The "Eccentric Target Sign" in Cerebral Toxoplasmosis: A Diagnostic Clue in an HIV-Positive Patient

Background: Among the opportunistic infections affecting the central nervous system in AIDS patients, cerebral toxoplasmosis remains a primary diagnostic concern, especially when CD4 counts drop below the 100 cells/mm³ threshold. Case Presentation: We describe the clinical course of a 22-year-old HIV-positive male who presented with a sudden onset of consciousness disorders. Brain MRI at 1.5 Tesla identified multifocal nodular lesions involving the basal ganglia, thalami, and corticomedullary junctions. Results: The lesions exhibited a specific "concentric target sign" on T2/FLAIR sequences. Post-contrast imaging was even more revealing, showing the pathognomonic "eccentric target sign"—a small enhancing nodule located along the internal wall of a ring-enhancing abscess. Diffusion-weighted imaging (DWI) showed only discrete ADC restriction, a key finding to rule out the intense restriction typically seen in CNS lymphoma. Thalamic hemorrhagic stigmata were also identified. Conclusion: In the setting of severe immunosuppression, these specific MRI signatures provide enough diagnostic certainty to initiate an empirical therapeutic trial. This approach effectively bypasses the need for high-risk brain biopsies and significantly reduces neurological morbidity.