Evaluation of the urinary tract Ultrasonography (US)
8.2 Symptomatic upper urinary tract infection in adults
Introduction
As in children, most symptomatic upper urinary tract infections in adults are ascending from the lower urinary tract, due to contamination from the fecal flora, mostly byE. coli. Other bacteria, such asEnterobacter, Klebsiella, Proteus, Pseudomonasand enterococci may also occur, but are more common in patients with recurrent or complicated UTI or as a result of antibiotic treatment.
UTI in adults is over-represented in certain patient groups
• sexually active and pregnant women, diabetics, elderly and those with indwelling bladder catheters.
• patients with urinary obstruction from e.g. prostate hyperplasia, ureteral stones, malignant pelvic tumors, spinal injuries or iatrogenic ureteral injuries, e.g. after gynecological or rectal surgery.
• Vesicoureteral reflux (VUR) may play a role in transportation of bacteria from the bladder to the upper tract, but is rarely documented as a causal factor in adults with pyelonephritis.
Secondary VUR may appear in adults due to neoplastic or inflammatory processes in the bladder wall, or from bladder surgery.
Patients with obstructive abnormalities are at increased risk of serious complications, such as septicemia (uro-sepsis) or abscess formation. Hence, imaging in UTI in adults focuses more on the detection of complications, and less on the identification of risk factors for future renal damage, since clinically significant scarring is only rarely seen to develop in adults. Imaging of the urinary tract in adults is usually considered only after repeated UTI episodes or if a complication is suspected. Also, VUR is not routinely searched for in adults. Finally, ionizing radiation is less of an issue in adults, at least in the middle-aged or elderly. All these factors are reflected in the choice of imaging protocols in adult UTI.
With the recent advancements in CT technology, multidetector CT is rapidly taking over as the imaging modality of choice in adult UTI.
Clinical features
Symptoms may differ from those in children, and underlying or complicating factors are relatively frequent.
Symptoms
• Fever>38◦C
• Flank pain, tenderness on palpation over kidney area
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• Malaise, nausea and vomiting may occur
• Frequency and dysuria
• Focal urinary tract symptoms may be absent, especially in elderly
• Hypotension, tachypnea and deteriorating clinical status may signal septicemia.
Laboratory tests and findings
• Urinary dip stick sensitive for nitrite and granulocyte-esterase is positive
• Significant bacteriuria, pyuria and sometimes hematuria
• Urinary culture positive (definition of bacterial type and antibacterial resistance pattern is mandatory)
• Blood culture should be obtained if septicemia is suspected
• Elevated C-reactive protein (CRP), sometimes elevated serum creatinine.
Long-term effects
• Renal scarring, usually developing in early childhood, may result in
◦ hypertension
◦ complications during pregnancy
◦ reduced renal function (if scarring is bilateral and severe).
Pathology
• Patho-anatomic changes in the kidney parenchyma, collecting system and perirenal tissues are similar to those described for children.
• Distribution of infection in the renal parenchyma is usually patchy with spared areas, but may be more generalized.
• Focal vasospasm, tubular obstruction and interstitial oedema are factors underlying the CT-finding of low attenuation in affected parts of the parenchyma.
• UTI with certain ureas-producing bacteria, such asProteus mirabilis, may induce stone formation.
• Renal scarring due to UTI occurs mainly in young children, and is rarely documented in adults, although it may occasionally be shown after pyelonephritis associated with obstruction or abscess formation.
Imaging findings
Females with acute, febrile UTI who respond promptly to antibacterial treatment need no radiological imaging. However, if an adult female has 2–3 UTI episodes in one year, imaging is motivated. UTI is less common in men, and recommendations vary. Some claim that imaging should always follow upper UTI in men, while others suggest imaging only after recurrent infection. In patients with diabetes or immunosuppression, early imaging should be considered.
Indications for imaging in adults with febrile UTI/pyelonephritis are:
• acute, febrile UTI with suspicion of concomitant urinary tract obstruction, e.g. ureteral stone (needs acute imaging).
• acute, febrile UTI that does not respond to antibacterial treatment (needs acute imaging).
• repeated febrile UTI/pyelonephritis episodes in men and women.
Imaging may confirm inflammation of the kidney, but the main purpose is to:
• detect underlying urinary tract obstruction, that may require acute treatment by, e.g.
percutaneous pyelostomy (nephrostomy).
