Imaging of Non tubercular infections of the urinary tract

NON TUBERCULAR INFECTIONS OF THE
URINARY TRACT

INTRODUCTION
 Acute
 Chronic infections
Acute renal infections
Acute pyelonephritis and its various
complications such as focal bacterial
nephritis
(FBN),
Renal abscess,
Emphysematous pyelonephritis,
Papillary necrosis and
Pyonephrosis

Chronic renal infections
Chronic pyelonephritis,
Reflux nephropathy,
Xanthogranulomatous
pyelonephritis, Malacoplakia,
Squamous metaplasia and
Cholesteatoma.

 Plain X-ray and intravenous urography (IVU) have a declining role
whereas ultrasonography (US), computed tomography (CT) and
magnetic resonance imaging (MRI) play a vital role in detection and
delineation of the extent of renal infectious diseases.
 Plain X-ray
- Abnormal gas collection in the renal or perirenal area in
emphysematous pyelonephritis
- Renal abscess or stag-horn calculus in a patient suspected to
have pyonephrosis .
 IVU - Limited role
- Can exclude congenital anomalies ,
- Papillary necrosis and early tuberculosis may be diagnosed

CT
- Gold standard for diagnosis as well as for delineating the
extent of renal infective diseases .
MRI
- Being increasingly used as an
effective modality for both medical and
surgical diseases of kidney especially in
pregnant women, in patients with renal failure
where iodinated contrast cannot be used and in
diabetics
Radionuclide studies with cortical scintigraphy agents
such as 99mTc DMSA and glucoheptonate have been
shown to be the most sensitive techniques for the
diagnosis of acute pyelonephritis and detection of the
renal scars in reflux nephropathy

Plain X-ray abdomen showing a large loculus of air overlying the right renal
area in a diabetic patient with extensive emphysematous pyelonephritis

ACUTE INFECTIONS
ACUTE PYELONEPHRITIS
 Inflammatory process affecting the collecting system
and the renal interstitium
 Usually bacterial but may be fungal or viral
 Predisposing factors
prolonged catheter drainage,
reflux,
obstruction,
congenital anomalies,
diabetes and
pregnancy .

Ultrasound
-- Less sensitive
-- Focal or diffuse enlargement of the kidney with low level echoes .
-- Loss of corticomedullary (CM) differentiation .
-- gas bubbles (emphysematous pyelonephritis)
-- abnormal echogenicity of the renal parenchyma 1
◦ focal/segmental hypoechoic regions (in edema) or hyperechoic
regions (in haemorrhage)
◦ mass-like change
CONTRAST ULTRASOUND
-- Areas of poor perfusion related to nephritis .
-- Power Doppler is superior to colour Doppler in defining extent of
hypoperfusion .
-- Modality of choice for pregnant patients

IVP
-- less sensitive , Only 25 percent of cases of acute
pyelonephritis will have positive IVU findings
-- global or focal renal enlargement with decreased, delayed,
and persistent nephrogram
-- Pelvicalyceal system may show minimal dilatation or
attenuation of the calyces
-- In severe cases, the picture may resemble renal vein
thrombosis or replacement of the renal tissue with tumor

Non-contrast CT
-- often the kidneys appear normal
-- affected parts of the kidney may appear oedematous, i.e. swollen and of
lower attenuation
-- renal calculi or gas within the collecting system may be evident
Postcontrast CT
-- one or more focal wedge-like regions will appear swollen and
demonstrate reduced enhancement compared with the normal portions
of the kidney
-- the periphery of the cortex is also affected, helpful in distinguishing acute
pyelonephritis from a renal infarct (which tends to spare the periphery;
the so-called 'rim sign')
-- if imaged during the excretory phase, a striated nephrogram may also
be visible

MRI
T1 affected region(s) appear hypointense compared with the
normal kidney parenchyma
T2 hyperintense compared to normal kidney parenchyma
T1 C+ reduced enhancement
Nuclear medicine
Technetium-99m dimercaptosuccinic acid (DMSA) demonstrates
a similar reduction in renal perfusion and function, which
appears as one or more patchy scintigraphy defects in the
outline of the kidneys .

