Extranodal soft tissue Rosai-Dorfman disease of the head and neck and its diagnostic difficulty.

Rosai-Dorfman disease (RDD) is a rare proliferative histiocytic disorder that is characterized by persistent massive lymphadenopathy mimicking malignant tumors. Extranodal RDD is uncommon, and more severe fibrosis and fewer histiocytes in lesions make the diagnosis of RDD more difficult than that of nodal RDD. We herein described a 31-year-old male patient with isolated soft tissue RDD of the head and neck. The patient was referred to our hospital with a right neck mass. Computed tomography (CT) scans showed a diffuse enhanced tumor with an unclear border in the right side of the neck. 18F-fluorodeoxyglucose positron emission tomography (PET)/CT revealed high uptake in the corresponding lesion. Second wide local excisional biopsy led to a diagnosis of RDD, and immunohistochemistry was useful for diagnosing RDD. A systemic treatment with steroids improved his symptoms, including the neck mass. Physicians need to consider the diagnostic difficulty associated with extranodal soft tissue RDD as well as its rarity.