• detect renal or perirenal abscess formation, that may require drainage.
The most effective imaging method in adult UTI is multidetector CT, which has replaced urography in many institutions. Ultrasonography may show dilatation of the upper urinary tract, but is not sufficient by itself for detection or assessment of the full extent of renal and perirenal inflammation, obstruction or ureteral stones.
Computed tomography (CT) The CT examination
• should include a non-enhanced scan including the entire urinary tract (kidneys, ureters, bladder)
• should include an early contrast-enhanced scan, obtained in the nephrographic phase (60– 100 s after start of contrast medium injection)
• should include a late scan in the excretory phase (6–8 min after start of contrast injection), to allow visualization of the collecting system and ureters
• the two contrast-enhanced scans can be combined by first injecting half the volume of contrast medium, wait for 8 min and then inject the other half of contrast medium volume, followed by scanning 60–100 s after the start of the second contrast medium injection.
Non-contrast-enhanced CT may demonstrate
• inflammatory swelling of the affected kidney.
• slight reduction in parenchymal attenuation in areas of focal edema.
• inflammatory reaction in the perirenal fat (perinephric stranding) (Fig. 8.14a, b), (similar changes occur with obstruction, trauma, vascular disorders).
• spread of inflammatory reaction to Gerota’s fascia (thickening) and pararenal space.
• dilatation of the renal pelvis (hydronephrosis) and ureter (hydroureter) (Fig. 8.14b, c).
• underlying urinary stones, including those that are ‘non-opaque’ at plain radiography (kidneys-ureters-bladder, KUB) (Fig. 8.14c).
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(a)
(c)
(b)
Figure 8.14 Non-enhanced CT of the urinary tract in an adult patient with fever and right-sided flank pain. (a) Swelling of the right kidney is noted, as compared to the left one, and there is fullness of the renal pelvis. Increased linear and patchy densities, so called stranding (arrows) are seen in the fatty tissue surrounding the kidney, indicating inflammation and/or urinary stasis.
(b) CT section at a more caudal level demonstrates marked perirenal stranding and widening of the proximal part of the right ureter (long arrow). Note normal ureteral diameter (short arrow) and absence of perirenal stranding on the left side. (c) CT section at a more caudal level demonstrates a stone (arrow) in the ureter, causing hydroureter and hydronephrosis. Ureteral obstruction combined with fever indicates pyonephrosis, a medical emergency that requires antibiotics and percutaneous drainage.
• gas in the renal parenchyma, collecting system or perirenal tissues (see ‘Emphysematous pyelonephritis’ below).
Contrast-enhanced CT may demonstrate
• decreased parenchymal attenuation
◦ Typically, sharply or diffusely demarcated, unifocal or multifocal wedge-shaped or rounded low-attenuating areas, extending from the papilla to the renal cortex, corre- sponding to poorly functioning parenchyma, are seen.
◦ Occasionally, the entire kidney is diffusely involved, resulting in renal enlargement, poor enhancement and reduced contrast excretion.
◦ Other infiltrative processes with decreased parenchymal attenuation should be kept in mind, such as renal infarct or neoplasia (e.g. renal or transitional cell carcinoma, myeloma, leukemia).
• reduced corticomedullary differentiation.
Figure 8.15 Delayed imaging after contrast-enhanced CT of the kidneys in a patient with acute, right-sided pyelonephritis. Retained contrast material is noted in the right kidney due to impaired tubular function, causing a striated pattern (striation). Note that contrast material has cleared from the left kidney and the collecting system at this time-point.
• delayed nephrogram (contrast enhancement) in affected parts of the kidney.
• striated nephrogram, i.e. alternating thin bands of high and low attenuation in the affected parenchyma, that
◦ is due to obstructed tubules alternating with intervening normal tubules
◦ may persist over time (persistent nephrogram), while non-affected parenchyma has been cleared of contrast material (Fig. 8.15)
◦ may also be due to e.g. obstruction, renal vein thrombosis or renal contusion.
• inflammatory thickening of the renal pelvis wall (urothelium).
• abscess formations and spread to the surrounding tissues (Fig. 8.7).
• occurrence and degree of urinary obstruction, provided that late imaging in the excretory phase is performed.