Diffusely hypoechoic and thickened cortex
with compressed renal sinuses.

Contrast-enhanced CT scan shows bilateral
enlarged kidneys with striated nephrogram
(arrows) suggestive of acute pyelonephritis.
There is presence of perinephric stranding and
thickening of Gerota’s fascia and lateral conal
fascia
Left renal enlargement, with patchy or
striated nephrogram and cortical wedge-
shaped areas of decreased density. There
is a loss of normal corticomedullary
differentiation with multiple peripheral
& cortical abscesses. There is a thickening
of walls of renal pelvis, calyces and
proximal ureter with abnormal
enhancement.

Imaging differential diagnosis - Renal infarction
cortical rim sign
useful in distinguishing acute pyelonephritis from a segmental renal
infarct and is seen on contrast enhanced CT or MRI.
 The wedges of reduced enhancement seen in the setting of acute
pyelonephritis represent oedema and ischaemia which involves the
whole wedge or renal parenchyma, from medulla to the
capsule. This sign seen as a result of cortical necrosis may also be
seen in conditions like renal transplant rejection, intravascular
haemolysis, shock, and as a consequence of obstetric complication.
 In segmental infarcts, the blood supply to the outer aspect of the
cortex is derived from perforating branches of the renal capsular
artery which is an early branch of the renal artery. As such, when a
branch of the renal artery is occluded (by
thromboembolism, dissection, etc) perfusion may be preserved to a
thin rim (2-4 mm) of cortex which enhances normally.
 Unfortunately the cortical rim sign is only seen in approximately half

Absent cortical rim sign -
pyelonephritis
Renal infarct with subtle but
present cortical rim sign.

DMSA scan
Scintiscan obtained with technetium 99m
dimercaptosuccinic 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.

ACUTE FOCAL BACTERIAL NEPHRITIS
 IVU
focal renal mass which on follow-up IVU may reveal an area
of focal scarring due to healing opposite a normal or clubbed
calyx.
 ultrasound
hypoechoic poorly defined mass with internal
echoes
 CT
low density area with patchy enhancement
Lack of well defined wall and central low density
differentiates it from the renal abscess.

ACUTE FOCAL BACTERIAL NEPHRITIS
(A) Longitudinal ultrasound scan of the
kidney showing poorly defined
hypoechoic lesion with low level
internal echoes in the upper polar
region (arrow) which was due to focal
bacterial nephritis.
(B) Contrast enhanced CT scan of another
patient showing a focal low density
area with patchy enhancement in the
posterior aspect of upper pole of left
kidney (arrow)

RENAL AND PERIRENAL ABSCESS
complication of focal bacterial pyelonephritis, but may result
from haematogenous infection or superadded infection in a
renal cyst or direct involvement of the perinephric space from
pancreas, colon, and retroperitoneum
Plain X-ray abdomen
hows renal enlargement, rotation, displacement, presence of
mottled gas in the renal areas, and loss of psoas outline.
IVU
shows poorly or nonfunctioning kidney with calyceal
attenuation and compression due to mass affect.
Ultrasound
well-defined complex mass with good sound transmission
Bright echoes with dirty distal shadowing are seen
in the presence of air.

CT
Gold standard to assess the renal as well as extrarenal extent of
the renal abscess.
changes in the renal contour, parenchymal density,
enhancement pattern and perinephric abnormalities such as
thickening of the Gerota’s fascia, psoas muscle involvement are
best seen on CT
Presence of nonenhancing poorly marginated area of
decreased attenuation may be seen during the earlier course of
renal abscess
Later in the course of the disease, renal abscess appears as a
sharply marginated area of low attenuation due to necrosis
surrounded by a peripheral enhancing rim indicating a mature
abscess

MRI
 hypointense lesion on T1WI
 hyperintense lesion on T2WI
 Gadolinium administration the lesion shows
peripheral enhancement
Differential diagnosis :
Segmental renal infarct,
Metastasis,
Lymphoma,
Trauma, and
Renal vein thrombosis

