Urinary tract infections can lead to pyelonephritis, an inflammation of the kidney that is diagnosed using clinical symptoms and laboratory tests. Imaging findings on ultrasound, CT, MRI, and nuclear medicine scans include wedge-shaped regions of reduced enhancement and perfusion in the kidney following infection originating in the bladder. While most cases are treated with antibiotics, imaging may be used to identify complications or guide management of high-risk patients.

2.  Urinary tract infections are the most common
urologic disease.
 Diagnosis is based on typical clinical symptoms
and laboratory findings.
 In general, imaging is not necessary for
diagnosis and treatment of uncomplicated
urinary tract infections in adult patients.
 However, diagnostic imaging demonstrates the
extent and nature of the urologic infections and
their potential complications.

3.  Urinary tract infection typically originates in
the urinary bladder;
 when it migrates to the kidney or is seeded
there hematogenously,
 a tubulointerstitial inflammatory reaction
ensues, involving the renal pelvis and
parenchyma.
 The condition is characterized as
PYELONEPHRITIS

4.  Immune suppression (AIDS, diabetes, corticosteroid
therapy, chemotherapy to treat cancer, kidney
transplant)
 Recent treatment with antibiotics for urothelial saprophyte
bacterial flora imbalance,
 Urinary catheter.
 Pregnancy.
 Obstruction to the urinary collecting system:
 Urinary lithiasis,
 deformity to the urinary system,
 Urothelial neoplasm,
 bladder neuropathy

5.  Associated with renal pelvic, renal
calyceal and renal parenchymal inflammation, and
comprises a heterogeneous group of conditions.
 bacterial pyelonephritis
 chronic pyelonephritis
 renal tuberculosis
 emphysematous pyelitis
 emphysematous pyelonephritis
 malacoplakia
 fungal pyelonephritis
 xanthogranulomatous pyelonephritis (XGP)

6.  inflammation of the mucosa and the
collecting system .
 On sonography this appears as echogenic
and even thickening around the
circumference of the walls of the collecting
system.
 This thickening is also seen on CT and MRI
scans, but sonography is usually sufficient to
put forward this diagnosis

7. Bilateral pyelitis: a: in the axial plane; b: in the sagittal plane. Even thickening
and contrast uptake in the walls of the renal
pelvis (white arrow). The presence of cortical defects is visible and this
corresponds to the sequelae of pyelonephritis (arrow-head)

8.  common and continues to have significant
morbidity in certain patients groups.
Epidemiology
 The incidence of acute pyelonephritis parallels
that of lower urinary tract infections:
approximately five times more common in
females with a sharp increase following
puberty .

9.  Clinical presentation is fairly specific and
classical in most cases, consisting of rapid
onset of High Fevers , Flank Pain And
Tenderness.
 White cells and bacteria are usually present in
the urine, and blood tests reveal the expected
changes: increased WCC, CRP and/or ESR.
In severe cases, systemic sepsis may be
present.
 In many instances patients respond promptly to
antibiotics and no imaging is required.

10.  The most commonly implicated organisms are from the
gastrointestinal tract :
 E. coli (most common)
 Klebsiella sp.
 Proteus sp.
 Enterobacter sp.
 Pseudomonas sp.
 Haemophilus influenzae

11.  Infection gains access to the upper urinary tract by passing retrogradely up
the ureter from the bladder, facilitated by virulence factors which allow
bacteria to adhere to the urothelium (e.g. adhesin P) and inhibit ureteric
peristalsis (endotoxins) .
 Infection then passes into the collecting tubules and results in an interstitial
nephritis, with resulting alterations in renal filtration and blood flow in the
affected region.
 Localised ischaemia secondary to inflammatory changes results in altered
imaging and potentially eventually results in necrosis and scarring .
 Rarely, the kidney may be seeded haematogeneously, in which case
usually peripherally located renal abscesses develop rather than
pyelonephritis.

