Editing Pediatrics: Vesicoureteral Reflux (section)

=== Imaging ===

==== Lower Urinary Tract ====
* '''<span style="color:#ff0000">Modality'''
**'''<span style="color:#ff0000">Voiding cystourethrogram (VCUG) and radionuclide cystogram (RNC)''' 
***Two most common forms of direct cystography
***'''<span style="color:#ff0000">Present-day gold standard approaches to detect VUR'''
***'''Both VCUG and RNC require catheterization'''
***'''Radionuclide Cystogram (RNC)'''
**** '''Advantages (2):'''
****# '''Reduced radiation requirements'''
****#* RNC has historically been described as a technique that requires a significantly lower dose of radiation than a regular VCUG, but the advances with modern digital techniques have significantly narrowed the difference between these two imaging modalities.
****# '''Greater sensitivity for grade 2 to 5 VUR'''
**** '''Disadvantage:'''
***** '''Provides much less anatomic detail than does a VCUG'''
*** '''Voiding Cystourethrogram (VCUG)'''
****'''Technique'''
*****Bladder contrast is instilled by gravity after urethral catheterization. Bladder capacity is recorded when contrast influx ceases. Static images record bladder contour, presence of diverticula or ureteroceles, grade of reflux, configuration and blunting of calyces, and intrarenal reflux. Passive or active reflux is demonstrated dynamically during fluoroscopy while filling and voiding, respectively. In addition, bladder neck anatomy, funneling or dilation, and urethral patency are parameters derived from the VCUG.
***** '''Delayed or postvoid films are crucial in documenting clearance of contrast from the upper tracts because retained contrast, particularly with dilated pelvicalyceal systems, could signify the presence of a concomitant UPJ obstruction (UPJO)'''
**Ultrasound
***More recently, to eliminate the need for ionizing radiation, some studies have demonstrated a growing interest in US detection of VUR using either color Doppler imaging
* '''Findings'''
**Parameters that effect direct imaging of VUR (3)''':'''
**# Bladder contraction during voiding
**# Fluid volume instilled into the bladder
**# Presence of infection and therefore inflammation of the UVJ mucosa.
*** '''Even during voiding, reflux may not be demonstrated on a single filling-voiding cycle'''. Several studies have demonstrated a roughly 12-20% '''greater detection rate for VUR if a cyclic study is performed'''
** '''Passive reflux (VUR during filling of the bladder) is generally considered a poor prognostic sign for reflux resolution and suggests the presence of a fixed decompensation of the UVJ.'''
*** Filling assumes far lower intravesical pressure than that of voiding
*** '''Passive reflux is common finding in patients with acquired or neurogenic voiding dysfunction'''
* '''Cystogram during active infection'''
** '''The general consensus has been to delay the voiding study for at least a week or longer to allow for adequate recovery from the acute infection episode.'''
*** Evoking reflux during an active cystitis, by definition, will transmit bacteria to the upper urinary tract and renal pelvis and risks iatrogenic pyelonephritis.
** '''Only if it is imperative to make the diagnosis of reflux in children with a history of recurrent pyelonephritis and repeatedly negative voiding studies in the intercurrent periods should cystography during UTI be considered.'''
*** Some UVJs maintain only borderline antireflux mechanisms, which are competent in a sterile milieu but become incompetent from edema and inflammation associated with mucosal inflammation during cystitis. Such patients may have VCUG studies negative for reflux in the absence of infection but suffer from repeated pyelonephritic episodes. Cystograms in such patients may demonstrate reflux if obtained during clinically active infection, whereas cystogram obtained in the presence of positive urine cultures alone may not.
* '''Diagnostic Controversies: Challenging the Assessment of VUR'''
** '''Uroflowmetry'''
*** A valuable tool in the workup of a patient with vesicoureteral reflux
*** A minimal survey of bladder emptying characteristics can be obtained
**** Lack of smoothness of the flow-velocity curve suggest incomplete relaxation of the bladder outlet during voiding.
***** This implies the existence or development of relatively higher pressures during voiding, which could delay the natural history of VUR resolution or even perpetuate VUR.
**** Increased postvoid residual volume may be a risk factor for UTI.
***** In the setting of passive VUR, carrying infected postvoid residual urine also can lead to ascending infection and pyelonephritis.
** '''Top-Down Approach'''
*** '''Only a dimercaptosuccinic acid (DMSA) renal scan is obtained after a febrile UTI, with cystography reserved only for patients with abnormal scintigraphy findings.'''
**** '''Children with a normal DMSA scan undergo no further evaluation unless they develop recurrent UTI, in which case a VCUG should be obtained'''.
**** Photopenic areas may result from postinfection renal scarring and some renal dysplasia.
**** Vesicoureteral reflux, particularly reflux of higher grades, may result in renal dysplasia, which often appears scintigraphically identical to postinfection pyelonephritic scars.
**** During an episode of active pyelonephritis, the renal scan may show an area of photopenia that later, if it persists, represents renal scarring secondary to the infection.
**** Neither renal scan nor ultrasonography can differentiate accurately between renal dysplasia and renal scarring
*** '''A critical assumption with this approach is that VUR in the absence of scintigraphic renal abnormality is unlikely to cause future renal damage'''
*** '''The top-down approach performs poorly at detecting high-grade VUR''' with a sensitivity and specificity of only 79% and 53%, respectively
* '''American Academy of Pediatrics Guidelines for Febrile UTI Diagnosis and Management in Young Children'''
** '''VCUG should be obtained after second febrile UTI'''
*** Previous recommendation was after the first febrile UTI
*** '''VCUG should be obtained after first febrile UTI if''':
***# US shows hydronephrosis, possible renal scarring or dysmorphism
***# Other findings that suggest high-grade VUR
***# Obstructive uropathy are present
***# Any complex or clinically atypical scenario

