Central China Rosai-Dorfman Disease Registry

Inclusion Criteria: Diagnosis of a histiocytic disorder as determined by a corroborating constellation ofhistopathology, clinical, and/or radiologic findings. All participants will undergoStandard of Care MRA, CTA or imaging examination.

Exclusion Criteria: Known intracranial involvement of histiocytosis (including dura, leptomeninges and brainparenchyma) Prior stroke or intracranial hemorrhage Other (non-histiocytic) intracranialneoplasm or neurological disorder deemed by the PI or Co-PI to confound neuroimagingstudies (e.g., demyelinating disease) Existing diagnosis of a psychiatric disorder oruntreated mood disturbance Existing diagnosis of a neurodegenerative disease, such asAlzheimer's disease Chronic or daily excessive alcohol consumption as determined by the PI.History of chronic use of corticosteroids, defined as continuous treatment for six monthsor longer at any time in the past History of severe claustrophobia or othercontraindications to patient SOC brain MRI Prior intravenous cytarabine or cladribine Othercurrent or prior treatments (e.g., high-dose chemotherapy for a different cancer) deemed bythe PI or Co-PI to confound imaging studies or cognitive performance