Case Report
Pseudo-tumoral xanthogranulomatous pyelonephritis after excessive ESWL for renal stone
Dr. Sallami Sataa Department of Urology La Rabta Hospital - University Tunis, Tunisia sataa_sallami@yahoo.fr
Co-authors: Ben Rhouma Sami, Tanguour Monia, et al. Dept of Urology, La Rabta Hospital – University, Tunis, Tunisia
Xanthogranulomatous pyelonephritis (XGP) is a rare
and aggressive form of chronic pyelonephritis, which
is usually caused by calculous obstructive uropathy.
We present the case of a man with a history of
extracorporeal shock wave lithotripsy (ESWL) for
right renal stones, who was admitted with right loin
pain.
Abdominal ultrasound and computed tomography of
the abdomen were suggestive of renal tumour. He
underwent a radical nephrectomy and pathological
studies found a pseudo-tumoural XGP. Our case
suggests that the diagnosis of XPN should be
considered in patients with a renal tumour and
history of ESWL for renal stones.
Aggressive bacterial infection
XGP is an unusual and aggressive form of chronic
bacterial infection of the renal parenchyma,
pathologically characterised by accumulation of
lipid-laden foamy macrophages and destruction of
the renal parenchyma, often associated with calculi,
urinary tract infection and obstruction (1).
It may, rarely, occur as a renal tumour syndrome,
simulating mainly a renal cell carcinoma. The
diagnosis is often difficult (2,3) even with surgical
findings and, frequently, presents a histological
surprise. We report a case secondary to an excessive
ESWL for renal stone.
Case report
A 62-year-old man presented with a single episode of
gross hematuria and right-sided low lumbar pain.
Micturation was normal. There was no history of
weight loss, anorexia or progressive fatigue. The
patient denied any history of recurrent urinary tract
infections but more than 13 sessions ESWL for a right
renal stone were previously performed a year ago.
On admission, the physical examination revealed a
healthy appearing individual. Abdominal examination
showed a soft and lax abdomen with a ballotable
tender mass having ill-defined margins in the right
lumbar region.
Laboratory tests showed a normal white blood count
and erythrocyte sedimentation rate of 47 mm in the
first hour. All other blood tests were within normal
limits especially serum creatinine. Urine cultures did
not reveal any growth of common organisms or
acid-fast bacilli. The chest X-ray was normal.
Abdominal ultrasonography revealed a hypoechoic
solid mass in the right kidney with multiple renal
stones (Fig. 1). The left kidney and ureter were
normal.
On plain CT (Fig. 2) the mass was slightly hypodense
compared to the renal parenchyma and containing
calcifications. There was mild and heterogeneous
enhancement after intravenous injection of iodinated
contrast medium. The lesion extended to the perirenal
fat tissue. The diagnosis of focal xanthogranulomatous
pyelonephritis was suspected, although a tumoural
process could not be excluded with certainty. Thus, a
radical nephrectomy was decided.
Routine nephrectomy
Through a left lumbar incision routine nephrectomy
was performed. The resected right kidney showed an
adherent capsule and a granular cortex covered with
purulent excudates. Infiltration of the neighboring
psoas muscle was also identified.
On cut section multiple attached yellowish masses were
found in the renal parenchyma including the renal
capsule of the lower and lateral part of the kidney.
There were no suppurative lesions in the kidney.
Histopathological diagnosis was xanthogranuloma of
the kidney (Fig.3). Follow-up six months later was
unremarkable.
Discussion
XGP is an infrequent, severe, chronic bacterial infection
of the kidneys characterised by the destruction of the
renal parenchyma and the presence of granulomas,
abscesses and foam cells (2,3). The disease has been
reported at all ages, but predominantly affects females,
in the fifth through the sixth decades of life. It is
usually unilateral but rare cases of bilateral
involvement have been reported (1,4).
Two forms of presentation of XGP have been reported.
(3, 5). Diffuse XGP which is more frequent and is
characterised by an enlarged non-functioning kidney
associated with calculus. The very unusual focal XGP
is said to commonly affect more children and, due to
its pseudotumoral appearance, can simulate primary
renal neoplasm (5). We report a case of focal XGP in a
poor-functioning kidney secondary to excessive ESWL
for renal stones.
XGP is frequently associated with nephrolithiasis (up
to 80% of cases)(6) urinary infections produced by
Escherichia coli and Proteus mirabilis (5), or urinary
tract abnormalities (7). Yet, XGP may occur without
clear predisposing uropathy nor a history of present
or previous urinary infection (5). XGP is likely to be
one kind of immunologic mediated granuloma
following blunt renal trauma as reported by Chen et
al. and as reported in our case (8).
