A 40-year-old HIV-positive man with CD4 count below 100 cells/microliter develops progressive confusion and left hemiparesis over three weeks. MRI shows a solitary homogeneously enhancing periventricular mass with mild edema. Stereotactic biopsy reveals large atypical lymphoid cells angiocentrically distributed around necrotic vessels, positive for CD20 and EBV-encoded RNA by ISH. What is the diagnosis?
- A Primary central nervous system lymphoma ✓
- B Cerebral toxoplasmosis
- C Metastatic high-grade B-cell lymphoma
- D Glioblastoma, IDH-wildtype
Explanation
In severely immunosuppressed patients, primary CNS lymphoma is almost always diffuse large B-cell type, EBV-associated, and presents as a solitary periventricular enhancing mass. The biopsy hallmark is malignant lymphocytes accumulating around blood vessel walls (angiocentricity) with associated necrosis. Toxoplasma produces multiple peripheral ring-enhancing lesions with marked edema and responds to anti-Toxoplasma therapy. Systemic lymphoma metastasizing to brain parenchyma is rare. Glioblastoma shows GFAP-positive astrocytic differentiation, not CD20 positivity.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.