Question

What is the diagnosis in a 65 year old patient with fever, flank pain, and calculi with fat densities?

• A. Xanthogranulomatous pyelonephritis
• B. Renal abscess
• C. Chronic pyelonephritis
• D. Tuberculous kidney

Hint:

Fat-dense areas around an obstructing stone with chronic infection point to a specific destructive kidney disease.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
A 65 year old patient has fever, pain in the flank, and kidney stones that show fat density on imaging. We need to name the disease that fits this exact picture.

Step 2: Key Concept:
Xanthogranulomatous pyelonephritis (XGP) is a rare, severe form of chronic kidney infection. It destroys the kidney tissue and replaces it with lipid laden (fat filled) macrophages, called foam cells. This fat content is what shows up as fat density areas on CT scan. XGP is almost always linked to an obstructing stone, often a staghorn calculus, along with long standing infection, commonly by Proteus or E. coli.

Step 3: Detailed Explanation:
The three clues, fever, flank pain, and a stone with fat density, point straight to XGP. On CT, XGP classically shows an enlarged kidney with a central stone, dilated calyces filled with pus and debris, and surrounding fat dense material, sometimes called the "bear paw" sign.
Renal abscess also causes fever and flank pain, but it does not typically show a fat containing mass around a stone, it shows a fluid filled cavity with a thick wall.
Chronic pyelonephritis causes scarring and a small shrunken kidney with cortical thinning, not a fat density mass.
Tuberculous kidney causes calcification, cavitation, and a "putty kidney" in advanced cases, but not fat density change.

Step 4: Final Answer:
The fat density change around an obstructing calculus with fever and flank pain is the hallmark of xanthogranulomatous pyelonephritis.