FINAL DIAGNOSIS: Extranodal Rosai-Dorfman Disease
Sinus histiocytosis with massive lymphadenopathy (Rosai-Dorfman disease; RDD) was originally described by Rosai and Dorfman in 1969. Since then extranodal involvement (skin, soft tissue, bone and nasal mucosa) has been shown to be present in 43% of patients with nodal RDD. However, extranodal RDD without concomitant nodal disease is extremely rare. Patients with isolated soft tissue RDD tend to be older with a female predominance. The chief complaint is usually a slowly growing mass without pain or tenderness. The common clinical presentations characterized by nodal RDD (fever, lymphadenopathy, leukocytosis, anemia, elevated erythrocyte sedimentation rates and polyclonal hypergammaglobulinemia) are usually not present.
Grossly, the lesions of soft tissue RDD are firm, poorly or well demarcated, with a nodular cut surface and yellow to ivory-tan color. Sizes range from 1 to 10 cm. Microscopically, the lesions consist of sheets of large, pale histiocytes punctuated by scattered lymphoid aggregates. A vague storiform pattern is frequently observed because of the presence of abundant collagen bundles. The histiocytes have round to oval vesicular nuclei and often small nucleoli, with abundant clear or eosinophilic cytoplasm. The cytoplasm of the histiocytes may contain lymphocytes (emperipolesis), although this is less striking than the lesions of lymph nodes. Mature small lymphocytes and plasma cells are frequently scattered throughout the lesions as single cells or in aggregates. The histiocytes strongly express S-100 protein in virtually all cases, and also stain with the histiocytic marker CD68, a-1-antitrypsin and a-1-antichymotrypsin.
RDD of soft tissue can be more difficult to recognize than its lymph node counterpart. Emperipolesis is less conspicuous, collagen deposition arranged in a storiform pattern can be prominent, and there are usually scattered lymphoplasmacytic cells or aggregates. Differential diagnoses include inflammatory pseudotumor, benign and malignant histiocytomas, xanthogranuloma, lymphoma, and Langerhan's cell histiocytosis. Recognition of the typical histiocytes with emperipolesis and confirmatory staining with S-100 should facilitate the correct diagnosis.
The pathogenesis of RDD is unknown. The clinical course is generally benign. Most patients with isolated soft tissue RDD remained asymptomatic following surgery, although some developed recurrent disease.
Contributed by Su Zheng, MD, PhD and Uma Rao, MD