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Case Replacement Lipomatosis of the Kidney Radiology

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									Stephen Karasick, MD
Richard J. Wechsler, MD




Case 23: Replacement Lipomatosis
of the Kidney1
HISTORY                                                                 kidney with preservation of its reniform shape. There was a
                                                                        highly echogenic appearance to the renal sinus consistent with
A 49-year-old man underwent computed tomography (CT)                    fat that extended to the periphery and occupied most of the
prior to possible bilateral nephrectomy. He had a history of            renal tissue. A 1.5-cm stone was present in the lower pole of the
end-stage renal disease secondary to a neurogenic bladder with          left kidney (Fig 5).
chronic reflux nephropathy and chronic pyelonephritis. The
patient also had spina bifida, hypertension, hepatitis B, atrial
fibrillation, hypothyroidism, and degenerative joint disease.           DISCUSSION
He had been receiving hemodialysis for 6 years and has a
ureteroileostomy.                                                       Replacement lipomatosis of the kidney, also known as replace-
   A digital abdominal radiograph (Fig 1) was obtained prior to         ment fibrolipomatosis, is an advanced form of renal sinus
abdominal pelvic CT. CT scans through the top of the kidneys            lipomatosis that usually occurs unilaterally. A varying amount
at the level of the celiac axis (Fig 2) and through the lower pole      of fat and fibrous tissue is always present within the renal sinus,
of the left kidney (Fig 3) are shown.                                   which becomes more prominent with aging, obesity, and use of
                                                                        exogenous steroids. Replacement fibrolipomatosis represents
IMAGING FINDINGS                                                        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 dis-
A digital abdominal radiograph (Fig 1) obtained prior to CT
                                                                        ease associated with inflammatory changes is found in more
showed markedly enlarged kidneys with multiple renal calculi.
                                                                        than 70% of cases (8). Clinical symptoms, including urinary
A large, smoothly lobulated 9         4-cm calculus was noted
                                                                        tract infections, fever, and flank pain, usually result from the
overlying the right renal pelvis and ureter. A transverse CT scan
                                                                        associated inflammatory and calculous disease (2).
through the upper kidneys (Fig 2) revealed extreme parenchy-
                                                                           Pathologically, the kidney usually is enlarged and has a gross
mal atrophy with marked fatty proliferation within the renal
                                                                        fibrofatty appearance. The renal cortex is extremely atrophied,
sinus, hilus, and perinephric space. A transverse CT scan
                                                                        with varying degrees of hydronephrosis or pyonephrosis, as
through the lower pole of the left kidney (Fig 3) revealed left
                                                                        well as having acute and chronic pyelonephritic changes. The
renal calculi and a large right staghorn calculus. An ultrasono-
                                                                        reniform shape of the kidney is maintained. There is marked
graphic (US) scan, obtained in the left kidney (Fig 4) several
                                                                        proliferation of hyperplastic fat in the renal sinus, with ex-
months before the CT scans, revealed enlargement of the
                                                                        tremely large fat cells that do not permeate the renal paren-
                                                                        chyma 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.
  Index terms:                                                             The abdominal radiograph characteristically demonstrated a
  Diagnosis Please                                                      staghorn calculus with an enlarged renal outline (Fig 1).
  Kidney, calculi, 81.811                                               Excretory urography demonstrated a poorly functioning or
  Kidney, CT, 81.1211                                                   nonfunctioning kidney. At US, there was expansion of the
  Kidney, US, 81.1298                                                   hyperechoic mass that represented lipomatous tissue in the
  Lipoma and lipomatosis, 81.3119
                                                                        central sinus (Fig 4). A central high-intensity echo with acous-
  Nephritis, 81.2125, 81.213
                                                                        tic shadowing represented the staghorn or other calculus (Fig
  Radiology 2000; 215:754–756                                           5). It may be difficult to see the hypoechoic rim of the residual
                                                                        parenchyma (8). Although US may show highly suggestive
  1
                                                                        findings, CT is the most accurate method of demonstrating the
    From the Department of Radiology, Thomas Jefferson University
  Hospital, 111 S 11th St, Ste 3390, Philadelphia, PA 19107. Received   distinctive features of replacement lipomatosis. The staghorn
  December 21, 1998; revision requested February 9, 1999; revision      calculus and the atrophied renal parenchyma were depicted
  received March 3; accepted July 30. Address correspondence to S.K.    easily (Figs 2, 3). The abundant fatty tissue centrally has the
  (e-mail: Stephen.Karasick@mail.tju.edu).                              characteristic attenuation of fat (5–10). The characteristic distri-
      RSNA, 2000                                                        bution of fat within the renal sinus and perinephric space is
                                                                        unique to replacement lipomatosis. If surgery is indicated, CT

754
                                                                        Figure 3. Transverse contrast-enhanced abdominal CT scan ob-
                                                                        tained through the lower pole of the left kidney reveals scattered left
                                                                        renal calculi and a large right staghorn calculus (*).




Figure 1. Anteroposterior digital abdominal radiograph obtained
prior to abdominal CT reveals enlarged kidneys with scattered calculi
(arrows) and right staghorn calculus (*).




                                                                                    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.




