Computerized tomography and acute pyelonephritis in children. A clinical correlation

Acute focal bacterial nephritis, pyonephrosis and renal abscess in children

BACKGROUND-AIM

Acute focal bacterial nephritis (AFBN), renal abscess and pyonephrosis are uncommon and not fully addressed forms of urinary tract infection (UTI) which may be underdiagnosed without the appropriate imaging studies. Here, we review the characteristics and outcome of these renal entities in children managed at a single medial centre.

PATIENTS AND METHODS

The medical files of all children hospitalized for episodes of AFBN, renal abscess and pyonephrosis during a 10-year period (2003-2012) were reviewed.

RESULTS

Among the 602 children hospitalized for UTI, 21 presented with AFBN, one with abscess and three with pyonephrosis. All 25 children (13 girls), ranging in age from 0.06 to 13.4 years, were admitted with fever and an impaired clinical condition, and 18 had urological abnormalities. More than one lesion, often of different types, were identified in 11 episodes. Urine cultures from 13 episodes grew non-Escherichia coli pathogens and those from two episodes were negative. Antibiotics were administered for 14-60 days, and emergency surgery was required in three cases. During follow-up, 13 patients underwent corrective surgery. Permanent renal lesions were identified in 16 patients.

CONCLUSIONS

AFBN, renal abscess and pyonephrosis should be suspected in children with severe presentation and urological history. Appropriate imaging is crucial for management planning. Prognosis is often guarded despite appropriate treatment. Based on the results of this study we propose a management algorithm.

Effective duration of antimicrobial therapy for the treatment of acute lobar nephronia

OBJECTIVE

Effective treatment of acute lobar nephronia (ALN) can prevent its progression to renal abscess. The goal of this prospective study was to compare the treatment efficacy for pediatric patients who had ALN with a 3- vs 2-week intravenous plus oral antimicrobial-therapy regimen.

METHODS

Patients who were suspected of having an upper urinary tract infection underwent a systematic scheme of ultrasonographic and computed tomographic (CT) evaluation for ALN diagnosis. Patients with positive CT findings were enrolled and randomly allocated with serial entry for either a total 2-week or a 3-week antibiotic treatment regimen. Antibiotics were changed from an intravenous form to an oral form 2 to 3 days after defervescence of fever. Follow-up clinical evaluations and urine-culture analyses were performed 3 to 7 days after cessation of antibiotic treatment. Patients with persistent infection or relapse were considered as treatment failures.

RESULTS

A total of 80 patients with ALN were enrolled. Forty-one patients were treated with a 2-week antimicrobial protocol, and the other 39 patients were treated with a 3-week course. Seven treatment failures, 1 persistent infection, and 6 infection relapses were identified, all of which were in the 2-week treatment group. Prolonged fever before admission and positive Escherichia coli growth (>10(5) colony-forming units per mL) in urine culture were noted as risk factors for treatment failure. All treatment failures were managed successfully with an additional 10-day antibiotic course.

CONCLUSION

A total of 3 weeks of intravenous and oral antibiotic therapy tailored to the pathogen noted in cultures should be the treatment of choice for pediatric patients with ALN.

Magnetic resonance imaging of experimental pyelonephritis in rabbits

RATIONALE AND OBJECTIVES

An experimental model of acute focal pyelonephritis was developed in the New Zealand White rabbit, with initial imaging evaluation performed using high-field contrast-enhanced magnetic resonance (MR) in six animals.

METHODS

The left kidney was visualized fluoroscopically after intravenous injection of iodinated contrast. A 0.1 mL mixture of agarose/Streptococcus faecalis was then injected percutaneously into the kidney at the corticomedullary junction with a 25-gauge needle. The animals were imaged at 1.5 tesla on day 5 after injection of bacteria. Breathhold T2-weighted and T1-weighted scans were acquired prior to contrast injection. Using an MR-compatible power injector, 0.3 mmol/kg gadoteridol was then administered, with both dynamic and delayed postcontrast scans obtained. The lesion was confirmed in each animal by gross and microscopic exam.

RESULTS

The area of acute focal pyelonephritis was somewhat difficult to identify on precontrast scans. The lesion was mildly hyperintense on T2-weighted scans and slightly hypointense to isointense on T1-weighted scans relative to normal surrounding renal parenchyma. On early dynamic turbo-fast low-angle shot scans, the lesion could be identified due to differential tissue enhancement. Direct visualization of the lesion, with increased conspicuity relative to precontrast scans, was possible because of delayed positive enhancement at 60 seconds postcontrast. Lesion conspicuity, assessed by signal difference/noise ratio, increased from 0 +/- 5 precontrast to a peak of 12 +/- 6 at 60 seconds postcontrast (P = 0.003; n = 6).

CONCLUSIONS

On dynamic contrast-enhanced MR, acute focal pyelonephritis can demonstrate transient positive contrast enhancement (using a contrast dose of 0.3 mmol/kg) relative to surrounding normal renal parenchyma. This appearance is due to hyperconcentration of the contrast agent in normal parenchyma and T2 effects. The pattern is opposite that seen in spiral computed tomography.

