Rosai-Dorfmann Disease: A Rare Disease Presenting as a Unilateral Neck Swelling.

Rosai-Dorfman disease (RDD) is a rare histiocytic proliferative disorder of unknown etiology. Usually it presents with massive painless cervical lymph node enlargement. Histologically, it shows proliferation of distinctive histiocytic cells that demonstrate emperipolesis in the background of a mixed inflammatory infiltrates. Immunohistochemically, the cells are positive for markers such as CD68 and S100. A 14-year-old boy presented with painless right sided cervical lymphadenopathy without any systemic and other ear, nose, and throat manifestations. The biopsy report of the lymph node showed infiltration of sheets of histiocytes showing emperipolesis with areas of fibrosis and hyalinisation. The sinus histiocytes were strongly positive for S-100 protein. RDD must be considered in the differential diagnosis of massive or multiple lymphadenopathies.