Central China Rosai-Dorfman Disease Registry

Inclusion Criteria: Diagnosis of a histiocytic disorder as determined by a corroborating constellation of histopathology, clinical, and/or radiologic findings. All participants will undergo Standard of Care MRA, CTA or imaging examination. Exclusion Criteria: Known intracranial involvement of histiocytosis (including dura, leptomeninges and brain parenchyma) Prior stroke or intracranial hemorrhage Other (non-histiocytic) intracranial neoplasm or neurological disorder deemed by the PI or Co-PI to confound neuroimaging studies (e.g., demyelinating disease) Existing diagnosis of a psychiatric disorder or untreated mood disturbance Existing diagnosis of a neurodegenerative disease, such as Alzheimer'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 months or longer at any time in the past History of severe claustrophobia or other contraindications to patient SOC brain MRI Prior intravenous cytarabine or cladribine Other current or prior treatments (e.g., high-dose chemotherapy for a different cancer) deemed by the PI or Co-PI to confound imaging studies or cognitive performance