This transcript provides a microscopic overview of Rosai-Dorfman Disease (RDD), also known as sinus histiocytosis with massive lymphadenopathy, focusing primarily on its presentation in soft tissue. At low power, the disease displays a characteristic "pink and blue" pattern, consisting of sheets of pale histiocytes interspersed with blue nodules of lymphoid cells. The high-power diagnosis relies on identifying large, distinct histiocytes possessing abundant pale cytoplasm, large nuclei, and prominent central nucleoli. Although often cited as the defining feature, the presence of emperipolesis—the engulfment of intact lymphocytes and plasma cells by the histiocytes—is noted to be often subtle, difficult to find perfectly, and non-specific, making the overall cytomorphology the most crucial diagnostic element. Immunohistochemically, the histiocytes of RDD are typically strongly positive for S100.
Rosai-Dorfman Disease: Pathological Features and Diagnosis
0:05 Nomenclature: Rosai-Dorfman Disease (RDD), also known as sinus histiocytosis with massive lymphadenopathy, is often encountered by the speaker in soft tissue presentations, rather than solely in lymph nodes.
0:18 Low Power Appearance: RDD typically exhibits a "pink and blue" appearance, characterized by sheets of pale pink/gray histiocytes (the RDD cells) punctuated by blue nodules of lymphocytes and plasma cells, sometimes including germinal centers.
0:48 Clinical Presentation: Cases are often seen as subcutaneous nodules, commonly on young adults (e.g., 20-year-old women), and are frequently clinically misdiagnosed as cysts.
1:16 High Power Cytomorphology (Key Diagnostic Feature): Diagnosis relies on identifying large, prominent histiocytes with abundant pale cytoplasm, large nuclei with pale chromatin, and prominent central nucleoli. These histiocytes often appear to blend together into a syncytium.
2:04 Emperipolesis (The Buzzword): Emperipolesis, defined as intact white or red blood cells contained within vacuoles in the histiocyte cytoplasm, is the classic, though often subtle, buzzword finding. The speaker stresses that finding perfect emperipolesis is difficult and often unnecessary to make the diagnosis, as the overall cellular morphology is more reliable.
3:01 Differential Diagnosis: Emperipolesis is not specific to RDD; it can also occur in Juvenile Xanthogranuloma (JXG) and even some sarcomas.
3:11 Immunohistochemistry (IHC): The histiocytes in RDD are usually strongly positive for S100 in both the nucleus and cytoplasm, which can also help highlight the vacuoles associated with emperipolesis.