Central nervous system Burkitt lymphoma: fornix-to-ventricle dissemination.

Central nervous system Burkitt lymphoma (BL) is exceptionally rare in adolescents without systemic disease. We report a 16-year-old female presenting with progressive headaches and isolated fornix lesions on MRI. Following an initial presumptive diagnosis of viral encephalitis, empiric administration of low-dose dexamethasone and antivirals induced transient symptomatic improvement. A follow-up MRI 50 days later revealed a fulminant "spark-to-wildfire" imaging progression, characterized by multifocal ventricular dissemination and obstructive hydrocephalus. Histopathology and fluorescence in situ hybridization (FISH) confirmed the BL diagnosis. This case highlights the extreme biological aggressiveness of central nervous system BL and the diagnostic challenges of atypical fornix involvement, underscoring the necessity of serial neuroimaging assessment and prompt pathological biopsy for accurate diagnosis.