Histiocytoid melanoma presenting as lymphadenopathy and mimicking Rosai-Dorfman disease.
Stephen J Babcock, Valentina Nardi
✦ AI-curated · Sources linked
Case in brief
A patient presented with large, unilateral inguinal lymphadenopathy. Excisional biopsy showed expanded lymph-node sinuses containing large cells with abundant granular eosinophilic cytoplasm, eccentric nuclei, and prominent nucleoli, alongside reactive sinus histiocytes. The morphology raised suspicion for Rosai-Dorfman disease, but emperipolesis was absent. Immunohistochemical work-up identified the atypical infiltrate as metastatic melanoma with histiocytoid morphology.
What made this case unusual
Metastatic melanoma in the lymph node had histiocytoid morphology that mimicked Rosai-Dorfman disease, with reactive sinus histiocytes also present.
Diagnostic / clinical pearl
When histiocytoid cells expand lymph-node sinuses, morphology alone may suggest Rosai-Dorfman disease; immunohistochemistry can distinguish metastatic melanoma, particularly when emperipolesis is absent.