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Rosai–Dorfman disease (RDD) is a rare non-Langerhans cell histiocytosis characterized by painless cervical lymphadenopathy but may rarely involve the central nervous system (CNS). Isolated intraventricular involvement is exceptionally rare and may clinically and radiographically mimic primary brain tumors or inflammatory pseudotumor syndromes encountered in autoimmune neurology practice.

[Case Presentation]

A 19-year-old male without significant medical history developed progressive holocranial headache with nausea and vomiting over 10 months, though neurologic examination revealed no focal deficits. Advanced neuroimaging identified a well-circumscribed intraventricular mass occupying the temporal and occipital horns of the left lateral ventricle measuring 5 × 4 × 5.1 cm with perilesional edema, sulcal effacement, ipsilateral ventricular compression, and 10 mm rightward midline shift, accompanied by a separate extraconal orbital lesion. 

Following left temporoparietal craniotomy with complete surgical resection, histopathologic analysis revealed characteristic sheets of histiocytes exhibiting abundant vacuolated cytoplasm, vesicular nuclei, focal emperipolesis, and admixed lymphoplasmacytic infiltrate with Touton-type giant cells. Immunohistochemical profiling demonstrated CD68+, CD163+, factor XIIIa+, patchy S100 positivity, and CD1a negativity, with absence of BRAF V600E mutation and low IgG4:IgG ratio, establishing the diagnosis of Rosai–Dorfman disease and excluding juvenile xanthogranuloma.

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Primary intraventricular RDD represents an uncommon manifestation and may closely mimic neoplastic or autoimmune inflammatory CNS lesions. Recognition of characteristic histopathologic and immunophenotypic features is essential for accurate diagnosis. The present case underscores the critical importance of including intraventricular Rosai-Dorfman disease in the differential diagnosis when evaluating young patients with chronic progressive headache and imaging findings of intraventricular mass lesions with associated mass effect.