A Challenging Rare Case: Rosai-Dorfman Disease Presented as a Single Osseus Lesion in a 16-Month-Old Boy

Sinus histiocytosis with massive lymphadenopathy (also known as Rosai-Dorfman disease (RDD)), a rare non-Langerhans cell histiocytosis, was originally recognized in 1969 by Rosai and Dorfman. RDD is characterized by the accumulation of activated histiocytes in various tissues and organs, but most commonly in lymph nodes. RDD is subclassified in two forms. The more common form, nodal RDD, and the rare form, extranodal RDD, which is based on the presence of extranodal tissue involvement. Most extranodal RDDs also involve lymph nodes. Primary, exclusively extranodal RDD is rare, and is exceedingly uncommon in young pediatric patients. These cases have rarely been reported in the current medical literature. In this case report, we present the diagnostic work-up of an osseous RDD in a 16-month-old male.