Renal interstitial granulomas Renal interstitial necrotizing granulomas Renal interstitial necrotizing granulomata An organized collection of histiocytes (specifically macrophages) localized in the interstitial tissue of the kidney. Through light microscopy, the activated histiocytes appear as epithelioid cells with round to oval nuclei, often with irregular contours and abundant granular eosinophilic cytoplasm with indistinct cell borders. They may also coalesce to form multinucleated giant cells. Granulomas may be associated with a peripheral cuff of lymphoplasmacytic and occasionally eosinophilic inflammation. Organization can range from poorly-to-well defined. Granulomas can present as necrotizing or non-necrotizing. Microscopically, necrotizing granulomas distinctly have central necrosis with a palisaded lymphohistiocytic reaction and a cuff of chronic inflammation. Granulomatous inflammation is a distinctive form of chronic inflammation produced in response to various infectious, autoimmune, toxic, allergic, and neoplastic conditions.