AJR 2003; 180:1278-1280
© American Roentgen Ray Society
Renal Mucormycosis in an AIDS Patient: Imaging Features and Pathologic Correlation
Ciaran F. Keogh1,
Jacqueline A. Brown1,
Peter Phillips2 and
Peter L. Cooperberg1
1 Department of Radiology, St. Paul's Hospital, 1081 Burrard St., Vancouver, B.
C., V6Z 1Y6 Canada.
2 Infectious Disease Clinic, St. Paul's Hospital, Vancouver, B. C.m V6Z 1Y6
Canada.
Received May 15, 2002;
accepted after revision September 26, 2002.
Address correspondence to J. A. Brown.
Introduction
Mucormycosis refers to infection by fungi of the order Mucorales
[1]. The organisms are
ubiquitous and tend to cause disease only in susceptible individuals,
classically those with diabetes mellitus or leukemia. The immunopathogenic
mechanisms resulting in mucormycosis are complex and poorly defined; despite
the associated immunosuppression, mucormycosis rarely occurs in patients with
AIDS [2]. Infection typically
involves the upper and lower airway but may be disseminated to other sites or
present as a generalized fulminant infection. Isolated renal mucormycosis is
exceptional: to our knowledge, it has been reported in only 19 previous
patients, nine of whom had AIDS
[3].
Our report illustrates the sonographic, CT, and previously unreported MR
imaging features of isolated renal mucormycosis in an AIDS patient.
Case Report
A 35-year-old woman presented with weight loss, fatigue, and left flank
pain. She had been treated 2 months previously for left-sided pyelonephritis,
but her symptoms had been slow to resolve. The patient had a history of IV
drug abuse and was HIV-positive (CD4 antigen count, < 10/mm3).
She was not undergoing antiretroviral or corticosteroid therapy. At clinical
examination, the patient was afebrile but was cachectic and had tenderness of
the left costovertebral angle. Laboratory investigations showed a normal WBC
count and normal renal function. In view of the persistent symptoms despite
antibacterial therapy, the possibility of a renal abscess or fungal infection
was raised, and the patient was referred for imaging.
Sonography showed the left kidney to be considerably enlarged. The renal
parenchyma was hypoechoic and had loss of corticomedullary differentiation.
Superior caliceal hydronephrosis was present as a result of a large focal
hypoechoic lesion in the lower pole. The main renal artery was patent, but
color flow in the kidney itself was reduced and in the lower pole mass was
completely absent. Sonographically guided aspiration of the lower pole mass
was performed with an 18-gauge needle. A small amount of purulent material was
obtained. The culture showed growth of Absidia species, one of the
organisms most commonly isolated from patients with mucormycosis.
Histopathology showed a filamentous fungus with morphologic features
compatible with Absidia organisms.
Helical CT (HiSpeed CT/i, General Electric Medical Systems, Milwaukee, WI)
of the abdomen was performed with iodinated contrast material (ioversal,
Optiray 320; Mallinckrodt Canada, Quebec, Canada) administered at 100 mL/sec
with a 65-sec delay, a 5-mm slice thickness, and a pitch of 1.7. The left
kidney was found to be enlarged. Enhancement was heterogeneous, with numerous
small areas of low attenuation throughout the kidney, suggestive of abscess
formation. The lower pole had been replaced by a solid 7.5-cm hypodense mass
or abscess. As shown on sonography, this entity compressed the renal pelvis,
resulting in upper caliceal dilatation. A small amount of perinephric fluid
was noted adjacent to the lower pole of the kidney. No contrast material
excretion was seen on the delayed scans. The renal artery and vein were patent
(Figs. 1A and
B). CT of the chest and the
remainder of the abdomen were unremarkable.
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Fig. 1A. —35-year-old woman with left flank pain who was HIV-positive
and had history of IV drug abuse. Contrast-enhanced axial CT scan acquired
through upper pole of left kidney shows upper caliceal hydronephrosis
(arrow) and heterogeneous enhancement with numerous small
hypodensities throughout renal parenchyma.
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Fig. 1B. —35-year-old woman with left flank pain who was HIV-positive
and had history of IV drug abuse. Contrast-enhanced axial CT scan acquired
through lower pole of the left kidney shows large hypodense area
(arrow) corresponding to abscess.
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Contrast-enhanced MR imaging was performed on a 0.5-T unit (Signa, General
Electric Medical Systems). T1-weighted imaging (TR/TE, 500/16.0; field of
view, 36 cm; slice thickness, 7 mm; excitations, 1) showed nephromegaly and
diffuse hypointensity of the kidney (Fig.
1C). On fast spin-echo T2-weighted imaging (3117/102; field of
view, 36 cm; echo-train length, 12; slice thickness, 7 mm), scant normal renal
tissue could be identified. Instead, the parenchyma was replaced by multiple
confluent hypointensities (Fig.
1D). This signal characteristic is unusual in inflammatory or
infective conditions in which high T2 signal because of edema usually
predominates. The hypointense areas represent fungus-filled abscesses,
containing thick necrotic debris rather than fluid. After gadolinium
administration, decreased heterogeneous enhancement was seen
(Fig. 1E). The T2
hypointensities did not enhance, confirming the presence of infarction and
necrosis. The adjacent organs and muscles appeared normal, without evidence of
invasion.
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Fig. 1C. —35-year-old woman with left flank pain who was HIV-positive
and had history of IV drug abuse. Axial T1-weighted MR image acquired through
mid kidneys shows that left kidney is enlarged and hypointense relative to
right. Focal hypointensity (arrow) represents dilated collecting
system.
