DOI:10.2214/AJR.05.0866
AJR 2007; 189:W163-W165
© American Roentgen Ray Society
Fat-Fluid Levels in Renal Caliceal Cavities: A CT Sign of Lipolysis Due to Urine Extravasation After Kidney Rupture
Michaël Soussan1,
Isabelle Boulay-Coletta1,
Vincent Molinié2,
Walid Alamé3 and
Marc Zins1
1 Department of Radiology, Saint Joseph Hospital Foundation, 185 rue Raymond
Losserand, 75014 Paris, France.
2 Department of Pathology, Saint Joseph Hospital Foundation, Paris,
France.
3 Department of Urology, Saint Joseph Hospital Foundation, Paris, France.
Received May 23, 2005;
accepted after revision July 20, 2005.
Address correspondence to I. Boulay-Coletta
(iboulay{at}hopital-saint-joseph.org).
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Keywords: CT • genitourinary tract imaging • kidney • lipolysis
Introduction
Urine extravasation is a rare complication of urinary tract obstruction.
Urine leaks out of tears in the caliceal fornix and, more rarely, the renal
pelvis or ureter. In exceptional cases, urine leaks through perforations in
the renal wall. Lipolysis of perihilar tissues occurs within a few days of
urine extravasation [1]. We
describe caliceal fat-fluid levels visualized on CT in a patient who had
chronic obstructive pyelonephritis complicated by extensive kidney rupture
with extravasation of infected urine. We suggest that urine-induced lysis of
perirenal fat may have caused this CT finding. To our knowledge, this is the
first report of fat-fluid levels in renal calices.
Case Report
A 57-year-old man was admitted to our emergency department with a 2-week
history of left flank pain, malaise, fever (38.1°C), asthenia, and
anorexia. He had a history of untreated type 2 diabetes. Cutaneous erythema
over the left lumbar area and hemodynamic instability were found at physical
examination. Helical CT (Light-Speed Pro 16, GE Healthcare) of the abdomen and
pelvis was performed immediately with and without iodinated contrast material
and delayed scanning. An 8-mm stone obstructing the distal portion of the left
ureter was seen, as were diffuse pelvicaliceal dilatation and extensive
perirenal and pararenal fluid collections. The left kidney was diffusely
enlarged (length, 15 cm), and an extensive parenchymal tear was seen in the
upper pole (Figs. 1A and
1B). Fat-fluid levels were
visible in most of the dilated calices and in the pelvis. Density was -100 H
for the top component and 10 H for the bottom component
(Fig. 1C). A fat-fluid level
was also seen in the bladder (Fig.
1D). Enhancement was less marked in the left than the right
kidney, and excretion was asymmetric.
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Fig. 1A —57-year-old man with left flank pain, malaise, and fever.
Axial contrast-enhanced CT scan through kidneys shows parenchymal rupture of
left kidney with perirenal collection and fatlike attenuation
(arrowhead) in superior calix.
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Fig. 1B —57-year-old man with left flank pain, malaise, and fever.
Coronal reformatted CT scan shows extensive tear (arrow) in left
renal parenchyma, large heterogeneous perirenal collection, and low fatlike
attenuation (arrowhead) in superior calices.
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Fig. 1D —57-year-old man with left flank pain, malaise, and fever.
Axial contrast-enhanced CT scan through renal pelvis shows impacted stone
(arrowhead) in left ureter and fat-fluid level (arrows) in
bladder.
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Blood test abnormalities included leukocytosis (WBC count,
22,000/mm3) with predominance of neutrophils
(18,000/mm3), C-reactive protein elevation (312 mg/L),
hyperglycemia (17.8 mmol/L), and hyponatremia (123 mmol/L). The hemoglobin
concentration was 10.3 g/dL, and the hematocrit was 27%. The serum creatinine
concentration was normal. Urine and blood culture results were positive for
ß-hemolytic streptococci. Although the urine was turbid and orange to the
naked eye, test results were negative for cholesterol and triglycerides.
IV antibiotics were given, a ureteral catheter was inserted, and 1 L of pus
was drained surgically from the perirenal region. The left kidney showed no
evidence of function and was removed surgically 2 weeks later. The renal
calices were dilated and filled with pus. Histologic examination of the kidney
showed not only chronic tubulointerstitial pyelonephritis with
lymphoplasmacytic infiltrates but also foci of acute pyelonephritis with
neutrophilic infiltrates. There was no necrosis of the renal fat sinus. Within
the perirenal tissue, foci of lipolysis with marked inflammation and granuloma
formation were seen. The granuloma was composed of foamy macrophages and of
neutrophilic infiltrates containing multinucleate giant cells and lymphocytes
(Fig. 1E). Ulcers without
perforation were visible in the pelvicaliceal urothelium, and necrotic fatty
tissue was found in the caliceal lumens
(Fig. 1F). There was no
histologic evidence of xanthogranulomatous pyelonephritis (XGP).