Clinically XGP presents with unspecified findings. The
most frequent symptoms were flank pain and fever
(5). Some hematological and biochemical parameters
may be altered: anemia and leucocytosis (5).
Urography schows an enlarged non-functioning
kidney with an obstructing or staghorn calculus. In
focal XGP, it shows a non-specific mass of variable
character but they may reveal calculosis,
hydronephrosis or renal mass, but these findings are
non-specific (7). Ultrasonography may show a
hypoechoic mass and minimal perirenal involvement
with thickening of posterior Gerota's fascia (9).
The typical CT appearance of focal XGP is that off a
well-defined heterogeneous soft tissue mass
containing areas of low attenuation. The presence of
fat density areas within the mass has been
occasionally described and it is related to the
presence of lipid-laden macrophages in XGP (5), as
well as calcifications within the mass, may also be
observed (10).
Fig. 2: CT scan with intravenous contrast. A low-density mass in
the region of the right renal hilus (*) and lower pole surrounds
the proximal ureter.
In our case, multiple small low attenuation areas
within the renal mass were seen (Fig. la), and
probably they were related to necrosis. The disease is
frequently extended to the perirenal space. Pararenal
infiltration and involvement of neighbouring organs
has also been described (10).
CT, which is considered the imaging modality of
choice (10), reveals the lesion but differential
diagnosis from hydro- or pyonephrosis, abcess
malakoplakia, lymphoma, congenital malformation
such as focal renal dysplasia (6,11) and especially
renal neoplasms is sometimes difficult.
There are only a few case reports concerning MRI
features in XGP (5). MRI aspect of focal XGP has been
reported with signal intensity higher than fluid on
Tl-weighted and lower than fluid on T2-weighted
images suggesting an atypical cystic neoplasm (5). In
other cases, it presented as a mass with intermediate
heterogeneous signal intensity on Tl weighted
sequence; central areas of hypointense signal on
T2-weighted (12).
The hyperintense signal should be related to the
inflammatory tissue and the hypointense
areas can be due to fat-laden foam cells in XGP (5).
MRI remains inferior to CT in demonstrating
calcifications (12). In our patient MRI exam was not
performed.
Both CT and MRI are equally suited to display the
morphology of this uncommon renal disease. For
Ramboer and all the diagnosis of focal
xanthogranulomatous pyelonephritis is suggested in
wedge- shaped lesion aspect on CT with the absence
of hyperintensity on fast T2-weighted sequences (3,6).
Computed tomography seems to be sufficient for XPN
imaging evaluation, while MRI is not recommended
on a routine basis, since no additional valuable
information is yielded (12).
Some authors have reported cases of pseudoneoplastic
xanthogranulomatous pyelonephritis diagnosed by a
renal CT guided biopsy. Furthermore, total renal
recovery was achieved by antibiotic treatment alone
avoiding surgical management (11). Needle aspiration
biopsy could have been helpful for the diagnosis.
However, because XGP may occur simultaneously with
a transitional cell carcinoma or renal cell carcinoma,
the idea was rejected in our case (6).
Figure. 3: Polymorphous infiltrate made of numerous foamy histiocytes (arrow), lymphocytes,
neutrophils and plasma cells. Hex400
Features that have been considered to be characteristic
for xanthogranulomatous pyelonephritis include the
renal enlargement, strands in the perinephric fat,
thickening of Gerota's fascia, and thick enhancing
septa separating hypodense areas in the renal
parenchyma. The hypodense areas in the periphery of
the renal mass are likely to be explained by xanthoma
cells or by incorporation of perinephric fat (6). No
single clinical or radiological sign is pathognomonic.
Percutaneous biopsy may be needed in selected cases
to confirm diagnosis (4). The definitive diagnosis
depends on histological examination of the operative
specimen.
In the literature only one case of focal XGP after renal
trauma was reported by Murayama et al. (13). It
involved a female patient with a history of blunt
trauma that could have caused renal injury.
Incidentally a renal mass was detected. With the
diagnosis of renal tumour, nephrectomy was
performed. Histopathological diagnosis was
xanthogranuloma of the kidney partly containing a
subcapsular hematoma. The presence of hematoma
and no evidence of suppurative lesions suggested that
the aetiology of xanthogranuloma in this case was
related to renal injury.
Conclusion
Focal XGP should be considered between the
differential diagnosis of renal masses.The diagnosis
may be suggested by the association of chronic
pyelonephritis, renal stones and hypovascular renal
tumour syndrome without specificity at sonography
and CT.
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