1. INFECTIONS URINAIRES DU HAUT APPAREIL URINAIRE : ASPECTS EN IMAGERIE TOMODENSITOMETRIQUES SUR UNE REVUE ICONOGRAPHIQUE DE 88 CAS
R.BENMOUSSA, M.SABIRI, N.TOUIL, O.KACIMI, N.CHIKHAOUI
Service de Radiologie des Urgences
CHU Ibn Rochd - Casablanca - Maroc

2. INTRODUCTION
Acute pyelonephritis (APN) is known as an inflammation of the kidney and upper urinary tract, most commonly resulting from bacterial infection of the bladder.
10% to 30% of patients with APN require hospitalisation and may even present with life-threatening complications including shock, septicemia and multi-organ dysfunction syndromes, what shows the importance of assessing diagnosis.
Bacterial nephritis or renal infection can be regarded as a spectrum of clinical entities, progressing from mild APN to renal abscesses or emphysematous pyelonephritis.

3. PURPOSES
To provide through an iconographic review, a support showing different aspects of this disease.
Grading radiological facts as in Picolli’s classification according to severity of lesions.
To demonstrate impact of imaging, especially CT on APN and renal infection radiological analysis.
To recognize on imaging the most common complications of APN and main differentials.

4. PATIENTS AND METHODS Inclusion criterias:
We studied patients showing with suspected diagnosis of APN, during a period of two years (from May 2011 to May 2013).
Inclusion criterias:
Clinical criterias: presence of classical symptoms of APN
Fever
Presence of loin or flank pain with or without lower urinary tract symptoms
Positive urine dipstick for leukocytes and/or nitrites
Biological criterias:
Cytobacteriological urine examination realized but not necesserally positive
All patients underwent first an ultrasound examination then Computed Tomography scanning.

5. CT SCAN TECHNIQUE PARAMETERS PELVIS Scan duration (s) 32 – 40 Pitch
1 – 2
Section thickness (mm) 3
Table speed (mm/s)
3 – 6
Reconstruction interval (mm)
2 – 3
Kilovolt peak
120
Milliampere seconds
280
Use of intravenous contrast +
Reconstruction algorithm
Standard soft tissue

6. RESULTS 88 patients were included in the study.
The diagnosis of APN was established half of cases (44 cases)
Age: 33,2±8,6 years
Gender:
-Women: 78%
-Men: 22%

7. RESULTS Ultrasonography: -diagnosis of APN established: 65,9%
-dismissed diagnosis: 34,1%
The abdominal CT showed in 34,1% of dismissed ultrasonographic diagnosis of APN, 4 cases of perinephitic abscess and many perfusion troubles in the other cases.
Ultrasonographic signs n %
Increase of kidney size with hypoechoic areas 47
53,6
Blurred margins 21
24,4
Reduction of Doppler vascularity 32
36,6

8. RESULTS Microbiological exams: -Escherichia coli: 85,3% -Others: 6,1%
-None: 8,6%

9. DEFINING APN ?
APN can be defined clinically, pathologically or radiologically:
The British Medical Research Concil Bacteriuria Committee defined APN as a clinical syndrome of flank pain, costovertebral tenderness and fever accompanied by laboratory evidences of renal infection including leukocytosis, pyuria, haematuria, bacteriruria, positive urine culture and sometimes bacteraemia.
Hill defined APN pathologically as a suppurative inflammation of the renal parenchyma and pyelocaliceal system typically distributed along one or more medullary rays supporting as ascending route of infection.
Radiologically, APN manifests on contrasted computed tomography (CT) scans as hypoenhancing regions with or without renal swelling, and may be focal or diffused.

10. ROLE OF CT
CT imaging is often the modality of choice for the evaluation of APN and renal abcesses.
It is superior to intravenous urogram or renal ultrasonography in detecting renal parenchymal abnormalities like perinephric stranding, inflammatory masses, decreased or delayed cortical enhancement, kidney enlargement or gas formation, all of which may indicate more severe APN.
Non-contrast CT imaging will be able to rule out an obstructed collecting system requiring urgent decompression and drainage but it is not ideal for diagnosing renal abcesses or APN.

