Primary Rosai-Dorfman disease of bone arising in the infantile ilium: A case report.

Rosai-Dorfman disease (RDD) is an extremely rare benign histiocytic disorder that usually affects young adults. Extranodal involvement of the RDD is common and may occur in >40% of patients, but bone involvement occurs in <10% of cases. Furthermore, primary bone RDD is extremely rare. The present study reports a case of primary bone RDD arising in the infantile ilium. Plain radiographs and computed tomography (CT) revealed an osteolytic lesion at the peri-acetabular region of the patient's right ilium. Fluorodeoxyglucose positron emission tomography indicated an abnormal accumulation only in the right iliac bone, without any other accumulation. An open biopsy was performed and the diagnosis of primary RDD of bone in the ilium was made. The bone lesion exhibited spontaneous regression on radiography, and the patient was able to walk without any limping or pain at 8 months after the biopsy. After 18 months of follow-up, the bone lesion had completely disappeared, and no joint deformity was observed on radiography or CT. The present report described the clinicopathological details of this rare case and reviewed the relevant literature.