12. In many instances imaging is not required.
Situations in which imaging is indicated include:
 Exclude obstructed kidney
 High risk patients: diabetics, elderly,
immunocompromised
 Those with mixed clinical picture
 Previous renal pathology

13.  Plain films have a limited role to play, especially
if patients are likely to go onto CT.
 They may demonstrate obstructing urinary tract
calculi and occasionally demonstrate gas within
the collecting system (emphysematous
pyelonephritis).
 Findings seen in cases of acute kidney
infections include renal enlargement, striated or
delayed nephrograms, delayed caliceal
appearance time, and dilatation or effacement
of the collecting system

14. Acute bacterial
pyelonephritis of the
left
kidney. Tomogram
from intravenous
pyelography
demonstrates an
enlarged left kidney
with effacement
of the central
collecting system.

15. Ultrasound is insensitive to the changes of acute pyelonephritis,
with most patients having 'normal' scan, and abnormalities only
identified in ~25% of cases .
Possible features include:
 particulate matter in the collecting system
 reduced areas of of cortical vascularity by using power Doppler
 gas bubbles (emphysematous pyelonephritis)
 abnormal echogenicity of the renal parenchyma
› focal/segmental hypoechoic regions
› mass like change
 Ultrasound is however useful in assessing for local
complications such as hydronephrosis,renal
abscess formation, renal infarction, perinephric collections, and
thus guiding management.

16. US shows a round shaped hyperechoic focus in the inferior pole of the right
kidney related to acute bacterial pyelonephritis. US also shows mild dilatation of the
collecting system in the right kidney.

17. (a) US scan shows a wedge-shaped hyperechoic focus (arrowhead)
in the upper pole of the right kidney related to acute bacterial pyelonephritis.
(b) Color flow US image demonstrates
diminished flow through the involved area.

18. Hipovascular area in the upper pole with power Doppler, due to acute
pyelonephritis.

19.  CT is the most sensitive modality for the renal tract, able to assess
for renal calculi, gas, perfusion defects, collections and obstruction
 Non-contrast CT
 Often the kidneys appear normal. Affected parts of the kidney typically
may appear swollen and of lower attenuation. Renal calculi or gas
within the collecting system may be evident.
 Post-contrast CT
 Following administration of contrast, one or more focal wedge like
regions will appear swollen and demonstrate reduced enhancement
compared to the normal portions of the kidney.
 The periphery of the cortex is also affected, helpful in distinguishing so
called lobar nephronia from a renal infarct (which tends to spare the
periphery; so-called rim sign).
 If imaged during the excretory phase, a striated nephrogram may also
be visible .
 If for some reason the kidney is imaged again within 3-6 hours,
persistent enhancement of the affected regions may be evident due to
slow flow of contrast through involved tubules .

20. CT without contrast material shows focal hyper-attenuation areas in the upper pole
of the right kidney which does not present enhancement with contrast administration,
findings suggestive of hemorrhagic acute bacterial pyelonephritis.

21. Right pyelonephritis on
a contrast-enhanced CT scan of the abdomen and pelvis in the tubular
venous phase: the renal parenchyma has a ‘‘spoked wheel’’
appearance.

22. (a) US image demonstrates a slightly enlarged right kidney that is
otherwise unremarkable, belying the advanced disease.
(b) CT scan shows the enlarged kidney with global decreased uptake of
contrast material and multiple small low-attenuation foci from abscess
pockets, findings
that prompted nephrectomy.

23. (a) US scan demonstrates a geographic,
slightly lobulated “mass” (arrowhead) in the midpole of the left kidney, a finding
that is worrisome for a solid tumor.
(b) CT scan shows multifocal regions of diminished enhancement that
extend to the periphery of the kidney, findings consistent with interstitial
nephritis.

