Xanthogranulomatous pyelonephritis (gross pathology)

MACROSCOPIC DESCRIPTION: Sectioning of the kidney reveals a lesion at the superior pole, 33x18x18mm, with a soft, mottled, tan, focally cystic cut surface.  It is well delineated from the adjacent renal parenchyma and expands but does not infiltrate the overlying capsule, from which it is readily dissected.  The lesion shows no invasion into the renal pelvic fat.  No other tumor or lymph nodes are identified.

MICROSCOPIC DESCRIPTION: Sections of the kidney show features of xanthogranulomatous pyelonephritis.  The area is relatively ill-defined.  There are many foamy and pigment-laden macrophages with lymphocytes and plasma cells. Spindled reactive fibroblasts are seen and they form vague short fascicles, intermixed with the inflammatory cells.  There is no evidence to suggest malakoplakia.  The inflammation extends into the interstitium.  Acute inflammation is inconspicuous.  There are no granulomas.  No evidence of necrosis is seen.  The glomeruli adjacent to the inflammatory areas are globally sclerosed.  No tumor is identified.  There are a few cystic locules, which are lined by flattened-to-cuboidal epithelium with no atypia.  Occasional cholesterol clefts are identified, surrounded by multinucleated giant cells.  The remaining renal parenchyma is unremarkable. 

FINAL DIAGNOSIS: Xanthogranulomatous pyelonephritis.