1Department of Radiology, GATA Haydarpaşa Training Hospital, Istanbul, Turkey; 2Division of Radiology, Kasımpaşa Military Hospital, Istanbul, Turkey *Corresponding Author e-mail: draksivrioglu@gmail.com ظهور األستبدال الشحمي الكلوي يف التصوير املقطعي شبه ورم نادر كمال كارا، علي كمال �سيفريوجلو، كو�سكون اأوزتوركر، جاهد كافادار Appearance of Renal Replacement Lipomatosis on Computed Tomography Rare pseudotumour Kemal Kara,1 *Ali K. Sivrioglu,2 Coskun Oztürker,1 Cahit Kafadar1 An 81-year-old male patient presented to the Urology Department of GATA Haydarpaşa Training Hospital, Istanbul, Turkey, in May 2014 complaining of left lumbar pain and a sense of abdominal fullness. On physical examination, left lumbar tenderness and a palpable mass were observed. A urine analysis showed an increased number of red blood cells. Plain abdominal radiography demonstrated soft tissue density at the left upper quadrant pushing the colon segments medially [Figure 1]. Abdominal ultrasonography revealed a significant increase in the size and echogenicity of the left kidney and its margin could not be clearly differentiated from the surrounding fat tissue. In addition, a decrease in the left renal parenchymal thickness was noted. Computed tomography (CT) and magnetic reso- nance imaging (MRI) were performed without the administration of intravenous contrast due to elevated serum creatinine levels. The CT scan [Figure 2] and axial T2-weighted MRI images revealed a fatty mass in the left kidney (approximately 22 x 18 x 14 cm in Figure 1: Plain abdominal radiograph showing a mass with soft tissue density in the left upper quadrant pushing the colon segments medially (arrows) in a patient with renal replacement lipomatosis. interesting medical image Sultan Qaboos University Med J, November 2015, Vol. 15, Iss. 4, pp. e567–568, Epub. 23 Nov 15 Submitted 5 Nov 14 Revision Req. 11 Jan 15; Revision Recd. 22 Feb 15 Accepted 11 May 15 doi: 10.18295/squmj.2015.15.04.024 Appearance of Renal Replacement Lipomatosis on Computed Tomography Rare pseudotumour e568 | SQU Medical Journal, November 2015, Volume 15, Issue 4 Interesting Medical Image | e568 liposarcomas and angiomyolipomas should be considered in the differential diagnosis for RRL. XGP is defined as a chronic granulomatous inflammatory disorder of the kidney that is characterised by microscopic lipid-laden foamy macrophages.4 For patients with this condition, CT scans show xantho- granulomatous hypodense regions in the renal cortex and medulla, reduced renal function, detection of staghorn calculi, hydronephrosis and pyonephrosis.4 Malakoplakia is a rare inflammatory disorder that may affect the kidneys. This condition is characterised by foamy histiocyte accumulation in the renal parenchyma and may represent a variant of XGP.2 Lipomas and liposarcomas are generally seen in the intrarenal or extrarenal regions, outside of the renal sinus. Liposarcomas should be considered if the lesion has irregular borders and invasion of the surrounding structures or if heterogeneity or a mass effect are present.5 Angiomyolipomas are generally seen in patients with tuberous sclerosis; they are differentiated by the presence of normal renal function and the absence of renal calculi on CT scans. The complications of RRL generally include perirenal abscesses and fistulae.1 In conclusion, RLR is a rare condition that should be considered in the presence of significant perirenal and intrarenal fatty infiltration. Early recognition of this condition would avoid unnecessary medical and surgical treatment. CT scans are an effective imaging modality in the diagnosis and follow-up of this condition. References 1. Tunçbilek İ, Ünlübay D, Kacar M, Bilaloğlu P. [Lipomatous of renal replacement: US and CT findings.] Diagn Interv Radiol 2002; 8:82–4. 2. Ginat DT, Bhatt S, Dogra VS. Replacement lipomatosis of the kidney: Sonographic features. J Ultrasound Med 2008; 27:1393–5. 3. Sönmez G, Mutlu H, Özturk E, Sıldıroğlu O, Akyol İ, Başekim CÇ, et al. Replacement lipomatosis of the kidney: MRI features. Eur J Gen Med 2008; 5:184–6. 4. Başara I, Akın Y, Serter S, Bozkurt A, Nuhoğlu B. [Renal sinus lipomatosis.] Kafkas J Med Sci 2013; 3:48–54. doi: 10.5505/ kjms.2013.72473. 5. Nicholson DA. Case report: Replacement lipomatosis of the kidney - Unusual CT features. Clin Radiol 1992; 45:42–3. doi: 10.1016/S0009-9260(05)81469-2. size) with areas of linear and patchy fibrous tissue. The mass caused significant enlargement of the left kidney and distortion of the surrounding structures. There were no areas of restricted diffusion within the lesion on diffusion-weighted images. A biopsy of the mass was performed and a pathological examination revealed mature fat tissue. As a result of these findings, the left renal mass was considered to indicate renal replacement lipomatosis (RRL). Ultrasonography performed three months after the initial diagnosis revealed no changes in the size and imaging characteristics of the lesion. Comment RRL is a marked proliferation of fat within the renal sinus and perirenal region where the renal parenchyma is replaced by fatty tissue.1 While renal sinus lipomatosis is a mild proliferation of fatty tissue in the renal sinus, RRL is considered to be an advanced or aggressive form of renal sinus lipomatosis.2,3 The condition is the result of severe atrophy of the renal parenchyma and fatty proliferation and is usually accompanied by chronic infections, obstructive kidney stones and long-standing hydronephrosis. It generally occurs unilaterally, contrary to renal sinus lipomatosis, and extends to the perirenal and periureteral areas.3,4 Calculi are also seen in approximately 70% of cases.3 Xanthogranulomatous pyelonephritis (XGP), malakoplakia and tumours including fat-like lipomas, Figure 2: Non-contrast computed tomography show- ing a fatty renal mass (arrows) in a patient with renal replacement lipomatosis. The mass caused significant left renal enlargement and distortion on the surround- ing structures. Kemal Kara, Ali K. Sivrioglu,Coskun Oztürker and Cahit Kafadar http://dx.doi.org/10.5505/kjms.2013.72473 http://dx.doi.org/10.5505/kjms.2013.72473 http://dx.doi.org/10.1016/S0009-9260%2805%2981469-2