Air in the kidney: between emphysematous pyelitis and pyelonephritis
Department of Biomedical Imaging, Faculty of Medicine, University of Malaya, Kuala Lumpur
Presence of air in the kidney can be problematic as the
location of the air in different parts of the kidney greatly affects the
subsequent management and outcome of the patient. We present here a case of a
patient who had emphysematous pyelitis, in which CT scan was able to display
presence of air only in the collecting system, thus differentiating this
condition from the more fulminant emphysematous pyelonephritis. This leads to a
more favourable prognosis and outcome to the patient. � 2008 Biomedical
Imaging and Intervention Journal. All rights reserved.
Keywords: Emphysematous pyelitis, emphysematous
pyelonephritis, CT scan
Emphysematous (gas-forming) infections in the abdomen and
pelvis represent potentially life-threatening conditions that require
aggressive medical and, often, surgical management. They frequently progress
rapidly to sepsis in the absence of any early therapeutic interventions .
However, among the entities of gas-forming infections, there is a condition
called emphysematous pyelitis where the prognosis is excellent, with rapid
complete recovery after medical treatment .
Emphysematous pyelitis is the term used to describe the
presence of gas limited to the renal excretory system . It is a benign
condition with a low overall mortality rate as compared to emphysematous
pyelonephritis . Thus, it is important to distinguish between these two
types of gas-forming renal infections because of the prognostic differences and,
hence, the differences in clinical management.
We present a case of emphysematous pyelitis diagnosed on
CT scan. Described are the imaging findings in emphysematous pyelitis and how
they differ from findings in emphysematous pyelonephritis. We will further
discuss the clinical management of the two entities.
Mr SM is a 63-year-old Indian man with a history of
diabetes mellitus and hypertension. He presented to the trauma and emergency
department with a two-day history of dysuria, haematuria and suprapubic pain.
He also reported having intermittent fever over the past week. Clinically, he
was afebrile and his vital signs were stable. His abdomen was soft, revealing
tenderness only at the suprapubic region.
His abdominal radiograph taken in supine position revealed
an oval radiopacity measuring 4 x 4cm surrounded by a radiolucent rim at the
region of the left kidney (Figure 1). A provisional diagnosis of a gas-forming
infection of the left kidney was made. Subsequent ultrasound revealed multiple
echogenic lines associated with dirty shadowing (containing low-level echoes
and reverberations) at the region of the sinus of the left kidney in keeping
with gas formation. There was another echogenic focus with �clean� shadow noted
posteriorly in keeping with calculus. However, the exact position of the gas
and calculus in relation to the left kidney and the pelvicalyceal system could
not be delineated due to the presence of their shadows. At this time, it was
imperative to rule out emphysematous pyelonephritis in this patient.
An urgent plain and contrasted CT abdomen and pelvis was
performed. There was a large obstructing calculus noted at the left
pelvi-ureteric junction causing gross left hydronephrosis with gas noted within
the left pelvicalyceal system (Figure 2 and Figure 3). However, there were no
gas pockets or fluid collections seen within the left renal parenchyma or in
the left perinephric tissues. The urinary bladder showed no presence of air as
Diagnosis of emphysematous pyelitis was made based on the
CT findings. Subsequently an urgent left nephrostomy was arranged and was done
later on the day of admission. Intravenous antibiotics (IV Cefobid 2g BD and IV
Tazosin 4.5g) were commenced on the same day. Patient responded favourably to
the treatment with no fever recorded in the ward. A left JJ stent was inserted
and the patient was subsequently discharged. ESWL (extracorporeal shock wave
lithotripsy) was planned for the patient on a later date.
Emphysematous pyelitis is a rare infection of the urinary
collecting system due to gas forming bacteria [1, 3]. Emphysematous pyelitis
carries a mortality rate of up to 20%, which is significantly lower than that
of emphysematous pyelonephritis, which carries a mortality rate of
approximately 50% . It is often associated with underlying diabetes although
the relationship with diabetes mellitus is lower than in emphysematous
pyelonephritis . Underlying poorly-controlled diabetes mellitus is present
in up to 90% of patients who develop emphysematous pyelonephritis  compared
to only 50% of patients with emphysematous pyelitis who have diabetes mellitus .
Emphysematous pyelitis usually accompanies urinary tract obstruction of which
the cause of obstruction is usually calculi . The patient in this case had
both diabetes mellitus and obstructing pelvi-ureteric calculus.
The clinical manifestation of emphysematous pyelitis tends
to be non-specific, similar to the clinical presentation of uncomplicated acute
pyelonephritis . Roy et al reported five patients, who were eventually
diagnosed with emphysematous pyelitis, all had a one-week history of fever and
chills at presentation. These symptoms were associated with upper-quadrant
tenderness on either side depending on where the pathology was. Four of the
patients had dysuria, and one had pyuria. Macroscopic haematuria was found in
one patient . The patient in our case presented with symptoms of urinary
tract infection with fever, dysuria, haematuria and suprapubic pain; very
similar to the cases documented by Roy et al except that there was no loin or
upper-quadrant tenderness. On the contrary, most patients with emphysematous
pyelonephritis are severely ill with chills, fever, flank pain, frequent
lethargy and confusion, and multiple associated medical problems such as
uncontrolled hyperglycaemia, acidosis, dehydration and electrolyte imbalance .
