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.