(Radiology. 2000;215:754-756.)
© RSNA, 2000
Case 23: Replacement Lipomatosis of the Kidney1
Stephen Karasick, MD and
Richard J. Wechsler, MD
1 From the Department of Radiology, Thomas Jefferson University Hospital, 111 S 11th St, Ste 3390, Philadelphia, PA 19107. Received December 21, 1998; revision requested February 9, 1999;
revision received March 3; accepted July 30. Address correspondence to S.K. (e-mail: Stephen.Karasick@mail.tju.edu).
Index terms: Diagnosis Please • Kidney, calculi, 81.811 • Kidney, CT, 81.1211 • Kidney, US, 81.1298 • Lipoma and lipomatosis, 81.3119 • Nephritis, 81.2125, 81.213
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HISTORY
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A 49-year-old man underwent computed tomography (CT) prior to possible bilateral nephrectomy. He had a history of end-stage renal disease secondary to a neurogenic bladder with chronic reflux nephropathy and chronic pyelonephritis. The patient also had spina bifida, hypertension, hepatitis B, atrial fibrillation, hypothyroidism, and degenerative joint disease. He had been receiving hemodialysis for 6 years and has a ureteroileostomy.
A digital abdominal radiograph (Fig 1) was obtained prior to abdominal pelvic CT. CT scans through the top of the kidneys at the level of the celiac axis (Fig 2) and through the lower pole of the left kidney (Fig 3) are shown.
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Figure 2. Transverse contrast material-enhanced abdominal CT scan obtained through the upper kidneys reveals extreme renal parenchymal atrophy with only a thin rim (arrows) of renal cortex remaining. The renal sinus and hilus have been replaced with fat that extends into the perinephric space. The rounded masses of soft-tissue attenuation adjacent to the right kidney represent exophytic renal cysts.
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Figure 3. Transverse contrast-enhanced abdominal CT scan obtained through the lower pole of the left kidney reveals scattered left renal calculi and a large right staghorn calculus (*).
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IMAGING FINDINGS
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A digital abdominal radiograph (Fig 1) obtained prior to CT showed markedly enlarged kidneys with multiple renal calculi. A large, smoothly lobulated 9 x 4-cm calculus was noted overlying the right renal pelvis and ureter. A transverse CT scan through the upper kidneys (Fig 2) revealed extreme parenchymal atrophy with marked fatty proliferation within the renal sinus, hilus, and perinephric space. A transverse CT scan through the lower pole of the left kidney (Fig 3) revealed left renal calculi and a large right staghorn calculus. An ultrasonographic (US) scan, obtained in the left kidney (Fig 4) several months before the CT scans, revealed enlargement of the kidney with preservation of its reniform shape. There was a highly echogenic appearance to the renal sinus consistent with fat that extended to the periphery and occupied most of the renal tissue. A 1.5-cm stone was present in the lower pole of the left kidney (Fig 5).
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Figure 4. Transverse US scan obtained through the upper pole of the left kidney reveals the highly echogenic appearance of the renal sinus (calipers) with fat that extends to the periphery and replaces most of the renal tissue. The kidney, however, has preserved its reniform shape.
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DISCUSSION
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Replacement lipomatosis of the kidney, also known as replacement fibrolipomatosis, is an advanced form of renal sinus lipomatosis that usually occurs unilaterally. A varying amount of fat and fibrous tissue is always present within the renal sinus, which becomes more prominent with aging, obesity, and use of exogenous steroids. Replacement fibrolipomatosis represents the extreme form of renal sinus lipomatosis in which infection, long-term hydronephrosis, and calculi are associated with severe renal parenchymal atrophy (1–8). Renal calculous disease associated with inflammatory changes is found in more than 70% of cases (8). Clinical symptoms, including urinary tract infections, fever, and flank pain, usually result from the associated inflammatory and calculous disease (2).
Pathologically, the kidney usually is enlarged and has a gross fibrofatty appearance. The renal cortex is extremely atrophied, with varying degrees of hydronephrosis or pyonephrosis, as well as having acute and chronic pyelonephritic changes. The reniform shape of the kidney is maintained. There is marked proliferation of hyperplastic fat in the renal sinus, with extremely large fat cells that do not permeate the renal parenchyma but merely develop adjacent to it as it atrophies (3,4). This process is distinct from that seen with lipomas, which are found within the parenchyma.
The abdominal radiograph characteristically demonstrated a staghorn calculus with an enlarged renal outline (Fig 1). Excretory urography demonstrated a poorly functioning or nonfunctioning kidney. At US, there was expansion of the hyperechoic mass that represented lipomatous tissue in the central sinus (Fig 4). A central high-intensity echo with acoustic shadowing represented the staghorn or other calculus (Fig 5). It may be difficult to see the hypoechoic rim of the residual parenchyma (8). Although US may show highly suggestive findings, CT is the most accurate method of demonstrating the distinctive features of replacement lipomatosis. The staghorn calculus and the atrophied renal parenchyma were depicted easily (Figs 2, 3). The abundant fatty tissue centrally has the characteristic attenuation of fat (5–10). The characteristic distribution of fat within the renal sinus and perinephric space is unique to replacement lipomatosis. If surgery is indicated, CT can be valuable in the preoperative planning by demonstrating the absence or presence of abscess and fistula formation.
