Light micrograph of kidney biopsy of a patient with granulomatous acute interstitial nephritis

Light micrograph shows granulomatous change in acute interstitial nephritis. The interstitial infiltrate is seen on the left, while the granuloma is on the right. The granuloma consists of both giant cells (arrows) and epithelioid cells with abundant cytoplasm, which has an amorphous red appearance. Although these findings are characteristic of sarcoid involvement in the kidney, they can be seen with any cause (drug or infection) of acute interstitial nephritis.