Determining which children to evaluate, which tests are most appropriate, and when to obtain studies is critical to develop a rational and consistent approach to this controversial component of UTI.
For a long time, majority opinion favored imaging evaluation of the upper and lower urinary tract in every child following a well-documented first UTI.
(1) All patients with documented UTI should have ultrasound to assess integrity of the urinary tract;
(2) VCUG should be obtained in all patients less than 3 years of age and all patients with or suspected of having pyelonephritis;
(3) No further studies if ultrasound is normal in children older than 3 years or with minimal symptoms at presentation.
There are several reasons for routinely imaging infants and young children with UTI:
(1) a high incidence of VUR is found in this age group, approaching 35 to 50% (70% in children <1 year);
(2) renal scarring following infection is most likely to occur in the first 2 to 4 years of life; and
(3) symptoms are so vague that differentiation between upper and lower tract infection is usually impossible.
Once a decision to image the urinary tract has been reached, the choice of studies must be made.
Cystoscopy, although not an imaging study, directly visualizes the bladder, urethra, and ureteral orifices, but it is extremely invasive, generally requires general anesthesia in children, and offers little advantage over cystography in the evaluation of a child with UTI. Cystoscopy in girls with recurrent cystitis to diagnose any urethral stenosis,or a condition whose existence is seriously questioned, is not indicated.
The intravenous pyelogram (IVP) has largely been replaced by sonography.
Ultrasonography of the kidney and/or the bladder is simple and easy to carry out. Neither radiation exposure nor pain is involved, and it provides very accurate images and information on kidney size, shape, location, and texture . Echogenicity of the kidney may be altered with inflammation, either diffusely (as occurs in pyelonephritis) or focally (as is seen in acute lobar nephronia). Ultrasonography cannot assess renal function, reliably diagnose or exclude VUR, or demonstrate mild scars. Well-established scars can be detected, and renal growth can be documented with repeated studies over time. Assessment of renal growth is an important component of the follow-up of infants and children with VUR .
Color Doppler sonography may permit the evaluation of VUR without invasive catheterization or radiation exposure in the future. Ultrasonography of the bladder is limited by the requirement for a distended bladder. Information is provided on bladder wall thickness, capacity, and residual volume.
Radionuclide imaging of the kidney provides both functional and anatomic information. Renal images demonstrating “cold†spots indicate areas of tubular dysfunction and/or decreased intrarenal blood flow because DMSA is taken up mainly from peritubular blood vessels, and abnormalities may occur in the course of acute parenchymal infection or in areas of scarring, a fact that may result in errors in interpretation of the scan. Because results in animal studies have shown excellent correlation between DMSA scans and anatomic infection, and because no other reliable diagnostic study is available in children, DMSA has been touted as a gold standard for the localization of infection and recommended by some as a routine initial study in children with febrile UTI. Unfortunately, during the acute phase of infection, false positives and false negatives as well as a disturbingly high number of equivocal scans are reported. A sensitivity of 50 to 85% and a specificity of 45 to 90%, along with high cost and concerns regarding prolonged radiation exposure to the renal cortex, dampen enthusiasm for routine use of DMSA scars, but for the detection of renal scars in specific circumstances it may be helpful.
Voiding cystourethrography (VCUG) is performed by catheterizing the bladder and instilling radiocontrast material to distend it. Although the primary goal is to demonstrate or exclude the presence of VUR, the VCUG also provides information on the anatomy, capacity, and function of the bladder. The voiding phase is important to assess completeness of voiding and residual urine and, in boys, to look for urethral valves. If VUR is present, the severity of reflux can be assessed and graded. The disadvantages of a VCUG include its “emotional†invasiveness, the requirement for fluoroscopic x-ray exposure, and the risk of either allergic reaction or iatrogenic UTI. The radionuclide VCUG is similar but involves less gonadal radiation exposure because it avoids fluoroscopy. Although at least as sensitive as contrast cystography in detecting mild degrees of reflux, its assessment of the bladder and urethra is less precise. Because of this limitation but lower radiation exposure, a reasonable approach is to perform the radiocontrast cystogram initially and hold the radionuclide cystogram for subsequent studies if indicated.
Computed tomography (CT) of the kidney provides much the same information as a well-done ultrasound but may be useful in the evaluation of the rare child with suspected renal or perinephric abscess.
The younger the infant with UTI, the more likely an anatomic abnormality of the urinary tract will be found. Therefore, young or febrile children should have an ultrasound carried out promptly because an obstructed, infected kidney is at extremely high risk for damage (pyonephrosis). In an older child, especially if treated as an outpatient, the ultrasound can be done at a more convenient time.
DMSA scanning may be done acutely if determination of parenchymal infection is warranted but if detection of scarring is the objective, this study should be delayed 6 months to 2 years and obtained only if urgently indicated. The best time for the VCUG has long been debated and remains unsettled.
A UTI may interfere with normal ureteral peristalsis and result in transient dilatation and/or VUR. Therefore, to avoid mistaking mild, temporary reflux for chronic VUR, most VCUGs are delayed until the acute infection has been treated and inflammation has been resolved, generally 4 to 8 weeks, although there are no special data to make a firm recommendation. Because of the need for bladder catheterization at the time of the study, the VCUG should be scheduled at an opportune time for a culture, which should routinely be obtained.