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               Figure 5. Transverse US scan obtained through
attenuation adjacent to the right kidney represent exophytic renal                  the lower pole of the left kidney revels a 1.5-cm
cysts.                                                                              stone (arrow) with shadowing beneath.



can be valuable in the preoperative planning by demonstrating           lipomatosis in which the fat cells remain outside of the
the absence or presence of abscess and fistula formation.               atrophied renal parenchyma. The features at US and CT are,
   The major differential diagnosis in the presence of long-            therefore, different. At US, with xanthogranulomatous pyelone-
standing inflammation and calculous obstruction is xantho-              phritis, there are hypoechoic areas that represent purulent
granulomatous pyelonephritis. Lipid-laden macrophages actu-             material, as well as medium-amplitude echoes that correspond
ally infiltrate the renal parenchyma in contrast to replacement         to the fibrofatty and/or necrotic debris (8). CT shows hydrone-

Volume 215 • Number 3                                                                            Replacement Lipomatosis of the Kidney • 755
phrosis or pyonephrosis along with xanthogranulomatous                   4.   Hurwitz RS, Benjamin JA, Cooper JF. Excessive proliferation of
tissue, which typically has attenuation values close to that of               peripelvic fat of the kidney. Urology 1978; 11:448–456.
                                                                         5.   Honda H, McGuire CW, Barloon TJ, Hashimoto K. Replacement
water ( 15 to 15 HU).                                                         lipomatosis of the kidney: CT features. J Comput Assist Tomogr
   Xanthogranulomatous pyelonephritis and replacement fibro-                  1990; 14:229–231.
lipomatosis may coexist (11). Replacement fibrolipomatosis               6.   Kullendorff B, Nyman V, Aspelin P. Computed tomography in
may be tumefactive, in which case other focal fatty lesions such              renal replacement lipomatosis. Acta Radiol 1987; 28:447–450.
                                                                         7.   Thierman D, Haaga JR, Anton P, LiPuma JP. Renal replacement
as lipoma, angiomyolipoma, and liposarcoma must be consid-
                                                                              lipomatosis. J Comput Assist Tomogr 1983; 7:341–343.
ered. The absence of parenchymal atrophy and staghorn calcu-             8.   Subramanyam BR, Bosniak MA, Horii SC, Megibow AJ, Balthazar
lus are additional clues for excluding these entities (6).                    EJ. Replacement lipomatosis of the kidney: diagnosis by computed
                                                                              tomography and sonography. Radiology 1983; 148:791–792.
                                                                         9.   Nicholson DA. Case report: replacement lipomatosis of the kid-
References                                                                    ney—unusual CT features. Clin Radiol 1992; 45:42–43.
 1. Young HH. Lipomatosis or destructive fat replacement of the renal   10.   Amis ES, Cronan JJ. The renal sinus: an imaging review and
     cortex. J Urol 1933; 29:631–644.                                         proposed nomenclature for sinus cysts. J Urol 1988; 139:1151–
 2. Gildenhorn HL. Renal replacement lipomatosis: review and case             1159.
     report. JAMA 1962; 181:994–996.                                    11.   Acunas B, Acunas G, Rozanes I, Buyokbabani N, Gokmen E.
 3. Ambos MA, Bosniak MA, Gordon R, Madayag MA. Replacement                   Coexistent xanthogranulomatous pyelonephritis and massive re-
     lipomatosis of the kidney. AJR Am J Roentgenol 1978; 130:1087–           placement lipomatosis of the kidney: CT diagnosis. Urol Radiol
     1091.                                                                    1990; 12:88–90.


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                                       Julio Mendez-Uriburu, Tucuman, Argentina
Yasutaka Baba, Kagoshima, Japan                                         Manabu Minami, MD, Tokyo, Japan
Edward L. Baker, MD, San Francisco, Calif                               Robert Mindelzun, MD, Palo Alto, Calif
Ken Baliga, Rockford, Ill                                               Sergio J. Moguillansky, MD, Cipolletti, Rio Negro, Argentina
Marc P. Banner, MD, Voorhees, NJ                                        Dr. Miguel Eduardo Nazar, Capital Federal, Argentina
Etta Barracciu, Cagliari, Italy                                         Carlo L. E. Petralli, Switzerland
Giuseppe Brancatelli, MD, Palermo, Italy                                James Ravenel, MD, Syracuse, NY
Eric L. Bressler, Minnetonka, Minn                                      Enrique Remartinez Escobar, MD, Melilla, Spain
Christophe J. Chagnaud, MD, Marseille, France                                                          ˆ
                                                                        Pierre-Jean Sauvage, MD, Macon, France
Kemal Demir, MD, Istanbul, Turkey                                       Matt Shapiro, MD, Lowell, Mass
Olivier Dourthe, MD, Sophia Antipolis, France                           Taro Shimono, MD, Kyoto, Japan
Seyed A. Emamian, MD, PhD, Washington, DC                               Paolo Siotto, MD, Cagliari, Italy
Howard T. Heller, MD, Garden City, NY                                   Toshiaki Takeda, Tokyo, Japan
Ryuji Katada, MD, Sapporo, Japan                                        Douglas L. Teich, MD, Brookline, Mass
Richard A. Leder, MD, Durham, NC                                        D. Dean Thornton, MD, Kirkwood, Mo
N. B. S. Mani, MD, Chandigarh, India                                    Kay Vilanova, MD, Girona, Spain
                       ´
Antonio Medina Benıtez, Granada, Spain                                  Joe Yut, Olathe, Kan




756 • Radiology • June 2000                                                                                            Karasick and Wechsler

								
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