Cerebral CD1a positive Rosai–Dorfman disease with coexistent granulomatous angiitis: A case report

Rosai–Dorfman disease (RDD) is a nonneoplastic histiocytic proliferation. RDD is CD1a negative as opposed to Langerhans cell histiocytosis (LCH). The lesion was positive for CD1a immunohistochemistry in our RDD patient, suggesting an overlap with LCH. In addition, our case exhibited granulomatous angiitis (GA) on microscopy. We report the first triad of coexistent intracranial RDD-LCH-GA. A 30-year-old man presented with seizures, limb weakness, and violent behavior for 3 months. There was no fever, lymphadenopathy, or hepatosplenomegaly. Laboratory test results were normal. Radioimaging revealed an 8.6 cm × 7.4 cm × 3.2 cm mass in the parietotemporal lobe. It was hypointense on T1W1 and hypointense on T2W1, suggestive of glioma or tumefactive demyelination. A subtotal resection was performed. Histopathology exhibited mature lymphocytes, plasma cells, and histiocytes with emperipolesis. Vessels showed transmural granulomatous inflammation. Fungal and mycobacterial stains were negative. Immunohistochemistry revealed positivity for CD68, S100, and CD1a. The patient refused to undergo postoperative adjuvant radiotherapy. He remained asymptomatic for 6 months but was lost to follow-up thereafter. RDD-LCH concurrence may represent a clonal transformation in a common precursor histiocyte. Coexistent GA requires resection followed by steroid or cyclophosphamide therapy to prevent disease progression.