BACKGROUND: Xanthogranulomatous pyelonephritis (XP) is an extremely rare, severe, atypical form of chronic renal parenchymal inflammation accompanied by hydronephrosis and/or urolithiasis. The pathomechanism of XP is not yet fully understood. Microscopically, XP is indicated by the presence of multinucleated giant cells and lipid-laden macrophages, as well as inflammatory infiltration and intensive renal fibrosis. The lipid accumulation in kidney parenchyma may be secondary to the altered flow of low-density lipoprotein (LDL)-derived cholesterol particles inside the affected cells. Physiologically, the process of LDL-derived cholesterol transport from lysosomes to the sites of its esterification is dependent on vimentin, which is a molecule comprising the cytoskeleton in mesenchymal cells.

CASE REPORT: A 7-year old girl was hospitalized because of the finding of unexplained kidney lesions on an abdominal ultrasound examination (an enlarged and deformed collecting system of the right kidney with hyperechogenic, solid, staghorn lesions in the calyces). Three months earlier, the patient had experienced recurrent urinary tract infection. Based on the subsequent laboratory and imaging diagnostics, the final diagnosis of XP was established and the girl was qualified for right-sided nephrectomy Microscopic examination revealed numerous foci of granuloma formations with no evident exponents of dysplastic or neoplastic abnormalities. Significant CD68-positive cell infiltrations and scattered foam cells arranging the numerous foci of granuloma inflammation were noticed. Renal parenchyma, adjacent to granuloma lesions, presented a vimentin expression.

CONCLUSIONS: Vimentin expression in XP may confirm a focal character of chronic granuloma formation and may suggest the complexity of XP pathogenesis involving not only macrophage and fibroblast activation but also local lipid deregulation and fibrosis.

Keywords: Nephritis, Interstitial, Pyelonephritis, Xanthogranulomatous