Intracranial Rosai–Dorfman Disease Presenting as a Posterior Fossa Dural-Based Mass Mimicking Meningioma: A Case Report

Background and Clinical Significance: Rosai–Dorfman disease (RDD) is a rare non-Langerhans-cell histiocytosis that infrequently involves the central nervous system. Intracranial RDD commonly presents as a dural-based enhancing mass that radiologically resembles a meningioma. Posterior fossa involvement is particularly uncommon and may cause cerebellar compression and obstructive hydrocephalus. Case Presentation: A 58-year-old man with biopsy-confirmed systemic extranodal RDD presented with progressive headache, nausea, severe dizziness, gait instability, cerebellar ataxia, and right upper-limb dysmetria despite corticosteroid therapy. Brain magnetic resonance imaging demonstrated a strongly enhancing right posterior fossa dural-based mass with vasogenic edema, cerebellar compression, fourth-ventricular effacement, and mild obstructive hydrocephalus. A smaller anterior dural-based enhancing lesion was also identified. The radiological differential diagnosis included meningioma, metastatic disease, and an inflammatory lesion. Following multidisciplinary perioperative management of anemia and complex transfusion incompatibility, gross-total resection of the symptomatic posterior fossa lesion was achieved. Histopathological examination demonstrated histiocytic proliferation with emperipolesis. The lesional histiocytes expressed S100 and CD68, showed nuclear Cyclin D1 expression in approximately 30% of lesional histiocytes, and were negative for CD1a, supporting the diagnosis of intracranial extranodal RDD. Postoperatively, the patient’s headache and cerebellar manifestations improved. Follow-up imaging demonstrated complete resection of the posterior fossa lesion, resolution of the mass effect and hydrocephalus, and no recurrence at the resection site. Extracranial disease subsequently progressed, emphasizing the distinction between local and systemic disease control. Conclusions: Intracranial RDD should be considered in the differential diagnosis of meningioma-like posterior fossa masses, particularly in patients with systemic RDD. Histopathological and immunohistochemical confirmation is essential. Timely surgical resection can provide a definitive diagnosis, effective decompression, and sustained neurological improvement, while continued systemic surveillance remains necessary.