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Fig. 1D. —35-year-old woman with left flank pain who was HIV-positive
and had history of IV drug abuse. Axial T2-weighted MR image of left kidney
shows marked heterogeneity and confluent hypointensities throughout
parenchyma. At histology (not shown), these findings corresponded to noncystic
infarction and fungus-filled abscesses. Focal caliceal dilatation
(arrow) is also present.
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Fig. 1E. —35-year-old woman with left flank pain who was HIV-positive
and had history of IV drug abuse. Axial nondynamic spin-echo T1-weighted MR
image obtained after gadolinium administration shows generalized decreased
enhancement in left kidney relative to right. Hypointense areas seen on
T2-weighted MR images (not shown) did not enhance, confirming presence of
infarction and necrosis.
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A left-sided nephrectomy was performed after the patient had received a
cumulative dose of 512 mg of amphotericin B. The bisected nephrectomy specimen
showed multiple necrotic yellow abscesses and areas of infarction
(Fig. 1F). On microscopic
examination, most of the renal parenchyma had been replaced by necrotic
inflammatory tissue. Broad aseptate hyphal forms consistent with
Absidia species were seen, similar to those of the cultured growth
from the aspirate.
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Fig. 1F. —35-year-old woman with left flank pain who was HIV-positive
and had history of IV drug abuse. Photograph of bisected nephrectomy specimen
in coronal view shows infarcted lower pole replaced by abscess and multiple
small abscesses throughout remainder of kidney.
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Postoperatively, the patient received further amphotericin B, and a salvage
antiretroviral regime was begun. At follow-up 12 months after nephrectomy, no
evidence of recurrent infection was seen.
Discussion
Mucorales fungi are ubiquitous and relatively avirulent but they may cause
severe infection in susceptible individuals
[1]. Mucormycosis most often
presents as a rhinocerebral syndrome or as pneumonia. Other clinical
manifestations may be cutaneous or gastrointestinal, involve the central
nervous system, or present as a disseminated infection. Isolated involvement
of other individual organs (e.g., bone, kidney, or heart) is rare. Certain
predisposing conditions are more commonly associated with specific
presentations of mucormycosis, such as diabetes mellitus and rhinocerebral
mucormycosis or kwashiorkor and gastrointestinal mucormycosis.
The pathogenic mechanisms resulting in infection are poorly understood but
appear to involve impaired granulocytic function and altered physical barriers
to infection [2]. The fungal
hyphae aggressively invade surrounding tissue and, characteristically,
adjacent blood vessels, leading to hemorrhage, thrombosis, and, ultimately,
infarction [1].
Mucormycosis among the HIV population is rare, especially when confined to
the kidney, but it is associated with IV drug abuse and a low CD4 antigen
count [2,
3]. IV inoculation with spores
is believed to contribute to renal and central nervous system dissemination
[2]. The clinical features are
usually consistent with pyelonephritis, although urologic symptoms may be
absent [2,
4,
5]. Renal involvement is
typically unilateral. Bilateral involvement carries a grave prognosis.
The CT and sonographic features of renal mucormycosis have been described
previously [4,
5,
6] and are similar to the
findings in our patient. The affected kidney tends to be enlarged, with
complete loss of normal renal architecture. Hypodense regions on CT correspond
to areas of infarction and abscess formation. The kidney is usually
nonfunctioning, and perinephric collections are common. Although no calculi
are present, the CT imaging features of renal mucormycosis are otherwise
similar to those found in xanthogranulomatous pyelonephritis, in which the
renal parenchyma is replaced by large aggregates of macrophages.
The MR imaging findings in this patient are interesting. In uncomplicated
acute bacterial pyelonephritis, the kidney shows increased signal on
T2-weighted sequences, indicating edema and inflammation
[7]. In renal mucormycosis,
however, cortical infarction and medullary necrosis dominate the pathologic
and imaging features because of the propensity of mucor to invade and cause
thrombosis in blood vessels. The reduced signal intensity on both T1- and
T2-weighted sequences and the relatively poor enhancement in our patient are
consistent with infarction and formation of fungus-filled abscesses that
contain thick necrotic debris rather than fluid.
Sonography is usually the modality of choice for investigation of
pyelonephritis and renal abscess. In severe cases, where intervention is
contemplated, both CT and MR imaging give a global perspective of the kidney
and its relationship to adjacent structures. The fact that MR imaging does not
require iodinated contrast material is an obvious advantage for patients with
renal impairment or diabetes mellitus, both of which are associated with
mucormycosis.
In the appropriate clinical setting, imaging features may strongly suggest
mucormycosis, but tissue is required for a definitive diagnosis
[1]. Renal biopsy or needle
aspiration may be performed. As was true in our patient, the aspirated
material tends to be extremely viscous, and in such cases, percutaneous
drainage is not possible [4].
Diagnosis is made by culture or by observing the irregularly shaped, broad
aseptate fungal hyphae with right-angle branching
[1].
Treatment of localized mucormycosis involves a medicochirurgic approach
that combines high-dose amphotericin B, nephrectomy, and reversal of
predisposing factors [1,
8]. The mortality rate of
mucormycosis remains high, even in the absence of dissemination; the reported
rate for primary renal disease is greater than 50%
[8].
In conclusion, primary renal mucormycosis is a rare infection. However, it
should be considered in the HIV-positive patient with a history of IV drug
abuse and symptoms of pyelonephritis that are unresponsive to therapy. Prompt
referral for imaging and biopsy or needle aspiration in the presence of the
described features—in particular, areas of reduced T2-weighted signal on
MR imaging—facilitate early diagnosis and may improve outcome.
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Introduction
Case Report