Focal bacterial nephritis (lobar nephronia) in children

We report 13 patients with 16 episodes of acute lobar nephronia diagnosed in a prospective study that was conducted among 210 hospitalized children with urinary tract infection. In 30 episodes of urinary tract infection, a hypoechogenic or hyperechogenic lesion was found. Twenty patients underwent computed tomography, and in 16 of them acute lobar nephronia was diagnosed. Evolution to renal abscess occurred in 25%. Prolonged intravenous antibiotic treatment was sufficient in all cases.

Correlative imaging of the kidney

The proliferation of imaging methods for the kidney and urinary tract, combined with advances in technology and the introduction of new techniques, has created uncertainty in selecting the most efficient method for evaluating many problems encountered in clinical medicine. The main advantage of nuclear medicine lies in demonstrating the pathophysiology involved. Recent developments in Doppler ultrasound and magnetic resonance imaging with different pulse sequences and paramagnetic contrast agents also have shown promise for imaging physiological processes. However, there is little literature to support their advantage over nuclear medicine procedures in many common clinical situations. The complementary nature of nuclear medicine studies in the imaging evaluation of hydronephrosis, renal artery stenosis, flank pain, renal mass, pyelonephritis, and the transplant kidney is reviewed.

Rational use of CT in acute pyelonephritis: findings and relationships with reflux

Enhanced renal CT scanners were performed in 38 children (82% girls) to rule out acute pyelonephritis. Patients were divided in 2 groups on the basis of clinical presentation and bacteriology data. In patients of group A (n = 16, preliminary study), upper urinary tract infection (UTI) was certain. CT confirmed the diagnosis in all but 3 patients (a 2-year-old child and 2 patients with UTI developed on prior obstruction). In subsequently studied patients of group B (n = 22), clinical findings or bacteriology data were negative or questionable. CT made the diagnosis of acute pyelonephritis in 11 patients. As well as DMSA scintigraphy, CT scanner can help to diagnose or to rule out upper UTIs in difficult cases. In all boys of both groups, ipsilateral vesico-ureteric reflux (VUR) was found by subsequent voiding cystourethrography (VCUG) on the side of pyelonephritis. In girls, this correlation was shown in only 7 of the 25 kidneys with pyelonephritis. This result supports the hypothesis of a gender-dependent contamination. We believe that absence of radiologic reflux cannot exclude the possibility of bacterial crossings of ureteric meatus capable to lead to genuine upper UTIs.

Computerized tomography in acute pyelonephritis: the clinical correlations

Computerized tomography was performed on 19 patients diagnosed as having uncomplicated acute pyelonephritis. The relationship was investigated among the laboratory findings, presence of flank pain, clinical course and severity of the lesions detected by computerized tomography. In patients febrile for less than 2 weeks healing as assessed by computerized tomography took an average of 76 days. However, in patients with repeated febrile episodes occurring for longer than 2 weeks healing was delayed until an average 232 days after onset. Computerized tomography findings generally correlated well with the erythrocyte sedimentation rate, C-reactive protein level, and presence of pyuria and flank pain. However, in patients with a prolonged course computerized tomography proved to be a more reliable indicator of progress than either the results of laboratory tests or the symptoms. In conclusion, computerized tomography was useful in the diagnosis, assessment of severity and evaluation of healing of acute pyelonephritis.

The role of scintigraphy in urinary tract infection

There is controversy regarding the role of radiological imaging for urinary tract infection (UTI). The "gold standard" has been the intravenous pyelogram (IVP). Yet, the IVP has a very limited value with only about 25% of children with pyelonephritis demonstrating abnormalities. Ultrasound (US) has recently been advocated as a replacement for the poorly sensitive and poorly specific IVP. However, comparative studies between US and IVP indicate only an equivalent sensitivity and specificity. Cortical scintigraphy with Technetium-99m glucoheptonate (99mTc GH) or 99mTc dimercaptosuccinic acid (99mTc DMSA) has also been advocated as a means of differentiating parenchymal (pyelonephritis) from nonparenchymal (lower UTI) involvement in UTI. The clinical presentation may be misleading especially in the infant and child in whom an elevated temperature, flank pain, shaking chills, or an elevated sedimentation rate are often lacking. The clinician attempts to localize the site of infection for it has a direct bearing upon the therapy. A collecting system infection can often be eradicated with a single oral dose of an appropriate antibiotic, whereas renal parenchymal involvement requires IV therapy for an extended interval. Cortical scintigraphy can localize the site of infection with a high degree of accuracy. Recent studies report a sensitivity of 86% and specificity of 81% of pyelonephritis. This is in contrast to the IVP with a sensitivity of only 24% and US with a sensitivity of only 42%. The scintigraphic appearance of parenchymal infection of the kidney is a spectrum of minimal to gross defects reflecting the degree of histologic involvement that spans from a mild infection to frank abscess. Cortical scintigraphy can be used to monitor the evolution of scarring following infection. Cortical scintigraphy with 99mTc DMSA or 99mTc GH is the method of choice for the initial evaluation of UTI. Not only does it have a very high sensitivity and specificity for differentiating parenchymal from collecting system disease, but it also provides an accurate quantitative measurement of function and in combination with radioiodinated orthoiodohippurate renography and Lasix (furosemide; Abbott Laboratories, North Chicago) diuresis will also differentiate significant obstruction from stasis. The use of radionuclide techniques opens new vistas for the investigation of UTI. Cortical scintigraphy should become the gold standard by which other technologies, therapy, and theoretical considerations of pyelonephritis are measured.