(A) IVU showing a mass
impression on the collecting
system of the upper pole and
pelvis due to a right renal
abscess. The lower group of
calyces are not visualized.
The psoas shadow on the
ipsilateral side is also
obliterated.
(B) Contrast-enhanced CT scan
of the same patient showing an
absent nephrogram in the lower
pole with a liquefied
collection in the perinephric
space (arrow) extending
medially into the right psoas
muscle

 (B) Contrast-enhanced CT scan of the same patient
shows a well-defined hypodense lesion in the
anterior parenchyma with minimal peripheral
contrast enhancement (B) Contrast-enhanced CT
scan of the same patient
shows a well-defined hypodense lesion in the
anterior parenchyma with minimal peripheral
contrast
(A) Longitudinal ultrasound scan
of the transplant kidney shows an
anechoic lesion with internal
debris in the interpolar region
(arrow) suggestive of abscess.
(B) Contrast-enhanced CT scan of
the same patient shows a well-
defined hypodense lesion in the
anterior parenchyma with minimal
peripheral contrast enhancement

Contrast-enhanced CT scan
showing multiple
low density lesions with rim
enhancement in the right
kidney
suggestive of renal abscess
with extension into the
perinephric space

EMPHYSEMATOUS PYELONEPHRITIS
 indicates severe renal infection with gasforming
organisms characterized by presence of gas in the
collecting system or renal parenchyma.
Two types:
Type I - less common (33%),
parenchyma destruction and shows
streaky/mottled gas in interstitium of renal
parenchyma radiating from medulla to cortex,
crescent of subcapsular/perinephric gas with no
fluid
collection.
Type II - more common (66%)
shows bubbly/loculated intrarenal gas,
renal/perirenal fluid collections and gas within the
pelvicalyceal system.

Plain X-ray
 Air specks in renal area.
 frequently misinterpreted as bowel gas.
US
 Dense echoes with dirty shadowing in intrarenal infection.
 If the gas enters the perinephric space, there will be nonvisualization of kidney
(gassed out kidney)
CT
 detects the presence of air, its precise location within the kidney as well as its
extension into the perirenal or pararenal compartments of the retroperitoneal
space.
MRI
 limited as gas appears as an area of signal loss which cannot be differentiated
from calculi, renal calcification

Extensive gas overlying the renal
parenchyma, collecting system and
perinephric tissues on the right
side. Additional linear gas shadows along
paraspinal region, representing
retroperitoneal air.
Contrast-enhanced CT scan showing left
renal
calculi and dilated collecting system with
dense urine suggestive of pyonephrosis. In
addition extensive collection of air is seen
in the renal parenchyma and perinephric
space with extension around the aorta due
to emphysematous pyelonephritis

PYONEPHROSIS
 Infection in an obstructed collecting system with suppurative
destruction of the renal parenchyma.
US - the modality of choice to detect dilated collecting system which
contains dependent echoes and shifting debris.
CT -ideal to show intrarenal changes and the perirenal extension.
High-density of urine in the dilated system should suggest
infection
 Thickening of the renal pelvic wall may be detected both on US or
CT.
 Ultrasound guided aspiration may be performed to confirm the
diagnosis as well as obtain specimen for culture and sensitivity.
 Percutaneous nephrostomy may also be performed under US
guidance to provide immediate decompression of the collecting
system as an adjunct prior to definitive surgery.

(A) Longitudinal ultrasound scan of
right kidney showing dilated
collecting system filled with
echogenic material and thickened
echogenic uroepithelium
(arrow) suggestive of pyonephrosis.
(B) Contrastenhanced CT scan
shows hydronephrosis of left kidney
with presence of high density urine
and perinephric and periureteric
stranding (arrow). (C) Caudal axial
section in
the same patient shows a left lower
ureteric calculus

Chronic pyelonephritis
 Chronic inflammation of the kidney characterized by
cortical scarring overlying the involved calyx (usually
polar).
 Entire collecting system may be involved resulting in
small kidney with clubbed calyces.
Differential diagnosis
Fetal lobulation,
Ischemia
Hypoplastic kidney

REFLUX NEPHROPATHY
 Results from combined effects of the vesicoureteric
reflux and bacterial infection.
 Begins in infancy and childhood, and is more
common in females.
 Incompetent papillary duct orifices.
 Intrarenal reflux of infected urine which leads to
destruction of the tubules and subsequent
scarring.
Fluoroscopic voiding cystourethrogram
US - best screening tool to detect obstructive
uropathy.
Renal cortical scintigraphy - best technique to
detect renal scarring.