(1) All patients with documented UTI should have ultrasound to assess integrity of the urinary tract;
(2) VCUG should be obtained in all patients less than 3 years of age and all patients with or suspected of having pyelonephritis;
(3) No further studies if ultrasound is normal in children older than 3 years or with minimal symptoms at presentation.
There are several reasons for routinely imaging infants and young children with UTI:
(1) a high incidence of VUR is found in this age group, approaching 35 to 50% (70% in children <1 year);
(2) renal scarring following infection is most likely to occur in the first 2 to 4 years of life; and
(3) symptoms are so vague that differentiation between upper and lower tract infection is usually impossible.
Once a decision to image the urinary tract has been reached, the choice of studies must be made.
Cystoscopy, although not an imaging study, directly visualizes the bladder, urethra, and ureteral orifices, but it is extremely invasive, generally requires general anesthesia in children, and offers little advantage over cystography in the evaluation of a child with UTI. Cystoscopy in girls with recurrent cystitis to diagnose any urethral stenosis,or a condition whose existence is seriously questioned, is not indicated.
The intravenous pyelogram (IVP) has largely been replaced by sonography.
Ultrasonography of the kidney and/or the bladder is simple and easy to carry out. Neither radiation exposure nor pain is involved, and it provides very accurate images and information on kidney size, shape, location, and texture . Echogenicity of the kidney may be altered with inflammation, either diffusely (as occurs in pyelonephritis) or focally (as is seen in acute lobar nephronia). Ultrasonography cannot assess renal function, reliably diagnose or exclude VUR, or demonstrate mild scars. Well-established scars can be detected, and renal growth can be documented with repeated studies over time. Assessment of renal growth is an important component of the follow-up of infants and children with VUR .
Color Doppler sonography may permit the evaluation of VUR without invasive catheterization or radiation exposure in the future. Ultrasonography of the bladder is limited by the requirement for a distended bladder. Information is provided on bladder wall thickness, capacity, and residual volume.
Radionuclide imaging of the kidney provides both functional and anatomic information. Renal images demonstrating “cold†spots indicate areas of tubular dysfunction and/or decreased intrarenal blood flow because DMSA is taken up mainly from peritubular blood vessels, and abnormalities may occur in the course of acute parenchymal infection or in areas of scarring, a fact that may result in errors in interpretation of the scan. Because results in animal studies have shown excellent correlation between DMSA scans and anatomic infection, and because no other reliable diagnostic study is available in children, DMSA has been touted as a gold standard for the localization of infection and recommended by some as a routine initial study in children with febrile UTI. Unfortunately, during the acute phase of infection, false positives and false negatives as well as a disturbingly high number of equivocal scans are reported. A sensitivity of 50 to 85% and a specificity of 45 to 90%, along with high cost and concerns regarding prolonged radiation exposure to the renal cortex, dampen enthusiasm for routine use of DMSA scars, but for the detection of renal scars in specific circumstances it may be helpful.
Voiding cystourethrography (VCUG) is performed by catheterizing the bladder and instilling radiocontrast material to distend it. Although the primary goal is to demonstrate or exclude the presence of VUR, the VCUG also provides information on the anatomy, capacity, and function of the bladder. The voiding phase is important to assess completeness of voiding and residual urine and, in boys, to look for urethral valves. If VUR is present, the severity of reflux can be assessed and graded. The disadvantages of a VCUG include its “emotional†invasiveness, the requirement for fluoroscopic x-ray exposure, and the risk of either allergic reaction or iatrogenic UTI. The radionuclide VCUG is similar but involves less gonadal radiation exposure because it avoids fluoroscopy. Although at least as sensitive as contrast cystography in detecting mild degrees of reflux, its assessment of the bladder and urethra is less precise. Because of this limitation but lower radiation exposure, a reasonable approach is to perform the radiocontrast cystogram initially and hold the radionuclide cystogram for subsequent studies if indicated.
Computed tomography (CT) of the kidney provides much the same information as a well-done ultrasound but may be useful in the evaluation of the rare child with suspected renal or perinephric abscess.
The younger the infant with UTI, the more likely an anatomic abnormality of the urinary tract will be found. Therefore, young or febrile children should have an ultrasound carried out promptly because an obstructed, infected kidney is at extremely high risk for damage (pyonephrosis). In an older child, especially if treated as an outpatient, the ultrasound can be done at a more convenient time.
DMSA scanning may be done acutely if determination of parenchymal infection is warranted but if detection of scarring is the objective, this study should be delayed 6 months to 2 years and obtained only if urgently indicated. The best time for the VCUG has long been debated and remains unsettled.
A UTI may interfere with normal ureteral peristalsis and result in transient dilatation and/or VUR. Therefore, to avoid mistaking mild, temporary reflux for chronic VUR, most VCUGs are delayed until the acute infection has been treated and inflammation has been resolved, generally 4 to 8 weeks, although there are no special data to make a firm recommendation. Because of the need for bladder catheterization at the time of the study, the VCUG should be scheduled at an opportune time for a culture, which should routinely be obtained.
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