Ultrasonography
• is widely available, easy for the patient and involves no harmful radiation
• is operator-dependent (skill and experience) and patient-dependent (more difficult in obese or large patients)
• may show hypo- or hyperechogenic areas, renal enlargement and loss of corticomedullary differentiation, but does often not show full extent of renal and perirenal inflammation
• Doppler and i.v. contrast material may improve detection of pyelonephritis
• may show inflammatory thickening of the renal pelvis wall (urothelium)
• demonstrates dilatation of the renal pelvis (hydronephrosis) with high accuracy, but can not confirm or rule out obstruction
• may demonstrate pyonephrosis, i.e. pus in a widened renal pelvis/ureter, by showing thick echogenic content and layering of debris/urine
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• does not show underlying ureteral stones sufficiently well
• should not be used as single imaging modality in adult UTI
• can be used in pregnant women or otherwise when ionizing radiation is an issue, if necessary combined with single plain radiographs to improve detection of stones
• in pregnant women, dilatation of the collecting system and ureters may be caused by physiological hormonal changes, mechanical obstruction from the enlarged uterus, UTI, or a combination of these factors.
Urography
• is largely being replaced by multidetector computed tomography (CT)
• may show inflammatory swelling of the affected kidney, but this is an unreliable sign since there is considerable normal variation in size of the two kidneys
• may show impaired parenchymal contrast enhancement of the affected kidney, but in most cases (75%) urography appears normal in UTI
• demonstrates most, but far from all, urinary stones on pre-contrast (plain) radiographs (KUB)
• demonstrates occurrence, grade and location of urinary tract obstruction and hydronephro- sis/hydroureter on images obtained after i.v. contrast medium injection. This may require delayed imaging after 30 min. up to several hours
• may be useful in demonstrating papillary necrosis and medullary sponge kidney (tubular ectasia).
MRI
• is less widely available than CT but involves no harmful radiation
• Intravenous contrast media (gadolinium) should be used with caution in patients with reduced renal function (risk of nephrogenic systemic fibrosis)
• is able to show renal and perirenal inflammation, abscesses, hydronephrosis and obstruc- tion with high accuracy
• may be useful in assessing the extent of renal and perirenal inflammation (e.g.
gadolinium-enhanced 3D FLASH sequences), as well as in assessing the collecting system (e.g. MR urography with HASTE-sequences)
• is less accurate than CT in identifying urinary stones
• is usually not routinely employed for acute or non-acute imaging in adult UTI
• may be useful for problem solving in individual cases
• may be useful for imaging children, young adults or pregnant women, when ionising radiation is an issue.
Radionuclide studies
• Renography may be employed for estimation of renal function and assessment of obstruc- tion (see above, UTI in children)
• DMSA scintigraphy may demonstrate acute renal inflammatory involvement in UTI, but does not give information on underlying causes or complications, and is therefore usually not routinely employed in adults
• As in children, DMSA scintigraphy is very sensitive in revealing post-pyelonephritic scarring, but it is not routinely employed in adults.
Voiding cystourethrography (VCUG)
• is not routinely performed in adults with UTI
• VUR may persist into adulthood or occur secondary to bladder pathology, and may occasionally contribute to UTI and, rarely, flank pain.
Summary
• Adults with uncomplicated febrile UTI/acute pyelonephritis who respond promptly to antibacterial treatment need no radiological imaging.
• Imaging in UTI/acute pyelonephritis should be considered in patients with diabetes and those with growth of uncommon infecting bacteria.
• Adults withrepeatedepisodes of febrile UTI/pyelonephritis should have imaging of the urinary tract performed, in order to reveal any underlying cause.
• Patients with febrile UTI/acute pyelonephritis, who do not respond to antibacterial treat- ment, and patients suspected of having complications (obstruction, uncommon bacteria), should haveacuteimaging of the urinary tract.
• Febrile UTI/pyelonephritis in combination with urinary obstruction is an emergency, that should initiateimmediateimaging and treatment (antibiotics and percutaneous drainage), in order to reduce the risk of potentially life-threatening septicemia.
• Multidetector-CT without and with i.v. contrast medium is the preferred method to demon- strate the extent of inflammation and any underlying cause of the UTI, such as ureteral stone and/or obstruction, and to reveal complications, such as abscess formation.