Rosai-Dorfman Disease of pancreas: rare aetiology mimicking malignancy.

Rosai-Dorfman disease (RDD) is a non-Langerhans cell histiocytosis which usually presents as painless lymphadenopathy. Extranodal involvement is known to occur in various organs, and less than ten cases with primary pancreatic involvement have been reported previously. This case report details the clinical course of an elderly female, presenting with upper abdominal discomfort and imaging suggestive of malignancy. Multiple non-diagnostic fine-needle aspirations were followed by surgical intervention. Histopathological evaluation revealed a pancreatic mass with characteristic features of RDD. The large hallmark RDD histiocytes showed pale, watery-clear cytoplasm, central round nucleus, and prominent nucleolus, with and without lymphocyte emperipolesis. The RDD histiocytes showed positive immunostaining for CD68, CD163, S100 (nuclear and cytoplasmic), OCT-2, Cyclin D1 and are negative for CD1a, Factor XIIIa, fascin and langerin. This case underscores the importance of considering RDD in the differential diagnosis of pancreatic masses alongwith comprehensive evaluation, multidisciplinary approach and pancreatic core needle biopsy evaluation.