British Journal of Radiology (2005) 78, 60-61
© 2005 British Institute of Radiology
doi: 10.1259/bjr/31723131
Renal replacement lipomatosis associated with renal transplantation
S D Chang, MD1,
F V Coakley, MB BCh2 and
R B Goldstein, MD2
1 Department of Radiology, University of British Columbia, Vancouver Hospital & Health Sciences Centre, 899 West 12th Avenue, Vancouver, BC, Canada V5Z 1M9 and 2 Department of Radiology, University of California San Francisco, 505 Parnassus Avenue, San Francisco, CA 94143-0628, USA
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Abstract
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We report a case of extensive renal replacement lipomatosis demonstrated by ultrasound (US) and computed tomography (CT) in a 57-year-old woman with a history of two cadaveric renal transplants. One transplant was non-functional due to chronic rejection. The second renal transplant is functioning normally and the renal replacement lipomatosis did not cause mass effect on either of the renal transplants.
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Introduction
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Renal replacement lipomatosis (RRL) is the benign proliferation of fibrofatty tissue replacing renal parenchyma that has atrophied. In most cases, there is severe destruction of the renal parenchyma with fibrofatty tissue replacement and the extent of the proliferation can involve the renal sinus, renal hilum and perirenal space. However, cases with focal involvement of the renal tissue can also occur. RRL is usually a result of chronic inflammation and in greater than 70% of cases, it is associated with calculus disease [1, 2]. We report a case of extensive renal replacement lipomatosis in a patient who had received two cadaveric renal transplants. Possible aetiological factors are discussed.
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Case report
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A 57-year-old woman was admitted for evaluation of an enterocutaneous fistula, which had developed as a complication of a right colectomy performed for carcinoma of the colon 3 months previously. Her past medical history was notable for a 21 year history of insulin-dependent diabetes mellitus. Her past surgical history included cadaveric renal transplantation for end-stage urate nephropathy 10 years previously. This transplant failed due to rejection and a second transplant was performed 2 years later. Since transplantation, the patient had been successfully maintained on corticosteroids, Cyclosporin and Imuran, with no evidence of rejection in the second transplant. Findings on physical examination included severe truncal obesity, a right lower quadrant ileostomy and an enterocutaneous fistula.
CT was performed for assessment of the enterocutaneous fistula. Unexpectedly, CT showed fat deposition in the renal sinus and hilum replacing most of the atrophic native kidneys. There was extensive fatty proliferation of the perirenal space with marked anterior and medial displacement of the bowel (Figure 1
). A functioning renal allograft was present in the left iliac fossa and an atrophic non-functioning allograft in the right iliac fossa. Both of these renal transplants were not affected by the extensive RRL. A subsequent ultrasound (US) performed to evaluate the renal transplant, also showed extensive retroperitoneal fat. The pancreas and native kidneys were not visible at US owing to the extensive retroperitoneal fat deposition. A follow-up CT performed 1 year later showed no change in the appearance of the extensive renal replacement lipomatosis.
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Figure 1. A 57-year-old woman with extensive renal replacement lipomatosis following two cadaveric renal transplants and on long-term steroid therapy. CT shows extensive deposition of fat in the retroperitoneum surrounding and replacing most of the native atrophic kidneys (curved arrows). Mass effect on the bowel loops (straight arrows) is also demonstrated.
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Discussion
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RRL is a rare condition characterized by the proliferation of the renal sinus, renal hilum and perirenal fatty tissue with replacement of the atrophic renal parenchyma. The extent of this disease is variable. A milder and more common form of this entity involving the renal sinus is referred to as renal sinus lipomatosis. Fibrofatty proliferation of the renal sinus, renal hilum, and/or perirenal space can also occur with obesity, Cushing's syndrome, corticosteroid excess or be idiopathic but there is usually preservation of the renal parenchyma which helps to distinguish these entities from RRL [3, 4]. In RRL, there is fatty replacement of the atrophic/destroyed renal tissue and usually a history of chronic inflammation and stone disease [1, 2]. The clinical presentation of RRL is non-specific and variable. Patients may have a history of urinary tract infection, flank pain, weight loss, haematuria, fever or palpable mass [5]. Occasionally, they can be asymptomatic. RRL can simulate a soft tissue neoplasm on plain film and hydronephrosis or xanthogranulomatous pyelonephritis (XGPN) with contrast radiography. The advent of US and particularly CT, allows for direct visualization and can reliably distinguish adipose tissue from other soft tissue masses. CT is the best imaging modality to diagnose RRL and differentiate it from other fat containing lesions such as renal angiomyolipomas, retroperitoneal lipomas and liposarcomas [6]. Angiomyolipomas are usually well-circumscribed, focal intrarenal or extrarenal masses. Lipomas are well circumscribed and encapsulated. Liposarcomas may be well circumscribed or infiltrative, but are characteristically identified by the presence of internal thick soft tissue strands or nodules. And in all three of these entities, renal function is expected to be preserved and they are not usually associated with chronic inflammation and stone disease. CT can also differentiate RRL from XGPN and hydronephrosis. In all three of these conditions, an associated calculus may be seen. In RRL, the kidney is atrophic and replaced with fatty tissue whereas in XGPN, the renal outline is generally preserved and enlarged and true fat density is usually not seen [7, 8].
Our case of extensive fat deposition replacing most of the atrophic native kidneys and extensive proliferation around the native kidneys in a patient with a history of end-stage renal disease is compatible with renal replacement lipomatosis. To our knowledge the severity in this case and the association with renal transplantation has not been previously reported. The extensive involvement also suggests more than one aetiological factor may be involved and are subsequently discussed.
Hypoechogenicity of the perinephric fat has been described in 13.5% of renal transplant recipients [9] and probably reflects reduced water content [10, 11]. These findings suggest the perinephric fat around the native kidneys of renal transplant recipients may be different from adipose tissue elsewhere in the body. While the nature of these differences is unclear, they may account for the extensive distribution of lipomatosis seen in our patient. Long-term steroid administration may also be a factor in the development of lipomatosis, although a perinephric pattern of lipomatosis is not characteristic of the fatty proliferation seen in Cushing's syndrome.
A potential criticism of this report is the lack of pathological correlation. However, the diagnosis of renal replacement lipomatosis is essentially radiographic. Biopsy of lipomatosis demonstrates unremarkable mature adipose tissue and may contain fibrous tissue, and does not contribute to the diagnosis of lipomatosis, which depends on the demonstration of abnormal fatty accumulation by imaging.
In summary, we report a case of extensive renal replacement lipomatosis in a patient with a history of renal transplantation and previous urate nephropathy. This extensive pattern of RRL may be also be attributed by the distinct properties of the perinephric fat after renal transplantation and long term corticosteroid usage.
Received for publication April 7, 2004.
Revision received July 21, 2004.
Accepted for publication September 9, 2004.
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References
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Abstract
Introduction
