Editing CUA: Antenatal hydronephrosis (2017) (section)

=== Imaging ===

==== Renal-bladder US (RBUS) ====

===== <span style="color:#ff0000">Indications (1) =====
#'''<span style="color:#ff0000">APD ≥7 mm in third trimester'''
#*'''<span style="color:#ff0000">Verbatim (summary section): All significant AHN should be investigated with a postnatal RBUS. Most centres define significant AHN in the third trimester as APD ≥7 mm'''
#** ''Verbatim (RBUS section): All children with AHN should have a complete abdominopelvic US, with particular attention to both the kidneys and bladder. [likely meant “significant” ANH rather than "all" patients]''

===== Timing =====
* '''Avoid US in the first 2 days of life due to concern of understaging secondary to neonatal oliguria.'''
* The acceptable delay in the timing of the first postnatal US is controversial, with the SFU suggesting anywhere from 1‒4 weeks (see Figure 1 from Original Guideline for details, discussed below). '''In cases where immediate postnatal management is required such as PUV, US should not be delayed.'''

===== Technique =====

*Fasting for a RBUS is unnecessary.
*RBUS should include assessment of 
**Cranio-caudal length of the kidneys
**Degree of echogenicity and corticomedullary differentiation
**SFU grade of hydronephrosis
**Maximal APD on transverse axial view of the renal pelvis
**Diameter of both proximal and distal ureter if dilated
**Degree of bladder filling
**Detrusor thickness or presence of bladder trabeculation
**Diverticula
**Ureterocele
**Posterior urethral dilation in males.
* '''A full bladder should prompt a period of observation with re-imaging post-void to assess for the capability to empty the bladder and to assess whether the hydronephrosis improves post-void'''

==== Voiding cysto-urethrography (VCUG) [or nuclear cystography] ====
* '''Goal is to distinguish an obstructive cause of AHN from VUR''', not due to concern over UTI
** ≈'''16% of infants with ANH are found to have VUR, with 25% of such cases occurring in the non-dilated, contralateral renal unit.'''
* '''Nuclear cystography is more sensitive than VCUG for VUR with less radiation exposure'''

===== Indications =====
* '''<span style="color:#ff0000">The AUA guidelines on VUR similarly recommends that VCUG in the neonate with:'''
*# '''<span style="color:#ff0000">High-grade (SFU grade ≥3) hydronephrosis'''
*# '''<span style="color:#ff0000">Hydroureter'''
*# '''<span style="color:#ff0000">An abnormal bladder on ultrasound</span>''' (late-term prenatal or postnatal)
*# '''<span style="color:#ff0000">Develops a UTI on observation'''
* '''VCUG is not necessary in the evaluation of isolated LGHN (SFU 1‒2) with normal renal parenchyma and symmetric renal size'''
* '''<span style="color:#ff0000">Any infant with suspected bladder outlet obstruction (e.g., PUV) should have an urgent VCUG.''' 
**'''<span style="color:#ff0000">Findings associated with bladder outlet obstruction (7):'''
**# '''<span style="color:#ff0000">Dilated posterior urethra'''
**# '''<span style="color:#ff0000">Distended bladder'''
**# '''<span style="color:#ff0000">Thick or trabeculated bladder'''
**# '''<span style="color:#ff0000">History of oligohydramnios'''
**# '''<span style="color:#ff0000">Severe bilateral hydronephrosis'''
**# '''<span style="color:#ff0000">Increased renal cortical echogenicity''' (hyper-echogenicity)
**# '''<span style="color:#ff0000">Renal cortical cysts'''

===== Technique =====

*'''Steps by step'''
*# '''A scout view''' for assessment of spine anomalies, presence of significant constipation or urinary stones
*# '''Catheter is inserted'''
*#* '''A balloon catheter should not be used''', as the balloon can obscure the filling defect characteristic of a ureterocele.
*#* The amount of urine removed should be recorded and the urine sent for analysis and culture as indicated.
*#* The bladder should be gravity filled until the first void occurs, with recording of the bladder capacity.
*# '''Voiding views''' of the urethra with post-void views of the bladder.
*# '''Delayed imaging''' after the post-void image may be required if there is VUR into a dilated renal pelvis or ureter so as to assess for concomitant UPJO and UVJO
** '''A cyclical study with at least two fill and void cycles will increase the detection of VUR.'''
**#

==== Diuretic renography ====
* '''<span style="color:#ff0000">Nuclear tracer'''
**'''<span style="color:#ff0000">MAG3 diuretic renogram is test of choice for the assessment of the function of a hydronephrotic kidney'''
***Permits assessment of both the differential renal function (DRF) and the drainage time
*** Dimercaptosuccinic acid (DMSA) study can be considered to establish early split function in cases of neonates or premature infants, since the DRF in this study is not influenced by an immature GFR.
* '''<span style="color:#ff0000">Indications (1)'''
*# '''<span style="color:#ff0000">APD >15 mm or high-grade hydronephrosis (SFU 3-4) with VCUG was negative for VUR''' 
*#*'''To identify other potential causes of hydronephrosis (such as UPJO, UVJO)'''
**'''Not necessary in the evaluation of isolated LGHN (SFU 1‒2) with normal renal parenchyma and symmetric renal size'''
*Renogram should include a report of 
**Differential renal function, which can vary from 45‒55%
**Cortical transit time, which is normal up to 5 minutes
**Half-time
**Shape of the curve
* '''Test results can be influenced by'''
** '''Poor renal function (single kidney glomerular filtration rate [GFR] <15 ml/min)'''
** '''Poor hydration'''
** '''Massively dilated collecting system'''
** '''Full bladder'''
** '''Dilated distal ureter'''
* Renograms can be performed at any age, as long as they are used as a baseline study for serial comparison'''.'''