11. NORMAL NEPHROGRAPHIC DEVELOPMENT ON CT
Before CMI
NON ENHANCED
VASCULAR PHASE
10-15 seconds after CMI
CORTICAL NEPHROGRAPHIC PHASE
20-45 seconds after CMI
PARENCHYMAL NEPHROGRAPHIC PHASE
45 seconds to 2 minutes after CMI
EXCRETORY PHASE
2-3 minutes after CMI

12. UNENHANCED CT SCAN THROUGH THE KIDNEYS

13. CT SCAN OBTAINED SECONDS AFTER BEGINNING CONTRAST MATERIEL ADMINISTRATION : CORTICAL NEPHROGRAM WITH A CLEAR CORTICOMEDULLARY INTERFACE

14. CT SCAN OBTAINED AT 45 SECONDS TO 2 MINUTES: GENERALIZED NEPHROGRAM

15. CT SCAN OBTAINED AT 2-3 MINUTES: CONTRAST MATERIAL IN THE COLLECTING SYSTEM

16. ACUTE PYELONEPHRITIS (APN)
Clinical and biological presentation
Clinical signs:
Lumbar pain is unilateral more often than bilateral.
High temperature (fever of 39°C).
Pyuria.
Functional urinary signs (pollakiuria, dysuria).
Positive urine dipstick (screening): positive for leukocytes and nitrites.
Biological Signs:
Cytobacteriological urine examination: bacteriuria ≥ 105/mL, leukocyturia ≥ 104/mL and antibiogram.
Inflammatory signs (polynucleosis, raised CRP and procalcitonin).

17. ACUTE PYELONEPHRITIS (APN)
When do I use CT Scan for diagnosis?
Patients whose clinical diagnosis is unclear.
Patients who fail to respond to conventional médical treatment.
Diabetic patients.
Immunocompromised patients
« The primary value of CT scan is in delineating the extent of the disease process and identifying significant complications such as renal emphysema and abscesses with or without perirenal extension or the presence of urinary obstruction »
Objective

18. ACUTE PYELONEPHRITIS (APN)
CT findings
Typical: « a striated nephrogram on a conventionel CT scan obtained during the excretory phase »
Other signs:
Soft-tissue stranding and thickening of the Gerota’s fascia
Obliteration of the renal sinus
Caliceal effacement due to adjacent affected renal parenchyma
Thickening of the walls of the pelvis and calices
Mild dilatation of the renal pelvis and ureter
CT phase
aspect
Cortical and parenchymal nephrographic phases
Wedge-shaped areas of hypoattenuating cortex and poor corticomedullary differentiation
Excretory phase
Smaller wedge-shaped areas of diminished enhancement and linear band of alternating hyper and hypoattenuation parallel to the axes of tubules and collecting ducts

19. Acute Pyelonephritis in a 42 year-old-woman
Enhanced abdominal CT Scan during the cortical nephrographic phase showing wedge-shaped areas of hypoattenuating cortex in the left kidney which volume is increased

20. Acute pyelonephritis in a 29 year-old-woman
Enhanced helical CT Scan during excretory phase: sriated nephrogram

21. Acute pyelonephritis in a 34 year-old-woman
Enhanced CT Scan in excretory phase: smaller wedge-shaped areas of diminished enhancement and linear band of alternating hyper and hypoattenuation parallel to the axes of tubules and collecting ducts

22. Main differential of APN: RENAL INFARCTION
« Cortical rim sign » is a fine layer of cortical enhancement and is highly suggestive of renal infarction
Right kidney infarction
Contrast-enhanced CT Scan in axial plane: Wedge-shaped enhancement defect of the postérior lip of the right kidney with cortical contrast uptake showing the « cortical rim sign » confirming thet ischaemia is the mechanism of the lesion
Ifergan J, Pommier R, Imaging in upper urinary tract infections. Diagnostic and Interventional Imaging. 2012;93:

23. ACUTE PYELONEPHRITIS (APN)
Keypoints of analysis
Identify the typical lesion
Chatecterize CT finding: Society of Uroradiology
Unilateral or bilateral?
Focal or diffuse?
Focal swelling or no focal swelling?
Renal enlargement or no renal enlargement?
Looking for complications:
Renal emphysema?
Renal abscess?
Perirenal extension?
Presence of renal obstruction?

24. COMPLICATIONS
RENAL ABSCESS
Mechanism: liquefactive necrosis and abscess formation resulting from severe vasospasm and inflammation.
CT Scan findings:
Well-defined mass of low attenuation with a thick, irregular wall or pseudocapsule, which is better imaged with contrast enhancement.
Gas within a low attenuation or cystic mass.
Renal parenchyma around the abscess cavity poorly enhanced on early views, hyperattenuating on delayed views.
Fascial and septal thickening and perinephric fat obliteration.