==== Upper Urinary Tract ====
* '''Rationale for Serial Assessment of Upper Tracts'''
** '''Pyelonephritis propagated by VUR causes:'''
**# '''Renal scarring'''
**# '''Impedes attainment of full renal growth potential'''
**# '''Increases risk for renovascular hypertension'''
** '''Most parenchymal abnormalities are detected after the first episode of pyelonephritis'''
** A fundamental goal in serial upper tract imaging with VUR is to ascertain whether abnormalities are due to ongoing or resolved reflux and differentiate them from intrinsic developmental disturbances, medical renal disease, or antegrade flow resistance.
** Intensity of upper tract studies should be proportional to the propensity for renal damage
** The challenge in imaging is to differentiate congenital reflux–associated renal dysmorphism from scarring acquired after infection
*** VUR, particularly of higher grades, may result in renal maldevelopment that often appears scintigraphically or sonographically identical to postinfection pyelonephritic scars
* '''Renal US'''
** The mainstay of renal imaging in VUR management
** '''The appearance of the kidneys on ultrasound does not correlate with the absence or presence of reflux, or with its grade'''
** '''Renal resistive index measurements are significantly increased in higher grades of reflux'''
* '''Renal Scintigraphy'''
** '''The gold standard for imaging functioning renal parenchyma is scintigraphy using 99mTc-labeled DMSA.'''
*** The radiotracer is taken up only by functioning proximal tubular tissue mass, where it binds for several hours.
**** Because pyelonephritis impairs tubular uptake of radiotracer, these areas will fail to radioemit photons and appear as unexposed or underexposed regions in the resultant renal cortical images
**** DMSA scanning provides 98% sensitivity and 92% specificity for scar detection
*** The uptake of DMSA provides a good proportional representation of glomerular filtration
*** No consensus exists on the precise use of DMSA scanning in reflux management.
* DMSA and ultrasonography are often used complementarily, particularly when knowledge of relative renal function is desired since all DMSA defects are not necessarily scars.