Primary Intramedullary Histiocytic Sarcoma with Leptomeningeal Dissemination: Imaging, Pathologic, and Molecular Correlation.

Central nervous system histiocytic sarcoma is exceedingly uncommon, particularly with intramedullary spinal cord involvement. We describe a 27-year-old man presenting with motor weakness and radiating pain. MRI revealed a homogeneously enhancing intramedullary mass at the C2-3 level with diffuse leptomeningeal dissemination, raising suspicion for a disseminated neoplastic process. Histopathology demonstrated pleomorphic large histiocyte-like cells with strong CD163, CD68, and lysozyme expression, confirming histiocytic sarcoma. Targeted next-generation sequencing detected a TP53 hotspot mutation (p.Arg273His), classified as a Tier II variant according to the joint AMP/ASCO/CAP guidelines, while additional variants were of uncertain clinical significance. This case highlights the rare intramedullary presentation of histiocytic sarcoma with leptomeningeal dissemination and emphasizes the importance of radiologic-pathologic correlation for accurate diagnosis.