24.  MRI is usually reserved for patients who are pregnant, and
findings mirror those seen on CT. The kidney demonstrates
wedge shaped regions of altered signal:
 T1: affected region(s) appear hypointense compared to normal
kidney parenchyma
 T2: hyperintense compared to normal kidney parenchyma
 T1 C+: reduced enhancement
 A fast inversion recovery sequence obtained after contrast
administration has been shown to be particularly effective in
outlining affected regions which appear hyperintense compared
to the low signal parenchyma. The contrast is thought to
represent a combination of local oedema, and decreased T2
signal due to Gadolinium in the perfused 'normal' portions .

25. Sagittal short inversiontime
inversion recovery image of the right
kidney obtained after gadolinium
administration
demonstrates signal drop off in the
normal middle and lower renal poles due
to normal perfusion and
uptake of contrast agent.
The infected upper pole, with its
compromised perfusion, remains bright
(arrowhead) and stands out in relief.

26.  Technetium-99m di-mercapto-succinic acid
(DMSA) demonstrates a similar reduction in
renal perfusion and function, which one or
more wedge like defects in the outline of the
kidneys .

27. Scintiscan obtained with
technetium 99m
di-mercapto-succinic acid
demonstrates
a photopenic, peripheral
defect
(arrow) in the upper lateral
margin of the
right kidney that correlates
with an area of
acute bacterial pyelonephritis

28.  Most patients respond rapidly to appropriate
antibiotic therapy, and often no imaging
whatsoever is required. Even when imaging has
been obtained, unless patients do not respond
clinically no follow-up imaging is usually required,
and it is important to note that imaging changes can
take up to five months to resolve .
 Presence of an upper urinary tract infection in the
presence of obstruction can threaten the viability of
the kidney and a percutaneous nephrostomy is
usually required on an emergency basis.

29.  Complications include :
 renal abscess
 renal infarction, necrosis and scarring
 chronic renal impairment
 hypertension

30.  General imaging differential considerations
include
 renal infarction
› typically spares the peripheral aspect of the
cortex, e.g. cortical rim sign
 other causes of interstitial nephritis
› sarcoidosis
› drug induced

31.  A form of pyelonephritis where there are
longstanding sequelae of renal infection.
 When acute pyelonephritis occurs repeatedly,
usually in relation to occult vesico-ureteric reflux,
this can lead to the patient developing fibrosing
interstitial nephritis
 Very often it progresses slowly into renal failure.
 May arises from multiple recurrent infections, or
represents stable changes from a remote single
infection, as radiographic differentiation between
the above scenarios can be challenging.

32.  General
 Imaging should be interpreted in the relevant clinical
context and is often characterised by
 renal scarring
 renal atrophy
 renal cortical thinning
 compensatory hypertrophy of residual normal tissue
(which may mimic a mass lesion)
 calyceal clubbing: secondary to retraction of the papilla
from overlying scar
 thickening and dilatation of the calyceal system
 overall renal asymmetry

33.  On SONOGRAPHY, atrophied kidneys appear small in
size, with dedifferentiation of the renal cortex and
medulla and the presence of cortical notches.
 If the patient’s renal function permits, a CONTRAST-
ENHANCED CT SCAN will lead to diagnosis. It
demonstrates the pyelonephritis scar tissue, which
combines cortical retraction with deformities of the
calyces, with areas in between that are comparatively
healthy.
 If there is no specific affected area, a RETROGRADE
CYSTOGRAPHY must be carried out to investigate
whether there is vesico-ureteric reflux.

34. (a) Unenhanced CT scan shows a small, deformed right kidney with multiple
deep scars and dystrophic calcifications.
(b) Photograph of the resected kidneys demonstrates extensive bilateral scar
formation.

35. Chronic pyelonephritis: a: axial view; b: coronal reconstruction. Pyelonephritis scar
tissue combining cortical retraction (white
arrows) and deformation of the calyces with areas in between that are
comparatively healthy seen on contrast-enhanced CT scan.

38.  Hypertension is frequently a long-term
sequela.
 Practical points
 Once the imaging changes of chronic
pyelonephritis have been established, repeat
imaging is seldom provides new findings.

