|Year : 2014 | Volume
| Issue : 2 | Page : 428-430
Idiopathic renal replacement lipomatosis: A rare renal pseudo tumor
Shailja P Wahal, Kavita Mardi
Department of Pathology, Indira Gandhi Medical College, Shimla, Himachal Pradesh, India
|Date of Web Publication||14-Jul-2014|
Shailja P Wahal
Department of Pathology, Indira Gandhi Medical College, Shimla, Himachal Pradesh - 171 001
Source of Support: None, Conflict of Interest: None
Renal replacement lipomatosis (RRL) is a rare condition that occurs as an end result of renal atrophy or destruction of renal parenchyma by excessive lipomatous tissue in renal sinus and perinephric space. We report a case of RRL presenting as a right renal mass clinically. Intra-venous pyelography and renal scan revealed a left non-functioning kidney. A left nephrectomy was performed. After histopathological examination and extensive literature search, a diagnosis of RRL was given. In majority of cases, it is associated with renal calculi. Idiopathic variety is not common. It is a rare entity and the diagnosis may be missed due to lack of experience. It has to be differentiated from other fat-containing tumors such as renal lipoma, xanthogranulomatous pyelonephritis, angiomyolipoma and liposarcoma.
Keywords: Idiopathic, renal replacement lipomatosis, renal
|How to cite this article:|
Wahal SP, Mardi K. Idiopathic renal replacement lipomatosis: A rare renal pseudo tumor. J Can Res Ther 2014;10:428-30
| > Introduction|| |
Renal replacement lipomatosis (RRL) is a rare benign condition in which the renal parenchyma, especially the renal sinus, hilum, and peri-renal spaces are replaced by mature adipose tissue. ,, It is seen with calculus disease, renal tuberculosis, and infarction in 70% of cases. ,, Rare cases are idiopathic. We report our experience with an idiopathic case of RRL in a young patient along with the review of literature.
| > Case history|| |
A 30 year-old female patient presented with the complaint of pain in left lumbar region for the past 1 year. Pain was mild, dull, progressively increasing, and non-radiating. On examination, a non-tender, firm, ill-defined mass in the left renal region was palpated. There was no associated tuberculosis, hypertension, or diabetes mellitus. Urine examination and renal function tests were within normal limits. Clinically, left renal calculus was suspected. X-ray of kidney-ureter-bladder (KUB) region showed no calculi. Ultrasonography of KUB region revealed a left hypoplastic kidney. On intravenous pyelography, left kidney was not visualized. Dynamic renal dimercaptosuccinic acid (DMSA) scan revealed right kidney normal in size, shape, position, perfusion, concentration, and clearance of the dye. The left kidney was not visualized [Figure 1]. A left nephrectomy was performed for a left non-functioning kidney. A distorted left kidney was removed and was sent for histopathological examination. The specimen of kidney with perinephric fat measured 12 × 6 × 3 cm. On cut surface, the entire parenchyma was replaced by adipose tissue with extremely atrophied renal parenchyma and moderately dilated pelvi-calyceal system [Figure 2]. Microscopic examination revealed extensive infiltration of the renal parenchyma by lobules of mature adipose tissues. The compressed renal parenchyma at the periphery showed atrophy with sclerosed glomeruli, thyroidization of tubules, interstitial fibrosis, and thickened blood vessels. There was a clear demarcation between adipose tissue and renal parenchyma [Figure 3]. Inflammation was moderate comprising of lymphocytes, plasma cells, macrophages, and few neutrophils. The lining of pelvi-calyceal system was unremarkable. No xanthomatous change or neoplasm was observed. A thorough search of literature was made and a diagnosis of RRL was made. The patient remained asymptomatic after 6 months of follow-up.
|Figure 2: Gross photograph of kidney shows extensive replacement of renal tissue by mature adipose tissue on cut surface|
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|Figure 3: Microphotograph of kidney showing well-demarcated mature adipose tissue and atrophied renal parenchyma with thick-walled dilated tubules showing thyroidization, interstitial fibrosis, and inflammatory cells|
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| > Discussion|| |
RRL was first described by Kurtzmann in 1931 as reported by Peacock and Balle.  Renal sinus lipomatosis, replacement lipomatosis, and fibrolipomatosis of the kidney are the terms used for this condition and represent a spectrum of changes.  This spectrum is different from renal lipomas that are neoplastic, whereas this condition is thought to be a degenerative condition. , Renal sinus lipomatosis is the mildest form, occurs in sixth to seventh decade, associated with obesity, atherosclerosis, or exogenous steroids. , It is clinically insignificant but may cause mass effect on the intra-renal collecting system and produce obstruction.  At the other end of the spectrum is RRL in which the entire renal parenchyma is replaced with adipose tissue. In 70% cases it is associated with calculi, renal tuberculosis, and renal infarction. ,, Majority of the cases are unilateral and rare cases are idiopathic. , In our case, there was no predisposing factor in past or present, and patient was not obese, thus we labeled it as idiopathic.
In this case, the patient was young, which is in contrast to majority of cases that are reported in elderly, except one which is reported in second decade associated with posterior mediastinal lipomatosis. , Radiological investigations especially computed tomography scan and magnetic resonance imaging confirm the fatty infiltration of the kidney and its distribution in the renal sinus and peri-renal space.  Renal lipoma, angiomyolipoma, xanthogranulomatous pyelonephritis, and liposarcoma are the usual differential diagnosis on computed tomography scan and magnetic resonance imaging. , Ultrasonography is not very useful, as in our case.
Grossly, the kidney may be enlarged or small in size. The renal parenchyma is atrophied and may undergo hydronephrosis. , This feature helps to distinguish it from tumors of the kidney where the renal parenchyma is not atrophied. Microscopically, a renal lipoma with which RRL can be easily confused has characteristic features. A renal lipoma is a well circumscribed and encapsulated mass of mature adipose tissue. It is usually attached to some portion of the capsule and it dips well into the parenchyma. There is no associated pathology of glomeruli or tubules except in the area surrounding the compressing adipose tissue mass. In contradistinction, in RRL there is renal destruction. There is displacement of normal renal structures by the fat cells. All cases show infiltration by chronic inflammatory cells. 
Xanthogranulomatous pyelonephritis can be difficult to differentiate from RRL, as both entities show over-lapping clinico-etiologic features. In xanthogranulomatous lipomatosis there is destruction of the renal parenchyma, and lipid-laden macrophages (foamy macrophages) diffusely infiltrate the parenchyma in contrast to RRL where fat cells remain outside the atrophied renal parenchyma. 
Angiomyolipoma and liposarcoma can be easily differentiated from RRL due to the presence of smooth muscle fibers, thick-walled blood vessels in angiomyolipoma and lipoblasts in the liposarcoma. All these components are absent in RRL.
In conclusion, the important aspect of this case is rarity of the entity, younger age group and its idiopathic nature. It presents with poorly or non-functioning kidney. RRL can be confused with various adipose tissue tumors on radiology. Histologically, there is gradual replacement of the renal parenchyma with mature adipose tissue leading to end-stage renal disease. RRL may be missed due to inexperience. We hope more clinicians, radiologists, and pathologists are aware of this entity.
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[Figure 1], [Figure 2], [Figure 3]