Review of sinus histiocytosis with massive lymphadenopathy (Rosai-Dorfman disease) of head and neck.

The entity known as sinus histiocytosis with massive lymphadenopathy (SHML), or Rosai-Dorfman disease (RD disease), is an uncommon benign proliferation of hematopoietic and fibrous tissue that often presents in the head and neck region. Its initial manifestations most often include a roughly symmetric, painless, bilateral cervical adenopathy, although extranodal disease may develop in a minority of patients. The key histologic feature of SHML is the presence of various numbers of large, pale histiocytic cells that contain within their cellular borders apparently engulfed lymphocytes ("emperipolesis"); these distinctive large, pale cells - RD cells - are S-100 protein-positive by immunostaining and so differ from ordinary histiocytes. Despite its sometimes impressive clinical presentation, SHML is a benign and self-limited disease, whose treatment is aimed largely at controlling its local manifestations (most often by surgical therapy). The microscopic differential diagnosis, particularly in extranodal disease, is at times challenging and can include Langerhans' cell histiocytosis, Hodgkin's disease, non-Hodgkin's lymphoma, metastatic carcinoma, and metastatic malignant melanoma.