40.  A subset of genitourinary tuberculosis,
accounts for 15-20% of extra-
pulmonary tuberculosis and can result in varied
and striking radiographic appearances.
 Tuberculosis can involve both the renal
parenchyma and the collecting system (calyces,
renal pelvis, ureter, bladder and urethra) and
results in different clinical presentations and
radiographic appearances.

41.  Clinical features are often non specific and
include:
 haematuria
 flank pain
 constitutional symptoms
 Diagnosis can be obtained by culturing multiple
first-morning-void urine samples, or by histology
of imaging guided biopsy or surgical specimens,
although as with tuberculosis infection
elsewhere the diagnosis is not always easy to
confirm 4.

42.  Renal infection results from haematogenous spread at the
time of primary infection, with multiple micro-abscesses
developing at the site of periglomerular capillary seeding.
 Normal host immunity is usually able to dampen the
disease with the usual development of a small inactive
granuloma.
 Usually there is a long latency between primary infection
and presentation which in most case occurs due to host
immunity becoming compromised.
 These quiescent granulomas then can reactivate, grow
and eventually communicate with the calyces, leading to
downstream infection.

43.  Both the renal parenchyma and the upper collecting
system (calyces and renal pelvis) can be involved. The
former is usually seen associated with the latter, which is
the most commonly involved site in the genitourinary tract.
 Infection limited to the renal parenchyma has two
morphological appearances :
 pyelonephritis
› appearances are similar to pyelonephritis caused by other
organisms
› hypoperfusion and swelling of all or part of the kidney
 pseudotumoural type
› single or multiple nodules
› mimics renal cell carcinoma

44.  Usually the collecting system is involved (either in isolation
or in combination with the parenchyma), and appearances
vary according to the stage of disease .
 early
› papillary necrosis (single or multiple) resulting in uneven
caliectasis
 progressive
› multifocal strictures and hydronephrosis
› mural thickening and enhancement (on cross-sectional
imaging)
 endstage
› progressive hydronephrosis and parenchymal thinning
› dystrophic calcification

45.  Plain film findings focus on calcification,
which is seen in 25-45%, at various stages
of disease.
 triangular in papillary necrosis
 focal or amorphous: putty kidney (endstage)

46. (a) Abdominal radiograph demonstrates extensive calcifications forming a cast of
the kidney and ureter.
(b) Photograph of the cut specimen shows complete replacement of the normal
kidney
by inflammatory debris

47.  Traditional plain film IVP is quite sensitive to renal
tuberculosis with only 10% of affected patients having
normal imaging. Features include:
 parenchymal scars 50%
 moth eaten calyces: early finding
 irregular caliectasis
 phantom calyx
 hydronephrosis
 Lower urinary tract signs (see bladder and ureteric
tuberculosis) also recognised include:
 Kerr kink
 sawtooth ureter
 pipe-stem ureter
 beaded or corkscrew ureter
 thimble bladder

48. Collimated image from intravenous urography
demonstrates
multiple papillary cavities.
Retrograde pyelogram shows that the upper
pole calix is stenotic (arrow) with associated
papillary necrosis.
The adjacent calix is fibrotic and distorted as

49.  Sonographic appearances are non-specific and variable, depending on
the stage of disease.
 early
› normal kidney or small focal cortical lesions with poorly defined border
› +/- calcification.
 progressive
› papillary destruction with echogenic masses near calyces
› distorted renal parenchyma
› irregular hypoechoic masses connecting to collecting system; no renal pelvic
dilatation
› mucosal thickening +/- ureteric and bladder involvement
› small, fibrotic thick-walled bladder
› echogenic foci or calcification (granulomas) in bladder wall near ureteric orifice
› localised or generalised pyonephrosis
 endstage
› small, shrunken kidney, "paper-thin" cortex and dense dystrophic calcification in
collecting system.
› may resemble chronic renal disease

50.  Ultrasound is less sensitive than CT in
detection of:
 calyceal, pelvic or ureteral abnormalities.
 isoechoic parenchymal masses.
 small calcifications.
 small cavities that communicate with
collecting system.

