AJR 2005; 184:1597-1599
© American Roentgen Ray Society
Nonneoplastic Hyperdense Enhancing Renal Mass: CT Findings and Pathologic Correlation
David J. Choi1,
Sridhar Shankar1,
Dariusz Stachurski2 and
Barbara F. Banner2
1 Department of Radiology, University of Massachusetts Medical Health Center,
Worcester, MA 01532.
2 Department of Pathology, University of Massachusetts Medical Health Center,
Worcester, MA 01532.
Received January 1, 2004;
accepted after revision August 12, 2004.
Address correspondence to Sridhar Shankar.
Introduction
Renal masses most commonly appear hypo- to isodense on unenhanced CT, and
enhancement after IV contrast administration typically prompts either close
follow-up or a pathologic diagnosis to exclude malignancy
[1]. Hyperattenuating renal
masses have been found to be hyperdense cysts
[2,
3], neoplasms
[2,
3], and angiomyolipomas with
minimal fat [4]. Enhancement of
a hyperattenuating mass excludes the diagnosis of a cyst. We describe, for the
first time to our knowledge, hyperdense, enhancing renal masses that
represented the end-stage changes of focal chronic tubulointerstitial
inflammation.
Case Report
A 41-year-old Brazilian man presented to the emergency department with
right flank pain. Physical examination revealed no fever or costovertebral
angle tenderness. Peripheral WBC count was 11 x 109 cells/L,
and the serum creatinine level was 1.4 mg/dL. Urinalysis showed 200 RBCs and 2
WBCs per high-power field. Urine culture revealed no growth.
CT scans (5-mm slice thickness) of the abdomen and pelvis were obtained on
an 8-MDCT scanner (LightSpeed Ultra, GE Healthcare) both before and after IV
contrast administration (iopamidol [Isovue-370, Bracco Diagnostics]). These
images showed two hyperattenuating lesions in the right renal parenchyma: the
first measuring 5.0 x 2.7 x 3.5 cm in the lower pole (Figs.
1A,
1B,
1C,
1D) and a second similar mass
measuring 3.5 x 1.8 x 3.0 cm in the interpolar region. Several
foci of lower attenuation, measuring 5 mm or less in diameter, were noted in
the hyperdense lesions. A 4-mm calculus was seen in a nondilated right renal
collecting system.
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Fig. 1C. —41-year-old man with right flank pain. CT images obtained 70
sec after IV contrast administration show enhancement of masses in interpolar
region (C) and lower pole (D) of right kidney. Subcentimeter
foci of lower attenuation are marked by arrows.
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Fig. 1D. —41-year-old man with right flank pain. CT images obtained 70
sec after IV contrast administration show enhancement of masses in interpolar
region (C) and lower pole (D) of right kidney. Subcentimeter
foci of lower attenuation are marked by arrows.
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The masses enhanced from approximately 75 H before IV contrast
administration to 130 H at 70 sec after IV contrast administration. No
contrast washout was noted at approximately 5 min after contrast injection.
Because the foci of lower attenuation measured no greater in size than the
slice collimation, reliable determination of their enhancement behavior was
not possible. The left kidney appeared unremarkable.
Approximately 1 year before presentation, the patient experienced a similar
episode of right flank pain that prompted an unenhanced CT examination of the
abdomen and pelvis at an outside institution. Those images showed a similar
appearance of the two masses. Three nonobstructing calculi measuring up to 5
mm in diameter were noted in the right renal collecting system at that
time.
Because the diagnosis of renal cell carcinoma could not be excluded, the
patient underwent right nephrectomy 2 weeks after the more recent CT scans
were obtained. A section of the gross specimen revealed a well-circumscribed,
firm, smooth, solid, yellow–pink mass in the lower pole containing
multiple 1- to 2-mm cysts filled with clear watery fluid. The mass involved
the cortex and calyx and extended to the capsule, but it did not penetrate the
capsule or invade perirenal fat. A second similar finely granular mass was
present in the interpolar region, and it also contained multiple fluid-filled
cysts, the largest measuring 5 mm. No necrosis or hemorrhage was seen. The
remainder of the cortex was red–brown with a well-defined
corticomedullary junction.
