Pediatric hemophagocytic lymphohistiocytosis with predominant CNS involvement: MRI features and differential diagnosis

BACKGROUND: Hemophagocytic lymphohistiocytosis (HLH) is a rare, life-threatening hyperinflammatory disorder resulting from immune dysregulation that leads to uncontrolled macrophage activation. The diagnosis of HLH is often challenging, as its clinical manifestations can mimic various systemic conditions, including sepsis, autoimmune disorders, and malignancies. This overlap, combined with the rapid progression of the disease, may delay treatment and increase morbidity and mortality. Neurological involvement is particularly frequent in pediatric cases. Neuroimaging plays a critical role in raising suspicion for HLH, especially when classical clinical criteria are incomplete. CASE PRESENTATION: We report a 3-year-old male patient who presented with growth retardation and long-standing polyuria and polydipsia, followed by acute respiratory distress requiring intensive care admission. During hospitalization, neurological deterioration prompted cranial magnetic resonance imaging (MRI). Imaging revealed diffuse infiltrative lesions involving the cerebral cortex, deep gray matter, white matter, brainstem, corpus callosum, and optic chiasm, with marked perivascular and leptomeningeal contrast enhancement, microhemorrhages, and cerebral venous thrombosis. Due to progressive neurological involvement and atypical imaging findings, a brain biopsy was performed, demonstrating histiocytic infiltration and hemophagocytosis. According to the HLH-2004 diagnostic criteria, the overall clinical, laboratory, and histopathological findings were consistent with hemophagocytic lymphohistiocytosis (HLH). Treatment was initiated according to the HLH-2004 protocol; however, the disease followed an aggressive course with a fatal outcome. CONCLUSION: This case highlights the diagnostic value of neuroimaging in pediatric HLH with predominant CNS involvement and underscores the importance of considering HLH in the differential diagnosis of diffuse infiltrative brain lesions. Brain MRI findings, particularly when correlated with histopathology, can play a crucial role in establishing the diagnosis and guiding timely management.