51.  CT is the most sensitive modality for visualising renal
calcifications and CT IVP is more sensitive at identifying all
manifestations of renal tuberculosis .
 early
› papillary necrosis (single or multiple) resulting in uneven caliectasis
 progressive
› multifocal strictures can affect any part of the collecting system
› generalised or focal hydronephrosis
› mural thickening and enhancement
› poorly enhancing renal parenchyma, either due to direct involvement or
due to hydronephrosis
 endstage
› progressive hydronephrosis results in very thin parenchyma, mimicking
multiple thin walled cysts
› amorphous dystrophic calcification eventually involves the entire kidney
(known as putty kidney)

52. Renal
tuberculosis.
Contrast
enhanced
nephrographic
phase CT shows
dilated
calices and
thining of the
renal cortex with
thin calcifications.

53.  Multi-drug treatment is essential, however
despite treatment, stricturing can progress.
 The role of nephrectomy is controversial and
depends on the degree of renal impairment,
bilateral vs unilateral disease and the status
of the lower urinary tract.
 Nephrectomy, partial nephrectomy or
cavernostomy can be performed both open
and endoscopically

54.  General imaging differential considerations
include:
 papillary necrosis
 medullary sponge kidney
 TCC (transitional cell carcinoma) of renal tract
 SCC (squamous cell carcinoma) of renal tract
 xanthogranulomatous pyelonephritis (XGP)


55.  Defined as isolated gas production inside the
excretory system, secondary to acute
bacterial infection
 It is relatively benign entity, and needs
accurate differentiation
from emphysematous pyelonephritis, which
is much morbid condition.
 It has excellent prognosis with good
response to medical management .

56.  Disease is more common in female,
 associated with diabetes and urinary tract
obstruction.
 Symptoms are usually mild, with fever and
chills. Sometimes flank tenderness with dysuria
is present.
Aetiology
 E. coli, Klebsiella, Aerobacter aerogenes and
Proteus mirabilis are the commonest causative
organisms.

57.  Plain film
 Retroperitoneal gas is seen in many patients.
Associated urolithiasis, if any, may also be
seen.
 Ultrasound
 May show dirty shadowing in pelvicalyceal
system.
 CT
 Gas-fluid level in dilated calyx, usually with mild
or no obvious features of pyelonephritis.

60.  Emphysematous pyelitis genrally carries a good
prognosis, and usually respond to intravenous
antibiotics followed by oral antibiotics .
 Differential diagnosis
 General considerations include
 emphysematous pyelonephritis
 reflux from emphysematous cystitis
 ileal ureterosigmoidostomy
 iatrogenic (ureteral instrumentation, radiological
intervention)
 fistulous connection with hollow viscus

61.  A morbid infection of kidneys, with characteristic
gas formation within or around the kidneys.
If not treated early, it may lead to fulminant
sepsis and carries a high mortality.
 Clinical presentation
 Flank pain, urinary tract obstruction with fever.
Leukocytosis and hyperglycemia (in diabetics)
are prominent lab findings. Thrombocytopenia
is particularly associated with poor prognosis 3.

62.  It tends to be more common in females.
Approximately 90% of patients have
uncontrolled diabetes 1. It may however also be
seen in immunocompromised individuals or
associated with urolithiasis, neoplasms or
sloughing of papilla.
 Causative organisms include
 E. Coli: usually considered the commonest
causative organism 3
 Klebsiella pneumonia
 Proteus mirabilis

63.  Plain film and fluoroscopy (IVP)
 May show mottled gas within renal fossa or
crescentic gas collection within Gerota's
fascia. Linear gas shadows along paraspinal
region may also be seen, representing
retroperitoneal air.

65.  may show an enlarged kidney with coarse
echoes within renal parenchyma or collecting
system.
 dirty echogenic foci with reverberation/ring-
down artifacts representing air ('dirty
shadowing') may also be seen
 Bowel gas over kidneys may lead to false
positive diagnosis.

