AJR:189, September 2007 W163 AJR 2007; 189:W163–W165 0361–803X/07/1893–W163 © American Roentgen Ray Society Soussan et al. CT of Renal Lipolysis Genitourinary Imaging • Case Report Fat–Fluid Levels in Renal Caliceal Cavities: A CT Sign of Lipolysis Due to Urine Extravasation After Kidney Rupture Michaël Soussan 1 Isabelle Boulay-Coletta 1 Vincent Molinié 2 Walid Alamé 3 Marc Zins 1 Soussan M, Boulay-Coletta I, Molinié V, Alamé W, Zins M Keywords: CT, genitourinary tract imaging, kidney, lipolysis DOI:10.2214/AJR.05.0866 Received May 23, 2005; accepted after revision July 20, 2005. 1 Department of Radiology, Saint Joseph Hospital Foundation, 185 rue Raymond Losserand, 75014 Paris, France. Address correspondence to I. Boulay-Coletta (iboulay@hopital-saint-joseph.org). 2 Department of Pathology, Saint Joseph Hospital Foundation, Paris, France. 3 Department of Urology, Saint Joseph Hospital Foundation, Paris, France. WEB This is a Web exclusive article. rine extravasation is a rare com- plication of urinary tract obstruc- tion. Urine leaks out of tears in the caliceal fornix and, more rarely, the renal pelvis or ureter. In exceptional cases, urine leaks through perforations in the renal wall. Lipolysis of perihilar tissues occurs within a few days of urine extravasation [1]. We describe caliceal fat–fluid levels visual- ized on CT in a patient who had chronic ob- structive pyelonephritis complicated by ex- tensive kidney rupture with extravasation of infected urine. We suggest that urine-induced lysis of perirenal fat may have caused this CT finding. To our knowledge, this is the first report of fat–fluid levels in renal calices. Case Report A 57-year-old man was admitted to our emergency department with a 2-week his- tory of left flank pain, malaise, fever (38.1°C), asthenia, and anorexia. He had a history of untreated type 2 diabetes. Cutane- ous erythema over the left lumbar area and hemodynamic instability were found at physical examination. Helical CT (Light- Speed Pro 16, GE Healthcare) of the abdo- men and pelvis was performed immediately with and without iodinated contrast material and delayed scanning. An 8-mm stone ob- structing the distal portion of the left ureter was seen, as were diffuse pelvicaliceal dila- tation and extensive perirenal and pararenal fluid collections. The left kidney was dif- fusely enlarged (length, 15 cm), and an ex- tensive parenchymal tear was seen in the up- per pole (Figs. 1A and 1B). Fat–fluid levels were visible in most of the dilated calices and in the pelvis. Density was –100 H for the top component and 10 H for the bottom com- ponent (Fig. 1C). A fat–fluid level was also seen in the bladder (Fig. 1D). Enhancement was less marked in the left than the right kid- ney, and excretion was asymmetric. Blood test abnormalities included leukocy- tosis (WBC count, 22,000/mm 3 ) with predom- inance of neutrophils (18,000/mm 3 ), C-reactive protein elevation (312 mg/L), hyperglyce- mia (17.8 mmol/L), and hyponatremia (123 mmol/L). The hemoglobin concentration was 10.3 g/dL, and the hematocrit was 27%. The serum creatinine concentration was normal. Urine and blood culture results were positive for β-hemolytic streptococci. Although the urine was turbid and orange to the naked eye, test results were negative for cholesterol and triglycerides. IV antibiotics were given, a ureteral catheter was inserted, and 1 L of pus was drained surgi- cally from the perirenal region. The left kidney showed no evidence of function and was re- moved surgically 2 weeks later. The renal cal- ices were dilated and filled with pus. Histo- logic examination of the kidney showed not only chronic tubulointerstitial pyelonephritis with lymphoplasmacytic infiltrates but also foci of acute pyelonephritis with neutrophilic infiltrates. There was no necrosis of the renal fat sinus. Within the perirenal tissue, foci of li- polysis with marked inflammation and granu- loma formation were seen. The granuloma was composed of foamy macrophages and of neu- trophilic infiltrates containing multinucleate giant cells and lymphocytes (Fig. 1E). Ulcers without perforation were visible in the pelvi- caliceal urothelium, and necrotic fatty tissue was found in the caliceal lumens (Fig. 1F). There was no histologic evidence of xan- thogranulomatous pyelonephritis (XGP). Discussion The incidence of spontaneous extravasa- tion of urine related to ureteral stone obstruc- tion has been estimated at 4% in patients un- dergoing excretory urography [2]. Urine extravasation occurs when elevation of pres- sure in the renal pelvis causes urine to flow in the retrograde direction through the intersti- U Downloaded from www.ajronline.org by 52.73.204.196 on 05/13/22 from IP address 52.73.204.196. Copyright ARRS. For personal use only; all rights reserved