CT scan of Right Kidney demonstrates low density rounded areas throughout the affected kidney, these are often referred to as the ‘bear paw’ sign which results from the replacement of the renal parenchyma (normal kidney tissue) by an infectious process which produces masses in the typical pattern seen above, this pattern is reflective of hydronehprosis. (Hydronephrosis is an enlargement or swelling of the kidney with a corresponding inability to drain urine into the bladder). Also evident is a large, central ‘staghorn calculus’; this is a branched renal calculus (kidney stone) that resembles the antlers of a stag. A staghorn calculus is an indication of chronic or repetetive urinary tract infections (UTI’s). Also present are enlarged inflammatory periaortal and pericaval lymphnodes. Findings: Xanthogranulomatous Pyelonephritis in a 64 year old female patient.
Xanthogranulomatous pyelonephritis (XGP) is a serious chronic inflammatory disease of the kidneys. Pyelonephritis alone simply means an inflammation of the parenchyma (the kidney tissue) calyces (the renal chambers of the kidney through which urine passes) and the pelvis, due to an infection, usually bacterial.(1) Xanthogranulomatous Pyelonephritis is a less common form of pyelonephritis whereby inflamed, infected tissue (granulomatous abcesses) gradually forms and replaces the normal kidney tissue (parenchyma) causing severe kidney destruction resulting in a lack of function of the affected kidney(s). In most cases there is little, if any, renal function in the affected kidney.(2) Another common occurrence are kidney stones especially staghorn calculus or calculi (as seen in Image 1). The majority of recorded cases of Xanthogranulomatous Pyelonephritis affect only one kidney, although bilateral disease has been observed but is very rare.(3) Bacterial infection is common on laboratory testing of urine cultures and the two most often identified infections are Escherichia Coli and Proteus Mirabilis.(4)
Xanthogranulomatous Pyelonephritis presents itself in two ways, either diffuse or focal. The diffuse presentation occurs in 90% of cases and means the inflammation is evident over a widespread area. Focal presentation is less common occurring in only 10% of cases and means the inflammation occurs in a specific location. Xanthogranulomatous Pyelonephritis is a rare condition and is a complication of around 1% of all renal infections. Xanthogranulomatous Pyelonephritis was first described in 1916 by Schlagenhaufer and since then there have been over 400 known cases worldwide.(5) Xanthogranulomatous Pyelonephritis has been observed in all age groups but is more common in the middle aged to elderly categories. Due to the relatively uncommon occurrence, Xanthogranulomatous Pyelonephritis can be notoriously difficult to diagnose and is often confused with renal cell carcinoma or other inflammatory diseases such as tuberculosis.
2. Craig WD, Wagner BJ, Travis MD. Pyelonephritis: radiologic-pathologic review. Radiographics. 28 (1): 255-77.
3. Eastham J, Ahlering T, Skinner E. Xanthogranulomatous pyelonephritis: clinical findings and surgical considerations. Urology 1994;43:295–9 .
4. Parwani AV ‘Xanthogranulomatous pyelonephritis’ Arch Pathol Lab Med. 2011 May;135(5):671-4. doi: 10.1043/2009-0769-RSR.1.
5. Tolio., B. M., Iloreta, A., Freed, S. Z., Fruchtman, B., Bennett, B. and Newman, H. R.: Xanthogranulomatous pyelonephritis: Detailed analysis of 29 cases and a brief discussion of atypical presentations. J. Urol., 126: 437-442, 1981