Diagnose This (January 25, 2021)

What is the name of the finding at the end of the arrow and what condition is it classically associated with?

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Answer: The light microscopic image shows a portion of a non-necrotizing granuloma comprised of histiocytes with giant-cell formation and intermixed lymphoplasmacytic inflammation. At the end of the arrow is what is known as an “asteroid body” which is classically associated with sarcoidosis; however, these are by no means specific for sarcoid as asteroid bodies have been seen in many other conditions including infections, various malignancies, foreign body granulomas, cysts (i.e. dermoid, sebaceous), etc. Overall, the biopsy in this case demonstrated a dense granulomatous tubulointerstitial nephritis which after clinical exclusion of other causes (i.e. infection, drug/hypersensitivity) were compatible with the patient’s known prior history of sarcoidosis.