67.  CT is the best diagnostic modality for
emphysematous pyelonephritis. It may show
following diagnostic features
 enlarged, destructed renal parenchyma
 small bubbly or linear streaks of gas 1
 fluid collections, with gas-fluid levels
 focal necrotic areas +/- abscess

69.  CT features of emphysematous pyelonephritis
differentiates into two types:
 type 1
› renal parenchymal destruction with streaky or mottled
appearance of gas
› intra- or extrarenal fluid collections are characteristically
absent
› it is usually more aggressive and lead to death shortly, if
not intervened early
 type 2
› renal or extrarenal collections associated with bubbly or
loculated gas, or gas within pelvicalyceal system or ureter

70. The huang-tseng CT classification system
 Class 1: gas in collecting system only
 Class 2: gas in renal parenchyma only (without
extrarenal extension)
 Class 3: gas in renal parenchyma with extrarenal
extension
› Class 3a: extension of gas or abscess to perinephric
space
› Class 3b: extension of gas or abscess to pararenal space
 Class 4: bilateral emphysematous pyelonephritis or
solitary kidney with emphysematous pyelonephritis

71.  Treatment and prognosis
 In mild cases, intravenous antibiotics are
administered and percutaneous catheter
drainage of perirenal or retroperitoneal
collections is done. Severe cases often
warrant a nephrectomy.

72.  Differential diagnosis
 General imaging differential considerations
include
 emphysematous pyelitis
 iatrogenic (instrumentation, or intervention of
urinary tract)
 ureter-ileosigmoidostomy or fistulous
communication with bowel

73.  Malacoplakia of the urinary system is the
commonest manifestation of malakoplakia. The
latter, meaning soft plaque, is a rare chronic
granulomatous condition that can affect any
organ.
 Epidemiology
 Malacoplakia has a peak incidence in middle
age, and has a female-to-male ratio of 4:11. The
disease is more common in patients who are
immunocompromised or those with diabetes
mellitus.

74.  Presenting symptoms include gross hematuria and signs of
urinary tract infection, with Escherichia coli infection being very
commonly found to coexist.
 Pathology
 Although infection with E. Coli is very commonly observed, and
it is thought to play a part in the pathogenesis of malacoplakia,
other factors are also suspected, particularly impaired host
defenses and defective phagocytosis 1.
 The histologic hallmark of the disorder is the presence of
basophilic inclusions, caIledMichaelis-Gutmann bodies in large
eosinophilic macrophage2.
 Location
 Within the urinary tract, the bladder is the most frequently
affected organ (40% of patients with malacoplakia)

75.  Imaging characteristics of malacoplakia are
varied, and most commonly observed within the
bladder, although plaques may also occur in the
ureters.
 Malacoplakia may present as multiple, polypoid,
vascular, solid masses or as circumferential wall
thickening, associated with vesicoureteral
reflux and dilatation of the upper urinary tract.
These masses vary in size from a
few millimeters to several centimeters.

76. (a, b) Unenhanced CT images obtained at different levels (a higher
than b) demonstrate
symmetrically enlarged kidneys.

77. Corresponding T1-weighted MR image shows globally enlarged kidneys of
intermediate
signal intensity.
(d) Photograph of the bisected specimen reveals a whitish infiltrate that
nearly completely
replaces the renal parenchyma.

78.  Although malacoplakia may be extremely
aggressive, invading the perivesical space,
and it can even cause bone destruction, non-
surgical medical management is the
mainstay of treatment, and as such biopsy
for accurate diagnosis is essential.
 Treatment regimens include antibiotics,
ascorbic acid, and a cholinergic agonist 1.

79.  The urinary system can be colonised by
Candida Albicans either by the ascending or
haematogenous route in immune suppressed
patients.
 Based on the clinical presentation and
laboratory results, it is sometimes difficult to
distinguish a colonisation from an infection.
 However, the presence of Candida is always
pathological. If it is present this points to
systemic candidiasis and renal involvement is
likely where it is also present in the urine.

