Difficulties of Differentiating Primary Histiocytic Sarcoma of the Central Nervous System from Glioblastoma in Older Patients: Methylation Analysis and Review of the Literature.

Primary histiocytic sarcoma of the central nervous system is an extremely rare malignancy, with only 43 cases reported to date. It often presents diagnostic challenges due to its rarity and similarities with other central nervous system tumors, particularly glioblastoma. We report a case of primary central nervous system histiocytic sarcoma in a 72-year-old woman, one of the older patients among the reported cases. The patient presented with gait disturbance and left hemiplegia. Initial imaging and intraoperative findings suggested a high-grade glioma. However, comprehensive pathological examination, including immunohistochemistry, electron microscopy, and genetic analyses, led to the diagnosis of histiocytic sarcoma. Notably, the tumor exhibited CDKN2A homozygous deletion and a unique methylation profile distinct from gliomas. Despite treatment with surgery, radiation, and chemotherapy, the patient experienced meningeal dissemination 8 months post-surgery and died 11 months after diagnosis. This case highlights the importance of comprehensive diagnostic evaluation in challenging central nervous system tumors and provides valuable insights into the molecular characteristics of central nervous system histiocytic sarcoma, particularly regarding CDKN2A deletion and methylation patterns. Awareness of this rare entity is crucial for accurate diagnosis and appropriate management of central nervous system tumors.