'hot spot' in the lesion. The most likely diagnosis is:
- A Cerebral toxoplasmosis
- B CNS lymphoma ✓
- C Tuberculoma
- D Brain abscess (bacterial)
Correct answer: B. CNS lymphoma
Explanation
Primary CNS lymphoma in HIV patients shows avid uptake on Thallium-201 SPECT ('hot spot') because it is a metabolically active tumor. Cerebral toxoplasmosis, the most common cause of ring-enhancing lesions in HIV, shows absent or low Tl-201 uptake ('cold spot') because it is an infectious lesion rather than tumor. This nuclear medicine distinction — hot (lymphoma) vs. cold (toxoplasmosis) — is a classic teaching point. Tuberculoma and bacterial abscess also show cold spots.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.