Intraoperative Frozen Section Diagnosis of Brain Rosai-Dorfman Disease Clinically and Radiologically Mimicking Meningioma.

BACKGROUND/AIM: Rosai-Dorfman disease (RDD), also known as sinus histiocytosis with massive lymphadenopathy, is a rare, benign, histiocytic proliferative disorder characterized by nonpainful lymphadenopathy. Nonmalignant histiocytes can also infiltrate extranodal sites such as in the skin and central nervous system. On imaging, RDD can mimic other disorders such as meningioma, which is more common, and requires histology and immunohistochemistry to elucidate diagnosis.

CASE REPORT: Herein we report a case of a 20-year-old female who presented to the emergency department (ED) after near-syncope episode following methamphetamine and opioid use. Initial computed tomography (CT) found a 2.3 cm mass in the right frontoparietal region. Further examinations with magnetic resonance imaging (MRI) revealed findings compatible with meningioma. After one month of persistent symptoms, the "meningioma" was resected and the intraoperative frozen sections (FS) and touch preparation cytopathology of the mass showed mixed inflammatory infiltrates and scattered large, atypical appearing cells that display emperipolesis, raising suspicions of an RDD diagnosis instead of meningioma. The permanent sections confirmed the histological findings on FS. The large atypical lesional histiocytes showing emperipolesis with engulfment of lymphocytes, plasma cells and neutrophils. The lesional cells were immunoreactive for protein S100, cluster of differentiation 163 (CD163), and B cell lymphoma 1 (BCL-1), negative for CD1a. Based on histology and immunohistochemical profile, the final diagnosis was Rosai-Dorfman Disease. Postoperatively, there was immediate improvement in patient's strength and symptoms. At the 9-month follow up post-surgery, she was doing well, and MRI revealed no evidence of residual or recurrent disease.

CONCLUSION: This case is a rare example of RDD clinically and radiologically mimicking meningioma and illustrates the importance of rigorous histological analysis for accurate diagnosis, particularly during the intraoperative consultation, to ensure proper treatment.