Introduction. Renal replacement lipomatosis (RRL) – a disease manifested by the expansive proliferation of adipose tissue of the renal sinus, spreading to the perinephric tissue with an increase in its mass, as well as atrophy of the renal parenchyma and a sharp dysfunction of the kidney, is a complication of chronic, long-term, calculous pyelonephritis. RRL can mimic high fat kidney tumor.

Description of the clinical case. A 70-year-old patient has been suffering from urolithiasis for more than 25 years. Operated twice on the left kidney. Was admitted with the clinic of acute pyelonephritis on the left, persistent fistula in the lumbar region with background of diabetes mellitus. General clinical and special examinations were carried out. Nephrectomy in the left side was performed. Microscopic examination – chronic active pyelonephritis with nephrosclerosis and parenchymal atrophy, adipose tissue with extensive fields of fibrosis and chronic inflammation.

Discussion. Prolonged course of the inflammatory process in the kidney, coral kidney stone, accelerated ESR (67 mm/h) and the results of computed tomography (CT) and magnetic resonance imaging (MRI) a powerful overgrowth of adipose tissue surrounding the kidney and pronounced lipomatous pedunculitis – made it possible to think about changes in the perinephric tissue in the form of RRL. The main sign of RRL according to the results of CT and MRI is pyonephrosis with atrophy of the renal parenchyma, fragmentarily replaced by fatty proliferating tissue, spreading from the sinus of the kidney and capturing all perirenal tissue with an increase in its mass.

Conclusion. An increase in the volume of adipose tissue in the renal sinus and an increase in the volume of perirenal tissue according to CT or MRI data in patients with calculous pyonephrosis should be considered a sign of renal replacement lipomatosis.