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Fig. 1E —57-year-old man with left flank pain, malaise, and fever.
Photomicrograph of histologic specimen of perirenal tissue shows fat-cell
necrosis with severe inflammation and granulomatous lipolysis. (H and E,
x200)
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Discussion
The incidence of spontaneous extravasation of urine related to ureteral
stone obstruction has been estimated at 4% in patients undergoing excretory
urography [2]. Urine
extravasation occurs when elevation of pressure in the renal pelvis causes
urine to flow in the retrograde direction through the interstitial lymphatic
vessels. This reversal of flow tends to lower renal pelvic pressure. Increased
pressure in normal renal parenchyma causes microscopic tears in the fornices
of the minor calices, which are the weakest points, and these tears
subsequently extend to the renal sinus. Urine leaks into the renal sinus then
flows in the retrograde direction into the veins and lymphatic vessels. When
the amount of urine exceeds reabsorption, urine can leak around the renal
hilus into the perirenal fat tissue and occasionally downward along the ureter
or psoas muscle, where a urinoma develops
[3]. In rare instances, urine
leaks out of a breach in the renal pelvis caused by necrosis at a site of
pressure from an impacted pelvic stone.
Rupture of the renal parenchyma is uncommon but has been reported to occur
after renal trauma, uroradiologic procedures, and open renal surgery. In
patients with ureteral calculus, spontaneous rupture of the renal parenchyma
is exceedingly rare. The cases reported to date have occurred in association
with renal parenchymal disease such as renal tumor, periarteritis nodosa,
chronic pyelonephritis, pyonephrosis, and abscess
[4]. Spontaneous rupture of the
kidney can cause retroperitoneal hematoma and, when the urine is infected,
retroperitoneal abscess and peritonitis
[5,
6].
When urine leaks into the perirenal fat, macroscopic edema promptly
develops [7]. The first
microscopic urine-induced abnormality is lipolysis, which is seen as fat
tissue disruption with infiltration by foamy macrophages (xanthoma cells),
multinucleate giant cells, and lymphocytes. Later, fibrous tissue is
substituted for the perihilar and perirenal fat. The cause of urine-induced
lipolysis is unknown. Urine contains no substances capable of inducing lipase
activation. Adipocyte membrane disruption may be related to changes in osmotic
pressure [1].
Our patient had a 2-week history of ureteral stone obstruction with
infection. The extensive tear in the renal parenchyma can be ascribed to
pressure elevation and to parenchymal damage produced by the chronic and acute
renal infection. Abnormal fragility of the renal parenchyma is a key factor in
parenchymal rupture. The massive leakage of pus and urine into the perirenal
space in our patient may explain the severe malaise. CT showed a wide
communication between the renal cavities and perirenal space. The large amount
of urine and pus in the perirenal region caused fat necrosis, as found at
histologic examination. No perforation of pelvicaliceal urothelium or
lipolysis was found in the renal fat sinus at pathologic examination. For this
reason, we hypothesize that the fat-fluid levels in the renal cavities and
bladder were more likely due to lipolysis of perirenal fat followed by
penetration of fat components into the renal calices than to fat necrosis
coming from the renal fat sinus. We are not aware of previous reports
describing fat-fluid levels in the renal cavities of a patient with renal
colic complicated by urinary tract infection. A plausible explanation is that
extensive renal rupture is exceedingly rare in this situation.
Ureteral obstruction with urine extravasation and lipolysis must be
differentiated from XGP. Although the clinical manifestations may be similar,
at pathologic examination XGP is defined as rounded masses composed of an
infiltrative process with accumulation of lipid-laden macrophages intermixed
with a variety of inflammatory cells in the renal parenchyma. At CT, however,
evidence of XGP is diffuse kidney enlargement with replacement of the
parenchyma by multiple low-attenuation (10-15 H) rounded masses corresponding
either to dilated calices filled with pus and xanthomatous tissue or to foci
of parenchymal destruction [8].
In contrast, in our patient, CT and macroscopic examination showed no mass,
and microscopic examination did not reveal accumulation of lipid-laden
macrophages in the renal parenchyma. In this case, perirenal fat lipolysis
with fat-fluid levels in the renal cavities was clearly a different entity
from XGP. This case of CT visualization of fat-fluid levels in the
pelvicaliceal cavities of the kidney constitutes, to our knowledge, the first
reported evidence of perirenal lipolysis due to urine extravasation through a
large renal parenchymal tear.
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Introduction
Case Report