80.  Sonography detects accumulation of mycelia
with a variable appearance: hyperechoic,
minimally echoic or slightly echoic.
 This is also visible on IVU or pyelography.
Lesions of the renal parenchyma do not
show any specific features.

81.  On CT scanning, the mycelial accumulation
does not take up the contrast medium. It has
a rolled appearance when it contains gas
between the layers of fungal colonies. When
gas is absent, it appears as an aspecific but
mobile solid mass. On an excretory phase
CT scan, a filling defect in the collecting
system can be seen.

82.  A rare form of chronic pyelonephritisand represents
a chronic granulomatous disease resulting in a non-
functioning kidney. Radiographic features are
usually specific.
 Epidemiology
 Xanthogranulomatous pyelonephritis is seen
essentially in all age groups, but most frequently
presents in middle-aged to elderly patients .
 There is a female predilection (F:M 2:1)
presumably relating to an increased incidence of
urinary tract infections and thus struvite (staghorn)
calculi.

83.  Clinical presentation is typically vague, consisting of
constitutional symptoms such as
 Malaise,
 Weight loss and
 Low grade fever.
 Haematuria and flank pain are sometimes
encountered .
 Despite often absent urinary tract symptoms, pyuria
and positive urinary cultures are present in the
majority of cases (95 and 60% respectively) .

84.  Xanthogranulomatous pyelonephritis is, as the name
suggests, a chronic granulomatous process believed to
be the result of subacute/chronic infection inciting a
chronic but incomplete immune reaction .
 The kidney is eventually replaced by a mass of reactive
tissue, surrounding the usually present (90%)
inciting staghorn calculus with
associated hydronephrosis of a greater or lesser degree.
Foamy (lipid laden) macrophages predominate .
 Inflammatory process eventually extends into perinephric
tissues and even adjacent organs .
 Various bacteria are isolated, however the most commonly
isolated species are E coli andP mirabilis .

85.  Two forms of the disease are recognised
both macroscopically and on imaging :
 diffuse: 90% of cases
 focal: 10% of cases
› sometimes truly a focal process in a normal
kidney
› in other instances this represents diffuse XGP of
one moiety of a duplex system

86.  Plain film
 Plain film findings are difficult to distinguish
from a routine staghorn calculus, although
fragmentation and enlargement of the the
renal outline may be seen. A calculus is not
always present; in such cases it is not
possible to make a plain film diagnosis.

88.  Ultrasound examination demonstrate an
enlarged and distorted renal outline, with
loss of the normal renal architecture and
(usually) a centrally located shadowing
calculus.

90.  CT findings are most helpful in reaching the correct
diagnosis. The normal renal outline is lost and
enlarged with paradoxical contracted renal pelvis.
The calyces in contrast, are dilated giving a
multloculated appearance that has been likened to
the paw print of a bear (bear's paw sign) .
Sometimes there is perinephric extension
with thickening of the Gerota's fascia. Calcification
can be better delineated on CT scan.
 CT or conventional urography
 In most cases there is little if any renal function in
the affected kidney .

92.  MRI appearances mirror the heterogeneous
nature of the mass with solid and cystic
components surrounding a central staghorn
calculus. As such signal is heterogeneous on
all sequences.

94.  By the time xanthogranulomatous
pyelonephritis has become established, no
conservative or medical therapies exist.
Surgical nephrectomy is usually curative .
The presence of inflammatory reaction in
adjacent tissues often requires a large
operative field and an anterolateral
transperitoneal approach .

95.  The differential is narrow when the entire kidney is
affected and cross-sectional imaging has been
obtained, and is largely limited to renal tuberculosis,
which however usually results in a shrunken
calcified putty kidney.
 In cases where typical features are not present
(e.g. no staghorn calculus, focal disease only) then
other entities to be considered include:
 renal tuberculosis
 renal abscess
 renal cell carcinoma (RCC)
 angiomyolipoma (AML): with minimal fat

96. Thank you