FAT PROLIFERATION IN THE KIDNEY
 Sinus fat may increase as a normal phenomenon in
an aging kidney, renal sinus lipomatosis (RSL)
 usually seen in patients with extrarenal pelvis.
 Differentiation from a parapelvic cyst may require
ultrasonography.
Contrast- enhanced CT scan shows an
enlarged renal sinus (arrow) with fat
attenuation on the left side suggestive of
renal sinus lipomatosis. The fat attenuation
differentiates renal sinus lipomatosis from
parapelvic cyst
Differential diagnosis - fat containing
tumors such as angiomyolipoma.

XANTHOGRANULOMATOUS PYELONEPHRITIS
 Chronic granulomatous inflammation of the kidney
usually seen in patients who have stones and obstruction.
 Replacement of the renal parenchyma with lipidladen
macrophages which are paraaminosalicylic acid (PAS)-
positive (xanthoma cells).
 common in women
plain X-ray
Presence of staghorn calculus and/or also small
calcifications.
IVU
Focal mass (tumefactive type), or diffusely enlarged
nonfunctioning kidney.
CT
Presence of lucent areas on X-ray and nonenhancing
cystic areas on CT corresponding to the xanthoma cell
collection is characteristic.

Contrast-enhanced CT scan shows right
renal
calculi with a well- defined mass lesion with
multiple fat attenuation areas (arrow)
characteristic of xanthoma cell collection in
a case of xantho-granulomatous
pyelonephritis
XANTHOGRANULOMATOUS PYELONEPHRITIS
Differential diagnosis
Pyonephrosis,
Tuberculosis,
Cystic carcinoma,
Lymphoma

Single image from the CT
with the right kidney
outlined. Note how the
dilated low density calyces
form an appearance which
has been likened to that of
the pads of a bear paw.

RENAL PAPILLARY NECROSIS
 Most common cause of renal papillary
necrosis is analgesic abuse and diabetes.
other causes
urinary tract infection (UTI),
renal vein thrombosis,
obstruction,
dehydration, and
sickle cell disease.

IVU
 Best technique for demonstrating the changes of papillary
necrosis.
 Presence of extracalyceal contrast, ill-defined calyx, contrast
outlining sloughed papillae (ring sign), and filling defect in the
calyx
Classical features may appear as
 ball on tee
 forniceal excavation
 lobster claw
 signet ring
 sloughed papilla with clubbed calyx
RENAL PAPILLARY NECROSIS

Normal calyx and "lobster claw" papillary necrosis.

MALACOPLAKIA
 Granulomatous inflammatory disease seen almost exclusively
in women who present with repeated attacks of UTI.
 Bladder and ureter are most frequently affected.
Radiological features
 Enlarged poorly functioning kidney
 Filling defect in the bladder and the ureter, similar to the
changes seen in pyeloureteritis cystica,
 transitional cell carcinoma.
 Strictures may also form, thus
tuberculosis is an important differential diagnosis.

SQUAMOUS METAPLASIA
 Replacement of normal transitional cell epithelium by
squamous epithelium as a result of infection.
 Presence of multiple linear radiolucencies in the ureter due to
mucosal thickening resulting in so called “tree barking” or
“Corduroy appearance” in IVU or RGU.
 The term, cholesteatoma is used when there is a filling defect in
the collecting system due to sloughed keratinized material.
PARASITIC INFECTION
 Schistosomis usually affects the bladder causing calcification.
 Intrarenal hydatids are rare - focal cystic masses which are
usually thick walled and irregular, and may show calcification of
crushed eggshell pattern.

(A) Excretory urogram showing a mass
at the lower pole of right kidney with
displacement and dilatation of the
collecting system and medial deviation
of
the ureter.
(B and C) Ultrasound and contrast-
enhanced
CT scan of the same patient showing
characteristic multiloculated
appearance due to daughter cysts of
hydatid later confirmed at surgery

Imaging of Non tubercular infections of the urinary tract

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