Microscopically, the masses comprised atrophic and cystically dilated
tubules, sclerotic glomeruli, and dystrophic calcifications enmeshed in a
sclerotic stroma (Figs. 1E and
1F). Trichrome staining of
histologic sections confirmed the presence of extensive background fibrosis
amid the tubules with cystic dilatation. A periodic-acid Schiff stain
highlighted residual atrophic and focally sclerotic glomeruli with intact
Bowman's membranes. These findings were consistent with the end-stage changes
of focal chronic tubulointerstitial inflammation and were not neoplastic in
nature.
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Fig. 1E. —41-year-old man with right flank pain. Photomicrograph of
histologic section from mass in right renal lower pole mass (left upper
portion of image) shows that it is well circumscribed by pseudocapsule and
bordered by normal renal cortex (right lower portion of image). Dystrophic
microcalcifications (arrows) are visible. Sections from the right
renal interpolar mass (not shown) were similar in appearance. (H and E,
x4)
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Fig. 1F. —41-year-old man with right flank pain. Photomicrograph of
histologic section from mass in right renal lower pole shows atrophic tubules
with cystic dilatation (arrowhead). Sections from the right renal
interpolar mass (not shown) were similar in appearance. (H and E,
x40)
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Discussion
The differential diagnosis for hyperattenuating renal masses includes
hyperdense cysts [2,
3], neoplasms
[2,
3], and angiomyolipomas with
minimal fat [4]. Findings such
as internal enhancement and heterogeneity, size
[5], and deenhancement
[6] have been proposed to
increase the diagnostic likelihood of neoplasm over hyperdense cyst. Such
factors, however, cannot be used to distinguish between benign and malignant
neoplasms—for example, oncocytoma and renal cell carcinoma. Macroscopic
fat is one of a few CT criteria that is widely accepted as increasing the
likelihood of a benign diagnosis, such as angiomyolipoma, for an enhancing
renal mass [7]. Sonography and
MRI also may be useful in decisions between close follow-up and histologic
evaluation of such lesions [1,
3].
The lesions described in our report most closely resemble the changes seen
during the end stages of chronic tubulointerstitial inflammation, which is a
nonspecific response to persistent tubular injury. As a result of this injury,
tubules may become atrophic, simplified, dilated, and filled with a
concentrated proteinaceous fluid. The low-attenuation subcentimeter foci
within the renal masses seen on CT may have represented cystic dilatation of
tubules. A whole field of such tubules resembles thyroid tissue in microscopic
sections and is referred to as "thyroidization." The fact that the
changes were so localized in this case suggests that the instigating
inflammatory process involved only some of the lobes or calices. Chronic
calyceal obstruction is the most likely cause for the lesions in the current
case. An expert in the pathology of renal masses at an outside institution,
John Eble at the Indiana University School of Medicine, concurred with this
interpretation. He noted that the changes were consistent with the
"upstream results of obstruction of the ducts of Bellini in the renal
papillae by calcifications, such as Randall's plaque" (Eble JN, personal
communication).
In the setting of focal obstruction, superimposed infection, as in focal
xanthogranulomatous pyelonephritis, may have been active in the distant past.
Although lipid-laden macrophages are present by definition in this disease,
they would not be expected long after the inflammation had resolved. Active
lesions of focal xanthogranulomatous pyelonephritis typically surround an
obstructed calyx and usually appear hypodense and enlarged on CT
[8]. Although RBCs and WBCs
were found in the patient's urine, the nephrectomy specimen, which was
obtained 4 weeks after the patient's latest presentation, did not show any
signs of recent infection on histopathologic examination. Neutrophil and
mononuclear cell counts in the renal lesions were normal. Selli et al.
[9] described a case of focal
xanthogranulomatous pyelonephritis that contained macroscopic bone metaplasia.
In contrast, the dystrophic calcifications described in our report were
microscopic and lacked any semblance of osseous tissue.
This report is the first description, to our knowledge, of an unusual CT
appearance of a recognized pathologic entity. We propose that an end-stage
diffusely microcalcified renal lesion caused by focal chronic
tubulointerstitial inflammation should be included in the differential
diagnosis for a hyperdense enhancing renal mass. These atypical CT findings,
however, are not pathognomonic for inflammatory lesions and cannot in
themselves substitute for histologic evaluation.
Acknowledgments
We thank Rhonda Yantiss, MD and Alan J. Davidson, MD for their helpful
comments.
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Introduction
Case Report
