Extranodal Rosai-Dorfman Disease with Bilateral Renal Involvement Mimicking Lymphoma — Lahore, Pakistan

Key finding

> Renal biopsy told a different story: sheets of large histiocytes displaying emperipolesis, immunohistochemically positive for S100 and CD68 — Rosai-Dorfman disease, not lymphoma. Extranodal involvement occurs in a significant proportion of Rosai-Dorfman disease cases, but renal manifestations are rare and — as this case demonstrates directly — imaging characteristics of RDD-involved kidneys can be functionally indistinguishable from malignant renal or lymphomatous infiltration on both CT and PET-CT. Only histopathology broke the diagnostic tie.

Framework connections: The Immune Priming, The Undersized Filter (Renal-Metabolic)

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