25. Renal abscess of the left kidney in a diabetic 43 year-old-man
Enhanced helical CT Scan within excretory phase showing a well-defined mass of low attenuation with a thick wall evident with contrast enhancement

26. Renal abscess of the right kidney in a 35 year-old-woman
Enhanced helical CT Scan within parenchymal phase showing a well-defined mass of low attenuation deforming outline of the right kidney

27. Main differential of renal abscess: SURINFECTED RENAL CYST
Thickening and enhancement of the cyst wall and inflammatory changes surronding the affected cyst are highly suggestive of surinfected renal cyst.
Surinfected right kidney cyst
Contrast-enhanced CT Scan in axial plane during the parenchymal nephrographic phase: Thickening and contrast uptake in the wall of a right kidney cyst with oedema of the perilesional parenchyma
Ifergan J, Pommier R, Imaging in upper urinary tract infections. Diagnostic and Interventional Imaging. 2012;93:

28. PICOLLI’S CLASSIFICATION ACCORDING TO SEVERITY
Picolli GB, Colla L, Development of kidney scars after acute uncomplicated pyelonephritis: relationship with clinical, laboratory and imaging data at diagnosis. World J Urol 2006;24:66-73

29. COMPLICATIONS PERINEPHRIC ABSCESS Mechanism:
Rupture of a renal abscess into the perirenal space.
Developing directly from APN
Context: Diabetic patients and patients with septic emboli
CT Scan findings:
Areas of soft-tissue or fluid attenuation within the perirenal space.
May involve the psoas muscle and extend to the pelvis.
Gas occasionally present.
Rarely, a postinflammatory cystic fluid collection < 3cm in diameter without appreciable thickening or enhancement of the wall.

30. Perirenal abscess of the left kidney in a 35 year-old-woman, already having renal abscess 6 days before
Enhanced helical CT Scan within cotical nephographic phase showing a mass of low attenuation deforming outline of the left kidney and extending the perirenal space

31. EMPHYSEMATOUS PYELONEPHRITIS
COMPLICATIONS
EMPHYSEMATOUS PYELONEPHRITIS
Mechanism: fulminant gas-forming infection with commonly E.Coli, Klebsiella pneumoniae and Proteus mirabilis.
Context: symptoms of severe APN in uncontrolled diabetes mellitus patients
CT Scan findings: GAS
Renal or perirenal fluid collections with bubbly or loculated gaz in the parenchyma or collecting system.
Localiszed in the renal parenchyma, the subcapsular, perinephric or pararenal space, the collecting system or occasionally the vascular system.
Differential: CLASSICAL EMPHYSEMATOUS PYELONEPHRITIS which is characterized by parenchymal destruction, streaky or motted gas, and little or no fluid.

32. Emphysematous pyelonephritis in a diabetic 59 year-old-woman presenting with clinical signs of APN
Renal ultrasonography showing the presence of gas in the sinus of the right kidney

33. Emphysematous pyelonephritis in a diabetes mellitus patient
Enhanced CT Scan during parenchymal phase showing the presence of gaz among the right renal parenchyma

34. COMPLICATIONS PYONEPHROSIS
Mechanism: concomitant suppuration of the parenchyma and the collecting system, usually secondary to a calculus and more rarely to other causes of obstruction.
Ultrasonography:
Dilation of the pelvicalyceal system.
Fine mobile or sloping echoes in the calyces.
CT Scan findings:
Thickening of the walls of the renal pelvis.

35. Pyonephrosis in a 52 year-old-man
Contrast-enhanced CT Scan during excretory phase showing a dilated left renal pelvis, with poor excretion and increased density within the renal pelvis.

36. SUMMARY
APN is a severe stat responsible for a considerable mortality if not assessed in time.
The ultrasonography is often insufficient to define APN, but when realized eartly possesses value for looking for obstruction and indicating Ct Scan and ponctions.
Nowadays, abdominal CT Scan is the best exam for assessing upper urinary tract infections and their complications.
Therefore, respecting the recommandations for good CT scan technique is essential for good assessment.

37. REFERENCES
Lim SK, Ng FC, Acute pyelonephritis and renal abscesses in adults: correlating clinical parameters with radiological (computed tomography) severity. Ann Acad Med Singapore 2011; 40:407-13
Picolli GB, Colla L, Development of kidney scars after acute uncomplicated pyelonephritis: relationship with clinical, laboratory and imaging data at diagnosis. World J Urol 2006;24:66-73
Kawashima A, Sandler CM, CT of renal inflammatory disease. Radiographics 1997;17:
Wan YL, Lee TY, Acute gas-producing bacterial renal infection: correlation between imaging findings and clinical outcome. Radiology 1996; 198:
Ifergan J, Pommier R, Imaging in upper urinary tract infections. Diagnostic and Interventional Imaging. 2012;93:
Bruyère F, Carlou G, Boiteux JP, Pyélonéphrites aigues. Prog Urol 2008;18:514-8
Craig WD, Wagner BJ, Travis MD? Pyelonephritis: radiologic-pathologic review. Radiographics 2008;28/255-77
Kawashima A, Leroi AJ. Radiologic evaluation of patients with renal infections. Infect Dis Clin North Am 2003;17:433-56