The major differential diagnosis in the presence of long-standing inflammation and calculous obstruction is xanthogranulomatous pyelonephritis. Lipid-laden macrophages actually infiltrate the renal parenchyma in contrast to replacement lipomatosis in which the fat cells remain outside of the atrophied renal parenchyma. The features at US and CT are, therefore, different. At US, with xanthogranulomatous pyelonephritis, there are hypoechoic areas that represent purulent material, as well as medium-amplitude echoes that correspond to the fibrofatty and/or necrotic debris (8). CT shows hydronephrosis or pyonephrosis along with xanthogranulomatous tissue, which typically has attenuation values close to that of water (-15 to +15 HU).
Xanthogranulomatous pyelonephritis and replacement fibrolipomatosis may coexist (11). Replacement fibrolipomatosis may be tumefactive, in which case other focal fatty lesions such as lipoma, angiomyolipoma, and liposarcoma must be considered. The absence of parenchymal atrophy and staghorn calculus are additional clues for excluding these entities (6).
Our congratulations to the 34 individuals who submitted the most likely diagnosis (replacement lipomatosis of the kidney) for Diagnosis Please, Case 23. The names and locations of the individuals, as submitted, are as follows:
- Marco A. Amendola, MD, Miami, Fla
- Yasutaka Baba, Kagoshima, Japan
- Edward L. Baker, MD, San Francisco, Calif
- Ken Baliga, Rockford, Ill
- Marc P. Banner, MD, Voorhees, NJ
- Etta Barracciu, Cagliari, Italy
- Giuseppe Brancatelli, MD, Palermo, Italy
- Eric L. Bressler, Minnetonka, Minn
- Christophe J. Chagnaud, MD, Marseille, France
- Kemal Demir, MD, Istanbul, Turkey
- Olivier Dourthe, MD, Sophia Antipolis, France
- Seyed A. Emamian, MD, PhD, Washington, DC
- Howard T. Heller, MD, Garden City, NY
- Ryuji Katada, MD, Sapporo, Japan
- Richard A. Leder, MD, Durham, NC
- N. B. S. Mani, MD, Chandigarh, India
- Antonio Medina Benítez, Granada, Spain
- Julio Mendez-Uriburu, Tucuman, Argentina
- Manabu Minami, MD, Tokyo, Japan
- Robert Mindelzun, MD, Palo Alto, Calif
- Sergio J. Moguillansky, MD, Cipolletti, Rio Negro, Argentina
- Dr. Miguel Eduardo Nazar, Capital Federal, Argentina
- Carlo L. E. Petralli, Switzerland
- James Ravenel, MD, Syracuse, NY
- Enrique Remartinez Escobar, MD, Melilla, Spain
- Pierre-Jean Sauvage, MD, Mâcon, France
- Matt Shapiro, MD, Lowell, Mass
- Taro Shimono, MD, Kyoto, Japan
- Paolo Siotto, MD, Cagliari, Italy
- Toshiaki Takeda, Tokyo, Japan
- Douglas L. Teich, MD, Brookline, Mass
- D. Dean Thornton, MD, Kirkwood, Mo
- Kay Vilanova, MD, Girona, Spain
- Joe Yut, Olathe, Kan
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References
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Gildenhorn HL. Renal replacement lipomatosis: review and case report. JAMA 1962; 181:994-996.
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Ambos MA, Bosniak MA, Gordon R, Madayag MA. Replacement lipomatosis of the kidney. AJR Am J Roentgenol 1978; 130:1087-1091.[Abstract]
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Hurwitz RS, Benjamin JA, Cooper JF. Excessive proliferation of peripelvic fat of the kidney. Urology 1978; 11:448-456.[Medline]
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Honda H, McGuire CW, Barloon TJ, Hashimoto K. Replacement lipomatosis of the kidney: CT features. J Comput Assist Tomogr 1990; 14:229-231.[Medline]
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Kullendorff B, Nyman V, Aspelin P. Computed tomography in renal replacement lipomatosis. Acta Radiol 1987; 28:447-450.[Medline]
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Thierman D, Haaga JR, Anton P, LiPuma JP. Renal replacement lipomatosis. J Comput Assist Tomogr 1983; 7:341-343.[Medline]
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Subramanyam BR, Bosniak MA, Horii SC, Megibow AJ, Balthazar EJ. Replacement lipomatosis of the kidney: diagnosis by computed tomography and sonography. Radiology 1983; 148:791-792.[Abstract/Free Full Text]
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Nicholson DA. Case report: replacement lipomatosis of the kidney—unusual CT features. Clin Radiol 1992; 45:42-43.[Medline]
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Amis ES, Cronan JJ. The renal sinus: an imaging review and proposed nomenclature for sinus cysts. J Urol 1988; 139:1151-1159.[Medline]
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Acunas B, Acunas G, Rozanes I, Buyokbabani N, Gokmen E. Coexistent xanthogranulomatous pyelonephritis and massive replacement lipomatosis of the kidney: CT diagnosis. Urol Radiol 1990; 12:88-90.[Medline]
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TOP
HISTORY
IMAGING FINDINGS