A typical feature seen in conventional radiography of
emphysematous pyelitis is the presence of gas outlining the ureters and
pelvicalyceal system. The rate of diagnosis with plain radiography is low
because of intestinal gases . In this case, due to the obstructing ureteric
calculus, the presence of gas was concentrated in the dilated pelvis of the
left kidney. Ultrasound findings include high-amplitude shadowing along the non-dependent
surfaces that was present in this case causing obscuration of the posterior
structures. The posterior shadowing is typically �dirty� as opposed to the
�clean� shadowing caused by calculus. Kiris et al reported ultrasound findings
that were different from the typical appearances. The gas appeared as a hypoechogenic
area surrounded by an echogenic (calcific) rim and more echogenic central stone,
thus giving the appearance of a target sign .
Finally, a CT scan was performed as this best delineates
gas within the collecting system and helps reliably identify ureteric stones as
demonstrated in this case. Based on the CT appearance, the diagnosis of
emphysematous pyelonephritis could be excluded because there were no gas
pockets or fluid collections within the renal parenchyma or perinephric tissue.
Gas appearance inside the urinary system can be caused by
infections due to gas-producing bacteria, fistulas related to the
gastrointestinal system, gas reflux from the urinary bladder, trauma and the urinary
system�s interventional procedures . Common bacterial causes of
emphysematous pyelitis are E. Coli, K. pneumonia and Aerobacter
. No organism was cultured from the urine sample in this case although the
urine microscopy revealed packed field of leucocytes and 2+ of bacteria.
Emphysematous pyelonephritis has been defined as an acute,
severe, necrotising infection of the renal parenchyma and perirenal tissue,
which results in the presence of gas within the renal parenchyma, collecting
system, or perinephric tissue . A CT classification scheme proposed by Wan
et al  divides emphysematous pyelonephritis into two types with different
prognostic significance. Type I emphysematous pyelonephritis is characterised
by parenchymal destruction with streaky or mottled gas collections but no fluid
collections. Type II emphysematous pyelonephritis is characterised by bubbly or
loculated gas within the parenchyma or collecting system with associated renal
or perirenal fluid collections that are thought to represent a favorable immune
response. Based on these descriptions by Wan et al, emphysematous pyelitis
falls under Type II emphysematous pyelonephritis which carries a mortality rate
of 18% versus 69% for Type I . In the classical Type I emphysematous
pyelonephritis, a reduced immune response limits the formation of pus
collection and this leads to the spread of the inflammation culminating in a fulminant
course of the disease. In contrast, a better immune response in Type II
emphysematous pyelonephritis causes formation of pus in the kidney leading to a
slower course of the disease and a better prognosis [5, 6].
The clinical management of emphysematous pyelitis and
emphysematous pyelonephritis are different. Intraparenchymal gas usually
requires drainage or nephrectomy and is associated with a substantial mortality
rate. In the case of emphysematous pyelitis, if gas is localised to the
collecting system and no obstruction is present, antibiotic therapy alone
appears to be sufficient .
In conclusion, we presented herewith a patient with
emphysematous pyelitis. CT proved to be a good imaging modality for depicting
this disease process as it is sensitive in precisely localising air within the
pelvicalyceal system and eliminating air within the renal parenchyma and/or
perinephric space , thus reliably excluding the more fulminant emphysematous
pyelonephritis as a diagnosis.
Figure 1 Plain abdominal radiograph showing oval radiopacity (*) surrounded by a radiolucent rim (arrow) at the region of the left kidney.
Figure 2 Reformatted sagittal image of contrasted CT scan of the abdomen showing a large obstructing calculus (*) at the left pelvi-ureteric junction, causing gross left hydronephrosis with gas (arrow) noted within the left pelvicalyceal system.
Figure 3 Axial image of contrasted CT scan of the abdomen showing a large obstructing calculus (*) at the left pelvi-ureteric junction, causing gross left hydronephrosis with gas (arrow) noted within the left pelvicalyceal system.
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Wan YL, Lee TY, Bullard MJ et al. Acute gas-producing bacterial renal infection: correlation between imaging findings and clinical outcome. Radiology 1996; 198(2):433-8.
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|Received 27 December 2007; received in revised form 24 March 2008; accepted 9 May 2008
Correspondence: Department of Biomedical Imaging, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia. Tel.: +603-79492069; Fax: +603-79581973; E-mail: email@example.com (Yang Faridah Abdul Aziz).
Please cite as: Kua CH, Abdul Aziz YF,
Air in the kidney: between emphysematous pyelitis and pyelonephritis, Biomed Imaging Interv J 2008; 4(4):e24